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Vision Ranges Linked to Quran and Hadith

Hussain Omari

Physics Dept./ Mutah University/ Jordan

rashed@mutah.edu.jo

الملخص:

قال رسول اللّه صلى اللّه عليه وسلّم: (إذا سمعتم صياح الديكة فاسألوا الله من فضله ، فإنها رأت ملكا ، وإذا سمعتم نهيق الحمار فتعوذوا بالله من الشيطان ، فإنه رأى شيطانا) . يبين المقال أنّ نطاق الرؤية (Vision Range) يختلف من كائن إلى آخر كما يرشد إليه هذا الحديث الشريف : الديكة ترى بعض الملك ، والحمار يرى بعض الشياطين ، وفي الحالتين لا يرى الإنسان شيئاً من هذا. وإِنَّ الشَّيْطَان يَرَانا هُوَ وَقَبِيلُهُ مِنْ حَيْثُ لا نراهم : (إِنَّهُ يَرَاكُمْ هُوَ وَقَبِيلُهُ مِنْ حَيْثُ لَا تَرَوْنَهُمْ) . وثبت أنَّ أسيدَ بنَ حضيرٍ ، بينما هو ، ليلةً ، يقرأُ في مربدِه إذ إذ جالت فرسُه ثلاث مرّات . ... قال فانصرفتُ . وكان يحيى قريبًا منها . خشيتُ أن تطأَه . فرأيتُ مثلَ الظُلَّةِ . فيها أمثالُ السُّرُجِ . عرجتْ في الجوِّ حتى ما أراها . فقال رسولُ اللهِ صلَّى اللهُ عليهِ وسلَّمَ " تلك الملائكةُ كانت تستمعُ لك . ولو قرأتَ لأصبحتْ يراها الناسُ . ما تستتِرُ منهم ؛ ممّا يشير إلى أنّها أصلاً مستترة عنّا ولا يمكننا رؤيتها.

(Narrated Abu Huraira: The Prophet said, "When you hear the crowing of cocks, ask for Allah's Blessings for (their crowing indicates that) they have seen an angel. And when you hear the braying of a donkey, seek Refuge with Allah from Satan for (its braying indicates) that it has seen a Satan." ). This hadith refers to the scientific fact that Vision Ranges differ for different creatures: Cocks can see some of the angels, and a donkey can see some demons, and in both cases the human does not see anything from this. The devil and its tribe see us, while we do not see them (He (Satan) and his tribe watch you from a position where ye cannot see them).

Meanwhile a companion of the Prophet reading Al-Kahf surah and beside him a horse hitched with two ropes, a rotating cloud starts approaching him and make his horse alienate. When the day light appears, he went to the Prophet peace be upon him and mentioned that to him. Prophet said those tranquility descend for the Qur-an. According to another version, these angels were listening to you. Had you read more, it will become apparent to people, and no more hidden.

المبحث الأوّل : اختلاف نطاق الرؤية من كائن إلى آخر كما بيّنت الآيات والأحاديث

الفرع الأوّل: الديكة ترى بعض الملك، والحمار يرى بعض الشياطين وفي الحالتين لا يرى الإنسان شيئاً من هذا

جاء في الحديث الصحيح ، الذي يرويه أبو هريرة، قال رسول اللّه صلى اللّه عليه وسلّم: (إذا سمعتم صياح الديكة فاسألوا الله من فضله ، فإنها رأت ملكا ، وإذا سمعتم نهيق الحمار فتعوذوا بالله من الشيطان ، فإنه رأى شيطانا) (الراوي: أبو هريرة المحدثون:

البخاري - المصدر: صحيح البخاري - الصفحة أو الرقم: 3303، مسلم - المصدر: صحيح مسلم - الصفحة أو الرقم: 2729، أبو داود - المصدر: سنن أبي داود - الصفحة أو الرقم: 5102، الألباني - المصدر: صحيح الترمذي - الصفحة أو الرقم: 3459، الألباني - المصدر: صحيح أبي داود - الصفحة أو الرقم: 5102).

يؤكّد هذا الحديث الشريف أنّ الديكة ترى بعض الملك ، كما وأنّ والحمار يرى بعض الشياطين ، وفي الحالتين لا يرى الإنسان شيئاً من هذا.

الفرع الثاني: إِنَّهُ يَرَاكُمْ هُوَ وَقَبِيلُهُ مِنْ حَيْثُ لَا تَرَوْنَهُمْ

وجاء في الآية الكريمة: (يَا بَنِي آدَمَ لَا يَفْتِنَنَّكُمُ الشَّيْطَانُ كَمَا أَخْرَجَ أَبَوَيْكُمْ مِنَ الْجَنَّةِ يَنْزِعُ عَنْهُمَا لِبَاسَهُمَا لِيُرِيَهُمَا سَوْآتِهِمَا إِنَّهُ يَرَاكُمْ هُوَ وَقَبِيلُهُ مِنْ حَيْثُ لَا تَرَوْنَهُمْ) (الأعراف 27).

[27] O ye Children of Adam! let not Satan seduce you, in the same manner as he got your parents out of the Garden, stripping them of their raiment, to expose their shame: for he and his tribe watch you from a position where ye cannot see them: We made the Evil Ones friends (only) to those without Faith.

" قَالَ بَعْض الْعُلَمَاء : فِي هَذَا دَلِيل عَلَى أَنَّ الْجِنّ لَا يُرَوْنَ ; لِقَوْلِهِ " مِنْ حَيْثُ لَا تَرَوْنَهُمْ " قِيلَ : جَائِز أَنْ يُرَوْا ; لِأَنَّ اللَّه تَعَالَى إِذَا أَرَادَ أَنْ يُرِيَهُمْ كَشَفَ أَجْسَامهمْ حَتَّى تُرَى . قَالَ النَّحَّاس : " مِنْ حَيْثُ لَا تَرَوْنَهُمْ " يَدُلّ عَلَى أَنَّ الْجِنّ لَا يُرَوْنَ إِلَّا فِي وَقْت نَبِيّ ; لِيَكُونَ ذَلِكَ دَلَالَة عَلَى نُبُوَّته ; لِأَنَّ اللَّه جَلَّ وَعَزَّ خَلَقَهُمْ خَلْقًا لَا يُرَوْنَ فِيهِ , وَإِنَّمَا يُرَوْنَ إِذَا نُقِلُوا عَنْ صُوَرِهِمْ . وَذَلِكَ مِنْ الْمُعْجِزَات الَّتِي لَا تَكُون إِلَّا فِي وَقْت الْأَنْبِيَاء صَلَوَات اللَّه وَسَلَامه عَلَيْهِمْ . قَالَ الْقُشَيْرِيّ : أَجْرَى اللَّه الْعَادَة بِأَنَّ بَنِي آدَم لَا يَرَوْنَ الشَّيَاطِين الْيَوْم . وَفِي الْخَبَر ( إِنَّ الشَّيْطَان يَجْرِي مِنْ اِبْن آدَم مَجْرَى الدَّم ) . وَقَالَ تَعَالَى : " الَّذِي يُوَسْوِس فِي صُدُور النَّاس " [ النَّاس : 5 ] ." (القرطبي). وَقَدْ جَاءَ فِي رُؤْيَتِهِمْ أَخْبَارٌ صَحِيحَةٌ (إِذَا نُقِلُوا عَنْ صُوَرِهِمْ)، ومنها ما رواه أبو هريرة: (وكَّلني رسولُ اللهِ بحفظ زكاةِ رمضانَ ، فأتانى آتٍ ، فجعل يحثو من الطعامِ ، فأخذتُه ، فقلتُ : لأَرفعنَّك إلى رسولِ اللهِ ، قال : إني محتاجٌ ، وعليَّ دَينٌ وعِيالٌ ، ولي حاجةٌ شديدةٌ فخلَّيتُ عنه ، فأصبحتُ، فقال النَّبيُّ: يا أبا هريرةَ ما فعل أسيرُك البارحةَ؟ قال : قلتُ : يا رسولَ اللهِ شكا حاجةً شديدةً وعِيالًا ، فرحمتُه فخلَّيتُ سبيلَه ، قال : أما إنه قد كذبَك وسيعود فعرفت أنه سيعودُ ، لقولِ رسولِ اللهِ : أنه سيعود ، فرصدتُه ، فجاء يحثو من الطعامِ ( وذكر الحديثَ إلى أن قال : ) فأخذتُه ( يعني في الثالثةِ ) فقلتُ : لأَرفعنَّكَ إلى رسولِ اللهِ ، و هذا آخرُ ثلاثِ مراتٍ تزعم أنك لا تعود ، ثم تعود ، قال : دَعْني أُعلِّمْك كلماتٍ ينفعك اللهُ بها قلتُ : ما هنَّ ؟ قال ، إذا أَوَيتَ إلى فراشِك ، فاقرأ آيةَ الكرسيِّ : ( اللهُ لَا إِلَهَ إِلَّا هُوَ الْحَيُّ الْقَيُّومُ ) حتى تختم الآيةَ ، فإنك لن يزال عليك من الله حافظٌ ، ولا يقربُك شيطانٌ حتى تصبحَ فخلَّيتُ سبيلَه ، فأصبحتُ ، فقال لي رسولُ اللهِ : ما فعل أسيرُك البارحةَ ؟ قلتُ : يا رسولَ اللهِ زعم أنه يُعلِّمُني كلماتٍ ينفعني اللهُ بها ، فخلَّيتُ سبيلَه ، قال: ما هي؟ قلتُ : قال لي : إذا أوَيتَ إلى فراشِك فاقرأْ آيةَ الكُرسيِّ ، من أولها حتى تختم الآيةَ ( اللهُ لَا إِلَهَ إِلَّا هُوَ الْحَيُّ الْقَيُّومُ ) ، و قال لي : لن يزال عليك من الله حافظٌ ، و لا يقربُك شيطانٌ حتى تصبحَ و كانوا أحرصَ شيءٍ على الخير فقال النبيُّ : أما إنه قد صدَقَك ، و هو كذوبٌ ، تعلم مَن تخاطبُ منذ ثلاثِ ليالٍ يا أبا هريرةَ ؟ قلتُ : لا قال : ذاك الشيطانُ) (الراوي: أبو هريرة المحدث:الألباني - المصدر: صحيح الترغيب - الصفحة أو الرقم: 610، خلاصة حكم المحدث: صحيح).

الفرع الثالث: ولو قرأتَ لأصبحتْ يراها الناسُ ما تستتِرُ منهم

- (أنَّ أسيدَ بنَ حضيرٍ ، بينما هو ، ليلةً ، يقرأُ في مربدِه . إذ جالتْ فرسُه . فقرأ . ثم جالتْ أخرى . فقرأ . ثم جالتْ أيضًا . قال أسيدٌ : فخشيتُ أن تطأَ يحيى . فقمتُ إليها . فإذا مثلُ الظُلَّةِ فوقَ رأسي . فيها أمثالُ السُّرُجِ . عرجت في الجوِّ حتى ما أراها . قال فغدوتُ على رسولِ اللهِ صلَّى اللهُ عليهِ وسلَّمَ فقلتُ : يا رسولَ اللهِ ! بينما أنا البارحةُ من جوفِ الليلِ أقرأُ في مِربدي . إذ جالت فرسي . فقال رسولُ اللهِ صلَّى اللهُ عليهِ وسلَّمَ " اقرأ . ابنَ حضيرٍ ! " قال : فقرأتُ . ثم جالت أيضًا . فقال رسولُ اللهِ صلَّى اللهُ عليهِ وسلَّمَ " اقرأ . ابنَ حضيرٍ ! " قال : فقرأتُ . ثم جالت أيضًا . فقال رسولُ اللهِ صلَّى اللهُ عليهِ وسلَّمَ " اقرأ . ابنَ حضيرٍ ! " قال فانصرفتُ . وكان يحيى قريبًا منها . خشيتُ أن تطأَه . فرأيتُ مثلَ الظُلَّةِ . فيها أمثالُ السُّرُجِ . عرجتْ في الجوِّ حتى ما أراها . فقال رسولُ اللهِ صلَّى اللهُ عليهِ وسلَّمَ " تلك الملائكةُ كانت تستمعُ لك . ولو قرأتَ لأصبحتْ يراها الناسُ . ما تستتِرُ منهم " .) ( الراوي: أبو سعيد الخدري المحدث:مسلم - المصدر: صحيح مسلم - الصفحة أو الرقم: 796، خلاصة حكم المحدث: صحيح).

يتضح من هذا الحديث الشريف أنّ رؤية أسيدَ بنَ حضيرٍ للملائكة كانت كرامة له لما قرأه من القرآن في جوف تلك اللّيلة. فإنّ رؤيته هذه للملائكة كانت استثناءً خصّه اللهُ به بدليل : (ولو قرأتَ لأصبحتْ يراها الناسُ . ما تستتِرُ منهم ). فالأصل أنّ الملائكة تستتِرُ من الناس ولا نستطيع رؤيتها على هيئتها .

- (وحدثنا يحيى بن يحيى أخبرنا أبو خيثمة عن أبي إسحق عن البراء قال (كان رجل يقرأ سورة الكهف وعنده فرس مربوط بشطنين فتغشته سحابة فجعلت تدور وتدنو وجعل فرسه ينفر منها فلما أصبح أتى النبي صلى الله عليه وسلم فذكر ذلك له فقال تلك السكينة تنزلت للقرآن) (البخاري: باب نزول السكينة لقراءة القرآن ، ص 548 ، رقم 795).

- (Meanwhile a companion of the Prophet reading Al-Kahf surah and beside him a horse hitched with two ropes, a rotating cloud starts approaching him and make his horse alienate. When the day light appears, he went to the Prophet - peace be upon him - and mentioned that to him. Prophet said those tranquility descend for the Qur-an. According to another version, these angels were listening to you. Had you read more, it will become apparent to people, and no more hidden).

الفرع الرابع: هنالك ما لا يبصرهُ الإنسان

(فَلَا أُقْسِمُ بِمَا تُبْصِرُونَ * وَمَا لَا تُبْصِرُونَ * إِنَّهُ لَقَوْلُ رَسُولٍ كَرِيمٍ) (الحاقة س 69 : 38-40)

(So I do call to witness what ye see * And what ye see not * That this is verily the word of an honoured Messenger) (S. 69, V. 38-40)

أورد ابن كثير في تفسيره : (يَقُول تَعَالَى مُقْسِمًا لِخَلْقِهِ بِمَا يُشَاهِدُونَهُ مِنْ آيَاته فِي مَخْلُوقَاته الدَّالَّة عَلَى كَمَالِهِ فِي أَسْمَائِهِ وَصِفَاته. وَمَا غَابَ عَنْهُمْ مِمَّا لَا يُشَاهِدُونَهُ مِنْ الْمُغَيَّبَات عَنْهُمْ إِنَّ الْقُرْآن كَلَامه وَوَحْيه وَتَنْزِيله عَلَى عَبْده وَرَسُوله الَّذِي اِصْطَفَاهُ لِتَبْلِيغِ الرِّسَالَة وَأَدَاء الْأَمَانَة فَقَالَ تَعَالَى " فَلَا أُقْسِم بِمَا تُبْصِرُونَ وَمَا لَا تُبْصِرُونَ" . (إِنَّهُ لَقَوْلُ رَسُولٍ كَرِيمٍ( يَعْنِي مُحَمَّدًا صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ أَضَافَهُ إِلَيْهِ عَلَى مَعْنَى التَّبْلِيغ لِأَنَّ الرَّسُول مِنْ شَأْنه أَنْ يُبَلِّغ عَنْ الْمُرْسَل وَلِهَذَا أَضَافَهُ فِي سُورَة التَّكْوِير إِلَى الرَّسُول الْمَلَكِيّ " إِنَّهُ لَقَوْل رَسُول كَرِيم ذِي قُوَّة عِنْد ذِي الْعَرْش مَكِين مُطَاع ثَمَّ أَمِين" وَهَذَا جِبْرِيل عَلَيْهِ السَّلَام ثُمَّ قَالَ تَعَالَى " وَمَا صَاحِبكُمْ بِمَجْنُونٍ " يَعْنِي مُحَمَّدًا صَلَّى اللَّه عَلَيْهِ وَسَلَّمَ " وَلَقَدْ رَآهُ بِالْأُفُقِ الْمُبِين " (التكوير آية 23) يَعْنِي أَنَّ مُحَمَّدًا رَأَى جِبْرِيل عَلَى صُورَته الَّتِي خَلَقَهُ اللَّه عَلَيْهَا " وَمَا هُوَ عَلَى الْغَيْب بِضَنِينٍ " أَيْ بِمُتَّهَمٍ " وَمَا هُوَ بِقَوْلِ شَيْطَان رَجِيم " .

وفي الحديث الشريف :

(يا عائشةُ هذا جبريلُ يقرأُ عليك السلامَ . قالت : قلتُ : وعليه السلامُ ورحمةُ اللهِ ، ترى ما لا نرى ، تريدُ رسولَ اللهِ صلى اللهُ عليهِ وسلَّمَ .) (الراوي : عائشة أم المؤمنين ، المحدث : البخاري ، المصدر : صحيح البخاري ، الصفحة أو الرقم: 6249 ، خلاصة حكم المحدث : [أورده في صحيحه] وقال : تابعه شعيب. وقال يونس والنعمان عن الزهري: (وبركاته) ، انظر شرح الحديث رقم 4731 (

(أن النبيَّ صلى الله عليه وسلم قال لها: يا عائشةُ ، هذا جبريلُ يقرأُ عليكِ السلامَ. فقالت: وعليه السلامُ ورحمةُ اللهِ وبركاتُه، ترى ما لا أرى، تريدُ النبيَّ صلى الله عليه وسلم.) (الراوي : عائشة أم المؤمنين ، المحدث : البخاري ، المصدر : صحيح البخاري ، الصفحة أو الرقم: 3217، خلاصة حكم المحدث : [صحيح[ ، شرح الحديث :

قال النَّبيُّ صلَّى الله عليه وسلَّم: يا عائشةُ، هذا جبريلُ يَقرَأُ عليكِ السَّلامَ، أي: يُهديكِ السَّلامَ، ويُحيِّيكِ بتحيَّةِ الإسلامِ، فقالتْ: وعليه السَّلامُ ورحمةُ الله وبركاتُه، أي: ردَّتِ التَّحيَّةَ بأحسَنَ منها، ثمَّ قالتْ: تَرى ما لا أَرى؛ تُريدُ النَّبيَّ صلَّى الله عليه وسلَّم، أي: إنَّك يا رسولَ الله، ترى جبريلَ الذي لا أَراه.

وفي الحديثِ: فضيلةٌ ظاهرةٌ لأمِّ المؤمنين عائشةَ رضي الله عنها.

وفيه: بَعْثُ السَّلام وتبليغُه، وبَعْثُ الأجنبيِّ السَّلامَ إلى الأجنبيَّةِ الصَّالحةِ إذا لم يُخُفْ ترتُّبُ مَفْسَدةٍ.

(يا عائشُ ! هذا جبريلُ يقرأُ عليك السلامَ . قالت فقلت : وعليه السلامُ ورحمةُ اللهِ . قالت : وهو يرى ما لا أرى .) (الراوي : عائشة أم المؤمنين ، المحدث : مسلم ، المصدر : صحيح مسلم ، الصفحة أو الرقم: 2447 ، خلاصة حكم المحدث : صحيح ، انظر شرح الحديث رقم 4731 (

(إنَّ جبريلَ يقرأُ عليك السَّلامَ ، قالت : وعليه السَّلامُ ورحمةُ اللهِ وبركاتِه ، ترَى ما لا نرَى) (الراوي : عائشة أم المؤمنين ، المحدث : الألباني ، المصدر : صحيح النسائي ، الصفحة أو الرقم: 3963 ، خلاصة حكم المحدث : صحيح ، انظر شرح الحديث رقم 4731 (

Many species can see frequencies outside the visible spectrum:

العديد من أنواع الحيوانات يمكنه أن يرى ويبصر تردّدات خارج الطيف المرئي:

النحل وكذلك العديد من الحشرات ترى الضوء فوق البنفسجي. وفي بحث النحلة عن الرحيق ؛ فإنّها ترى الزهور في الطيف فوق البنفسجي أجمل من رؤية الإنسان للزهور في الطيف المرئي. وكذلك الطيور فإنّها ترى في الطيف فوق البنفسجي (300–400 nm) ، ومع تزايد الطول الموجي ؛ فإنّ قدرة الطيور على الإبصار تتوقّف عند الطول الموجي (590nm) ؛ أي قبل بداية اللّون البرتقالي مباشرة. وترى الطيور نفسها أكثر جمالاً ممّا تبدو للإنسان ، وذلك لوجود علامات على ريشها لا تظهر إلا في الطيف فوق البنفسجي.

Many species can see light with frequencies outside the "visible spectrum," which is defined in terms of human vision. Bees and many other insects can detect ultraviolet light, which helps them find nectar in flowers. Plant species that depend on insect pollination may owe reproductive success to their appearance in ultraviolet light, rather than how colorful they appear to humans. Birds, too, can see into the ultraviolet (300–400 nm), and some have sex-dependent markings on their plumage (ريشها) that are visible only in the ultraviolet range.^[2][3] Many animals that can see into the ultraviolet range, however, cannot see red light or any other reddish wavelengths. Bees' visible spectrum ends at about 590nm, just before the orange wavelengths start. Birds, however, can see some red wavelengths, but not as many as humans. The common goldfish is the only animal that can see both infrared and ultraviolet light. (http://en.wikipedia.org/wiki/Visible_spectrum).

المبحث الثاني : الرؤية الليلية

Night vision (From Wikipedia, the free encyclopedia :

http://en.wikipedia.org/wiki/Night_vision)

Night vision is the ability to see in low light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range. Humans have poor night vision compared to many animals, in part because the human eye lacks a tapetum lucidum.^[1]

تتطلّب الرؤية الليلية كفاية في كلّ من : سعة المدى الطيفي ، وكذلك كفاية في شدّة الطيف.

Types of ranges (أنواع من النطاقات)

Spectral range (المدى الطيفي) :

Night-useful spectral range techniques can sense radiation that is invisible to a human observer. Human vision is confined to a small portion of the electromagnetic spectrum called visible light. Enhanced spectral range allows the viewer to take advantage of non-visible sources of electromagnetic radiation (such as near-infrared or ultraviolet radiation). Some animals can see using much more of the infrared and/or ultraviolet spectrum than humans.

بعض الحيوانات يمكنها الرؤية على نطاق واسع من الأطوال الموجيّة (من الأشعة تحت الحمراء إلى الأشعة فوق البنفسجيّة) . وبالتالي فإنّها تستقبل وتوظّف كمية كافية من شدّة الطيف ؛ فترى في الظلام الحالك.

Intensity range (مدى شدّة الإشعاع)

Sufficient intensity range is simply the ability to see with very small quantities of light.^[2]

Many animals have better night vision than humans do, the result of one or more differences in the morphology and anatomy of their eyes. These include having a larger eyeball, a larger lens, a larger optical aperture (the pupils may expand to the physical limit of the eyelids), more rods than cones (or rods exclusively) in the retina, and a tapetum lucidum.

Enhanced intensity range is achieved via technological means through the use of an image intensifier, gain multiplication CCD, or other very low-noise and high-sensitivity array of photodetectors.

Biological night vision (الرؤية الليلية الحيوية)

In biological night vision, molecules of rhodopsin in the rods of the eye undergo a change in shape as they absorb light. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light. Exposed to a spectrum of light, the pigment immediately bleaches, and it takes about 30 minutes to regenerate fully, but most of the adaptation occurs within the first five or ten minutes in the dark. Rhodopsin in the human rods is less sensitive to the longer red wavelengths of light, so traditionally many people use red light to help preserve night vision as it only slowly depletes the eye's rhodopsin stores in the rods and instead is viewed by the cones. However the US submarine force ceased using red lighting for night adaptation after studies found little significant advantage of using low level red over low level white lighting.^{[3] [4]} Many animals have a tissue layer called the tapetum lucidum in the back of the eye that reflects light back through the retina, increasing the amount of light available for it to capture. This is found in many nocturnal animals (activity during the night and sleeping during the day) and some deep sea animals, and is the cause of eyeshine. Humans lack a tapetum lucidum.

كثير من الحيوانات الليلية لديها بساط من طبقة أنسجة (tapetum lucidum) تقع في الجزء الخلفي من العين (بينما لا توجد هذه الطبقة لدى الإنسان). يقوم هذا البساط بعكس الضوء إلى شبكية العين، مما يزيد من كمية الضوء المتاحة للالتقاط. كما وتوجد طبقة الأنسجة هذه في أعين بعض الحيوانات التي تعيش في أعماق البحار. تسهم هذه الطبقة في زيادة شدة الضوء المتاح في النظام البصري ، ممّا يسمح بالرؤية الليلية رغم الإضاءة المنخفضة . وهذا يفسّر السبب في لمعان عيون هذه الحيوانات في اللّيل.

Nocturnal mammals have rods with unique properties that make enhanced night vision possible. The nuclear pattern of their rods changes shortly after birth to become inverted. In contrast to contemporary rods, inverted rods have heterochromatin in the center of their nuclei and euchromatin and other transcription factors along the border. In addition, the outer nuclear layer (ONL) in nocturnal mammals is thick due to the millions of rods present to process the lower light intensities of a few photons. Rather than being scattered, the light is passed to each nucleus individually.^[5] In fact, an animal's ability to see in low light levels may be similar to what humans see when using first- or perhaps second-generation image intensifiers.

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Infrared detection in animals (رؤية الأشعة تحت الحمراء لدى الحيوانات)

(http://www.mapoflife.org/topics/topic_311_Infrared-detection-in-animals/)

Categories: Arthropods: Insects, Mammals, Reptiles, Senses

التصنيفات: المفصليات، الحشرات ، والثدييات ، والزواحف، و حواسها

Some snakes are famous for 'seeing' infrared, but did you know that their heat-sensing abilities are rivalled by (ينافسها) some beetles (الخنافس) that can detect forest fires over considerable distances?

Vision is defined by its access to the visible electromagnetic spectrum. Many animals, notably insects and birds, can see into the ultraviolet, although this comes with the joined dangers that these short wavelengths (10-400 nm) are high energy and potentially biologically destructive. At the opposite end of the visible spectrum are orange and red, and there has been considerable speculation whether any optical system could register infrared, drawing upon a suitably adapted opsin. The reason to be sceptical (يكون متشككا) is that the radiation of these long wavelengths (750 nm-1 mm) is of low energy, and indeed to date there is no direct evidence for infrared vision. We can, of course, sense it as radiant heat, but several times animals have independently evolved systems of infrared detection that in a number of respects are closely analogous to the eye. In a variety of organisms, transducers (محولات الطاقة) process incoming infrared radiation into a sensory signal that is interpreted by the brain and in at least one case (the snakes) is integrated with visual information. Obviously, infrared detection is ultimately involved with heat sources, but these can vary from 'warm-blooded' prey (snakes, vampire bats (الخفافيش مصّاصة الدماء) and bed bugs) to forest fires (three independent examples in the beetles (الخنافس)).

Infrared detection in vertebrates (رؤية الأشعة تحت الحمراء لدى الفقاريات)

Snakes (الأفاعي)

Infrared detection is probably best known from the snakes, where thermosensitive pits on the head have evolved at least twice - once in the pit vipers (Crotalinae) and probably once in the more ancient boas and pythons (which in some taxonomies are united in the family Boidae). The infrared-sensing pit organs of boids and crotalines are similar with regard to their ultra structure and electrophysiological function, but differ in number, location and overall morphology. While the three or more labial pits of boids are relatively simple, the single loreal pair of crotalines that is located between eye and nostril has a more complex structure. It follows the design of a bolometer, with a thin membrane suspended above a lower air-filled chamber. In both pit types, the heat-sensitive membrane is highly vascular and innervated with sensory dendrites, which are formed from terminal masses of the trigeminal nerve. A recent study has suggested that these nerve fibres are richly endowed with presumed infrared sensors, heat-sensitive ion channels of the TRPA1 type (orthologues of which mediate chemosensation in mammals and other vertebrates). Thus, infrared detection is probably indirect, involving a thermo transduction mechanism, rather than a direct photochemical reaction analogous to the activation of opsins in the vertebrate eye. Still snakes basically 'see' infrared, as the thermal signals are combined with visual information in the optic tectum. The localisation of 'warm-blooded' prey was long assumed to be the sole function of infrared detection in snakes, but heat pits seem to be more general-purpose organs that might also be used for behavioural thermoregulation and perhaps predator detection or den site selection.

Vampire bats (الخفافيش مصّاصة الدماء)

There is some evidence for an independently evolved capacity to detect infrared radiation in vampire bats . These mammals cut up the skin of other vertebrates with their razor-sharp teeth to lick up the blood. They evidently locate their 'warm-blooded' prey with the help of three heat-sensitive pits on their nose that are thermally insulated from the surrounding tissue. A specific nucleus in the brain seems to have important similarities in terms of histology and location to the equivalent infrared nucleus found in snakes.

Infrared detection in insects (رؤية الأشعة تحت الحمراء لدى الحشرات)

In terms of convergence, the insects provide a far more striking example than the vertebrates, because the capacity to detect infrared has evolved several times in this group. Analogous to snakes and vampire bats, the blood-sucking bed bugs (e.g. in the genera Cimex and Leptocimex) employ this sensory modality to help locate their 'prey', evidently using a cave-like organ situated on the antennae.Amongst the hymenopterans, a parasitoid braconid wasp possesses a peculiar type of antennal sensillum that is inferred to be a wave-guide for infrared perception and might play a role in finding a potential host.

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Night Vision in Animals (الرؤية الليلية لدى الحيوانات)

(http://dmohankumar.wordpress.com/2010/04/12/night-vision-in-animals/)

The Night time world is never closed for nocturnal animals. Unlike humans, many animals possess adaptations that allow them to see even when the night sky is very dark. Animals have developed amazing adaptations to their environments. Most nocturnal animals have large eyes relative to their body size. This adaptation, along with the ability to dilate their pupils far wider than humans can, maximizes the amount of light entering into the eye.

Night Vision

Night vision is the ability to see in a dark environment. Night vision is mainly due to two adaptive features: Sufficient spectral range and Sufficient intensity range.

Spectral range

Human vision is confined to a small portion of the electromagnetic spectrum called visible spectrum. It extends between 450 and 750 nanometers wavelengths. Below 450 nm is the Ultraviolet spectrum and above 750 nm is the Infrared spectrum. Some animals can see using the infrared or ultraviolet spectrum.

Intensity range

Sufficient intensity range is the ability to sense very small quantities of light. Although humans can detect single photons under ideal conditions, the neurological noise filters limit sensitivity to a few tens of photons. The night vision of animals is due to one or more differences in the morphology and anatomy of their eyes. These adaptations include large eyeball, large lens, large optical aperture, more rods in the retina, presence of a tapetum lucidum, etc.

Large eyes in Nocturnal Animals

Nocturnal animals have large eyes, wider pupil, large lens and increased retinal surface to collect more light. Some animal species have evolved tubular eyes as part of their evolution to collect more light. Many nocturnal animals cannot move their eyes but they have extraordinary rotational ability of the neck. For example. Owls can rotate their neck through 270°. This helps to increase the night vision.

Some animals have a spherical lens and widened cornea to compensate for reduced eye movement. This along with a large cornea increases the animal’s field of vision. So they can see better in night even without moving the head.

Physiology of Night vision

The vertebrate eyes have Photosensitive cells called Rods and Cones. Rods are elongated cells mainly confined in the periphery of the retina. These are meant for Dim vision in low light and for peripheral vision (الرؤية المحيطية). Rods, are extremely light sensitive and their sensitivity is about 500 times greater than the sensitivity of cones. Only one photon is required to stimulate a rod to send a signal to the brain. Nocturnal mammals have rods with unique properties that make enhanced night vision possible. The nuclear pattern of their rods changes shortly after birth to become inverted. Inverted rods have heterochromatin in the center of their nuclei and euchromatin and other transcription factors along the border. The outer nuclear layer in nocturnal mammals is thick due to the presence of millions of rods present to process the lower light intensities of a few photons. Light is passed to each nucleus individually.

Cones on the other had are pointed cells confined in the central part of the retina. These are meant for Central vision, Bright vision and Colour vision. Rods have photosensitive pigment called Rhodopsin and cones have Iodopsin.

Role of Rhodopsin

The molecules of Rhodopsin in the rods undergo a change in shape as light is absorbed by them. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light. When exposed to light, it immediately bleaches, and it takes about 30 minutes to regeneratefully. Most of the adaptation occurs within the first five or ten minutes in the dark. Rhodopsin is less sensitive to the longer red wavelengths of light. So many people use red light to preserve night vision.

Role of Tapetum

Many animals have a tissue layer called the Tapetum lucidum in the back of the eye that reflects light back through the retina. This increases the amount of light entering into the retina. This is found in many nocturnal animals and some deep sea animals. This causes the phenomenon of eye shine in these animals. Tapetum lucidum is absent in human eye. The shining of eyes in Dogs and Cats in vehicle head light is due to this reflective retina.

Vision in Different groups of Animals

Different types of visual sense exist in animals to adapt them with the environment. Here are some examples of how some animals see the outside world.

Dog and Cats - They have night vision and can see moving objects rather than the stationary ones. Their eyes are much more sensitive to movement. Dogs and cats are color blind and see only very pale shades of color but they have better peripheral and night vision. Tapetum lucidum is also present in them to reflect light into the retina.

Hawk - Hawk’s vision is equivalent to 20/5. Normal vision for people is 20/20. Therefore Hawk can see an object from 20 feet that most people can see from 5 feet.

Snakes – They use their normal eyes during the daytime to see things. During the day time , a snake’s vision dependents on the movement of prey. They ignore any prey that is completely motionless. At night snakes will use Pit Organs to sense infrared rays. Pit organs can pick up infrared heat signals from warm objects in their surroundings.

Falcon – Distant vision is high in Falcon. They can see a 10 cm. object from a distance of 1.5 km.

Bees – Bees can see light between wavelengths 300 nm & 650 nm and they can see polarized light.

Ants - Ants can see polarized light.

Octopus – Octopus is the largest Mollusc and its retina contains 20 million photoreceptors. Their eye has a flicker fusion frequency of 70/sec in bright light. The pupil of the eye is rectangular in shape.

Fish - Some fish can see the infrared wavelengths. They have only rods in the retina. About 25 million rods/sq. mm of the retina. This high density of photoreceptors helps them to detect the dim Bio luminescence in the ocean depths.

Fly - The eye of flies has a flicker fusion rate of 300/sec. Flicker fusion rate is the frequency with which the “flicker” of an image cannot be distinguished as an individual events of the electromagnetic spectrum.

Shark – Shark has no retinal cones, and therefore cannot detect colors. Shark’s eyes are designed to pick up as much light as possible, in order to see in water . But their vision is not as acute.

Bats - Bats can detect warmth of an animal from about 16 cm away using its “nose-leaf”.

Penguin – Penguin is well adapted to see under water. They have flat cornea that allows for clear vision underwater. Penguins can also see into the ultraviolet range.

Not all animals see the world as humans do. For many animals, the world is seen in fuzzy shades of gray, or very “washed out” and pale colors. But some animals can see in total darkness, or even see colors beyond the visual spectrum, that humans have never seen. Still others can use binocular vision to spot prey from thousands of feet away.

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Publisher Summary

Birds can see ultraviolet (UV) light because, unlike humans, their lenses and other ocular media transmit UV, and they possess a class of photoreceptor, which is maximally sensitive to violet or UV light, depending on the species. Birds have a tetra chromatic color space, as compared to the trichromacy of humans. Birds, along with some reptiles and fish, also possess double cones in large numbers and a cone class. This chapter discusses a range of behavioral experiments, from several species, which show that UV information is utilized in behavioral decisions, notably in foraging and signaling. Removal of UV wavelengths affects mate choice even in species that are colorful to humans. These studies emphasize that avian and human color perceptions are different and that the use of human color standards, and even artificial lighting, may produce misleading results. However, genuinely objective measures of color are available, as are, importantly, models for mapping the measured spectra into an avian color space

(http://www.sciencedirect.com/science/article/pii/S0065345408601059).

Ultraviolet vision in birds: What is its function? ([1])

Abstract

Although UV vision was first demonstrated in birds in the early 1970s, its function is still unknown. Here we review the evidence for UV vision in birds, discuss the special properties of UV light, lay out in detail hypotheses for the function of UV vision in birds and discuss their plausibility. The main hypotheses are that UV vision functions: (i) in orientation, (ii) in foraging and (iii) in signaling. The first receives support from studies of homing pigeons, but it would be unwise to conclude that orientation is UV's primary function in all birds. It is especially important to test the signaling hypothesis because bird plumage often reflects UV and tests of theories of sexual selection have virtually always assumed that birds perceive plumage “colours” as humans do. A priori this assumption is unlikely to be correct, for unlike humans, birds see in the UV, have at least four types of cones and have a system of oil droplets which filters light entering individual cones

(http://www.sciencedirect.com/science/article/pii/004269899490149X).

Ultraviolet vision and band-colour preferences in female zebra finches, Taeniopygia guttata

· SARAH HUNT, INNES C. CUTHILL, JOHN P. SWADDLE, and ANDREW T.D. BENNETT

Abstract

Zebra finches have previously been found to have preferences for particular colours of both natural and artificial traits among opposite sex con specifics. For example, in some studies female zebra finches preferred males wearing red leg bands to orange-banded and unbanded birds and rejected light green-banded males. In other studies, females also preferred males with red beaks to orange-beaked males. However, several authors have failed to replicate these results. We show that females may fail to show a colour preference because of the absence or removal of ultraviolet light under experimental conditions. In mate-choice trials, females observing males through filters that transmitted ultraviolet preferred red-banded males but where females viewed males through ultraviolet-blocking filters, no such preference was observed. Further investigation revealed that the lack of a colour preference when ultraviolet was absent was probably due to the change in overall appearance of the bird, rather than the change in appearance of the rings themselves. This work highlights the importance of proper consideration of the sensory capabilities of animals in experimental design, particularly with regard to the role of ultraviolet light in avian colour perception (http://www.sciencedirect.com/science/article/pii/S0003347297905406).

Animal Behaviour

Volume 58, Issue 4, October 1999, Pages 809–815

Preferences for ultraviolet partners in the blue tit

· SARAH HUNT, INNES C. CUTHILL, ANDREW T.D. BENNETT, and RICHARD GRIFFITHS

Abstract

The preference of female blue tits, Parus caeruleus, is correlated with the brightness of the ultraviolet (UV) crest (قمة); there is also assortative mating (زواج نسقي) with respect to the crest's UV/violet chroma. However, manipulation of plumage reflectance is necessary to infer a direct causal link between UV plumage (ريش الطيور) and mate choice. We gave both male and female blue tits a choice between a UV-reflecting (‘UV+’) partner and a partner whose UV plumage reflectance had been removed (‘UV−’). Male blue tits significantly preferred UV+ females. Similarly, female blue tits tended to prefer UV-reflecting males, but their UV+ preferences were nonsignificant. Neither sex showed a preference when conspecifics were replaced by a heterospecific. This study suggests mutual mate choice but male choice may be more strongly influenced by the visual appearance of potential mates. This is one of a few studies to show male mate preferences and the first demonstration of a direct relationship between UV reflectance and male mate choice (http://www.sciencedirect.com/science/article/pii/S0003347299912149).

Ultraviolet vision and foraging in terrestrial vertebrates

رؤية الأشعة فوق البنفسجية والبحث عن الطعام في الفقاريات الأرضية

Johanna Honkavaara, Minna Koivula, Erkki Korpimäki, Heli Siitari, and Jussi Viitala

Tetrachromatic colour vision, based on four ‘main’ colours and their combinations, is probably the original colour vision in terrestrial vertebrates. In addition to human visible waveband of light (400–700 nm) and three main colours, it also includes the near ultraviolet part of light spectrum (320–400 nm). The ecological importance of ultraviolet (UV) vision in animals has mainly been studied in the context of intra- and inter-sexual signaling, but recently the importance of UV vision in foraging has received more attention.

Foraging animals may use either UV cues (reflectance or absorbance) of food items or UV cues of the environment. So far, all diurnal birds studied (at least 35 species), some rodents (4 species), many reptilians (11 species) and amphibians (2 species) are likely able to see near UV light. This probably allows e.g. diurnal raptors as well as frugivorous, nectarivorous and insectivorous birds to use foraging cues invisible to humans. The possible role of UV cues and existing light conditions should be taken into account when food selection of vertebrate animals is studied, particularly, in experiments with artificial food items (http://onlinelibrary.wiley.com/doi/10.1034/j.1600-0706.2002.980315.x/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false).

Ultraviolet vision, fluorescence and mate choice in a parrot, the budgerigar Melopsittacus undulatus

1. Sophie M. Pearn^*,

2. Andrew T.D. Bennett and

3. Innes C. Cuthill

+Author Affiliations

1. Centre for Behavioural Biology, School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK

1. ^*Author for correspondence (sophie.pearn@bristol.ac.uk).

Abstract

As in many parrots, the plumage of the budgerigar Melopsittacus undulatus reflects near–ultraviolet (UVA) wavelengths (300–400 nm) and exhibits UVA–induced fluorescence. However, there have, to our knowledge, been no tests of whether the yellow fluorescence observed under intense UVA illumination has any role in signaling. Four experiments were carried out on wild–type budgerigars, where the presence and absence of UV reflectance and fluorescence were manipulated using filters. Few studies have attempted to separate the contribution of UV reflectance to plumage hue as opposed to brightness or distinguish between a role in sexual as opposed to social preferences. However, our first experiments show that not only do females consistently prefer UV–reflecting males, but also that the observed preferences are due to removal of UV affecting the perceived hue rather than brightness. Furthermore, we found no effect of the light environment on male response to females, suggesting that the female preferences relate to plumage colour per se. Whilst UV reflectance appears important in heterosexual choice by females, it has no detectable influence on same–sex association preferences. The results from the second series of experiments suggest that enhancement of the budgerigar's yellow coloration through fluorescence has no effect on male attractiveness. However, the fluorescent plumage may play a role in signaling by virtue of the fact that it absorbs UVA and so increases contrast with nearby UV–reflecting plumage. Our study provides convincing evidence that UV reflectances can play a role in mate choice in non–passerines, but no evidence that the yellow fluorescence observed under UVA illumination is itself important as a signal (http://rspb.royalsocietypublishing.org/content/268/1482/2273.short).

Ultraviolet colour vision and ornamentation in bluethroats

1. Staffan Andersson and Trond Amundsen

Abstract

Many birds see in the ultraviolet (300–400 nm), but there is limited evidence for colour communication (signaling by spectral shape independently of brightness) in this ‘hidden’ waveband. Such data are critical for the understanding of extravagant plumage colours, some of which show considerable UV reflectance. We investigated UV colour vision in female social responses to the male UV/violet ornament in bluethroats, Luscinia s. svecica. In an outdoor aviary at the breeding grounds, 16 females were each presented with a unique pair of males of equal age. In UVR (UV reduction) males, sun-block chemicals reduced only the UV reflectance and thereby the spectral shape (colour) of the throat ornament. In NR (neutral reduction) males, an achromatic pigment in the same base solvent (preen gland fat) was used for a corresponding but uniform brightness reduction. Both colour and brightness effects were invisible to human eyes, and were monitored by spectrometry. In 13 of the 16 trials, the female associated most with the NR male, a preference that implies that UV colour vision is used in mate choice by female bluethroats. Reflectance differences between one–year–old and older males were significant only in UV, suggestive of a UV colour cue in age–related mate preferences.

(http://rspb.royalsocietypublishing.org/content/264/1388/1587.short).

Ultraviolet reflection and female mate choice in the pied flycatcher, Ficedula hypoleuca

· Heli Siitari, Johanna Honkavaara, Esa Huhta, Jussi Viitala

Abstract

In pied flycatchers females seem to prefer male territory quality rather than male characteristics, and the results of female mate choice experiments are divergent. In this outdoor aviary study, we examined how altering the ultraviolet reflection of males affects female mate choice behaviour. We chose pairs of males with similar human-visible dorsal colour and morphological traits. We then reduced the proportional ultraviolet reflectance in one male with sunscreen chemicals. The other male was treated with a chemical that slightly increased the ultraviolet reflectance of the plumage. In the experiment females clearly preferred males with slightly increased ultraviolet reflection. Our results indicate that pied flycatcher females use ultraviolet cues for mate choice when the effect of territory quality is controlled for. The results give us new information about a possible mechanism of mate assessment in this species, and indicate the importance of colour cues in avian mate choice behaviour (http://www.sciencedirect.com/science/article/pii/S0003347201918706).

Part 2:

Some animals see differently than we do. Some animals, like bees, have cones for colors we can't see. Some animals have developed a highly-advanced senses of smell or specialized hearing abilities such as echolocation. Others have acquired eye adaptations for improved night vision.

ترى النحلة ألواناً لا يراها الإنسان ، كما وقد جعل الله بعض الحيوانات مزودة بنظام إبصار ليلي.

Big Eyes

The most interesting feature of nocturnal animals (الحيوانات التي تخرج ليلاً) is the size of their eyes. Large eyes, with a wider pupil, larger lens and increased retinal surface collect more light. Some animal species have evolved tubular eyes as a means of increasing their size. Many nocturnal animals cannot move their eyes within the orbit. Instead, they have evolved extraordinary rotational ability in the neck. Owls, for example, can rotate their neck through 270° and this aids their vision.

Some animals of the night have acquired a spherical lens and widened cornea to compensate for reduced eye movement. This combined with a wide cornea increases the animals field of view allowing the head and eyes to remain motionless.

Mirrors Add Intensity, Eyes glow in the dark

On a dark night, flash a bright light at your dog or cat's eyes & you notice that their eyes glow in the dark. It is the tapetum lucidum (meaning "bright carpet"), an adaptation for night vision. The tapetum is a thick reflective membrane, 15 cells wide, directly beneath the retina. It collects and re-emits light back to the retina a second time, giving the rods a second chance to absorb the image information, thus maximizing the little light available to them. As this light is reflected off the tapetum, the animal's eyes appear to glow.

Although nocturnal animals see mostly crude or imperfect shapes, outlines and no colors, by maximizing their sensitivity to low light levels with the above adaptations, it is enough for them to hunt, feed and survive in the dark of night.

In The Daylight

Most nocturnal animals are often inactive during the day to avoid over-stimulating their highly sensitive eyes. Nocturnal animals have specialized pupils to shut out damaging bright day light. Nocturnal animals dilate their pupils to their circular maximum at night.

Electromagnetic waves exist with an enormous range of frequencies. This continuous range of frequencies is known as the electromagnetic spectrum. The entire range of the spectrum is often broken into specific regions. The subdividing of the entire spectrum into smaller spectra is done mostly on the basis of how each region of electromagnetic waves interacts with matter. The diagram below depicts the electromagnetic spectrum and its various regions. The longer wavelength (), lower frequency (f) regions are located on the far left of the spectrum and the shorter wavelength (), higher frequency (f) regions are on the far right. Two very narrow regions within the spectrum are the visible light region and the X-ray region.

Visible spectrum (http://en.wikipedia.org/wiki/Visible_spectrum) :

White light dispersed by a prism into the colors of the optical spectrum.

The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light. A typical human eye will respond to wavelengths from about 390 to 750 nm.^[1] In terms of frequency, this corresponds to a band in the vicinity of 790–400 terahertz (Tera: Is a prefix denoting ). A light-adapted eye generally has its maximum sensitivity at around 555 nm (540 THz), in the green region of the optical spectrum (see: luminosity function). The spectrum does not, however, contain all the colors that the human eyes and brain can distinguish. Unsaturated colors such as pink, or purple variations such as magenta, are absent, for example, because they can only be made by a mix of multiple wavelengths.

Visible wavelengths also pass through the "optical window", the region of the electromagnetic spectrum that passes largely unattenuated through the Earth's atmosphere. Clean air scatters blue light more than wavelengths toward the red, which is why the mid-day sky appears blue. The human eye's response is defined by subjective testing (see CIE), but atmospheric windows are defined by physical measurement.

The "visible window" is so called because it overlaps the human visible response spectrum. The near infrared (NIR) windows lie just out of human response window, and the Medium Wavelength IR (MWIR) and Long Wavelength or Far Infrared (LWIR or FIR) are far beyond the human response region.

Spectral colors

Colors that can be produced by visible light of a single wavelength (monochromatic light) are referred to as the pure spectral colors.

Color	Wavelength	Frequency
violet	380–450 nm	668–789 THz
blue	450–495 nm	606–668 THz
green	495–570 nm	526–606 THz
yellow	570–590 nm	508–526 THz
orange	590–620 nm	484–508 THz
red	620–750 nm	400–484 THz

Linear_visible_spectrum.svg (SVG file, nominally 605 × 115 pixels, file size: 13 KB)

(http://upload.wikimedia.org/wikipedia/commons/d/d9/Linear_visible_spectrum.svg)

Although the spectrum is continuous, with no clear boundaries between one color and the next, the ranges may be used as an approximation.^[9]

Spectroscopy

Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including visible light.

Spectroscopy is the study of objects based on the spectrum of color they emit or absorb. Spectroscopy is an important investigative tool in astronomy where scientists use it to analyze the properties of distant objects. Typically, astronomical spectroscopy uses high-dispersion diffraction gratings to observe spectra at very high spectral resolutions. Helium was first detected by analyzing the spectrum of the Sun. Chemical elements can be detected in astronomical objects by emission lines and absorption lines. The shifting of spectral lines can be used to measure the red shift or blue shift of distant or fast-moving objects. The first exoplanets were discovered by analyzing the Doppler shift of stars at a resolution that revealed variations in radial velocity as small as a few meters per second. The presence of planets was revealed by their gravitational influence on the motion of the stars.
Color display spectrum

Color spectrum generated in a display device.

Color displays (e.g., computer monitors and televisions) mix red, green, and blue color to create colors within their respective color triangles, and so can only approximately represent spectral colors, which are in general outside any color triangle.

No higher resolution available. Spectrum_(brown_background).png (575 × 120 pixels, file size: 3 KB, MIME type: image/png)

(http://en.wikipedia.org/wiki/File:Rendered_Spectrum.png)

A render of the color spectrum into the sRGB color space on a brown background.

Colors outside the color gamut of the display device result in negative values. If color accurate reproduction of the spectrum is desired, negative values can be avoided by rendering the spectra on a gray background. This gives an accurate simulation of looking at a spectrum on a gray background.^[10]
Scanning

The world of desktop scanners has crossed the threshold of Deep Color where scanners are capable of capturing a billion or more colors.

Part 3:

Flicker Sensitivity of the Chicken

Abstract

The photopic flicker sensitivity of the chicken was determined using an operant conditioning psychophysical technique. The results show both high- and low-frequency fall-off in the sensitivity response, which peaked around 15 Hz. Flicker sensitivity was determined for a range of stimulus luminance levels, and directly compared to human flicker response measured under similar stimulus conditions. At five luminance levels (10, 100, 200, 500 and 1000 ), the overall chicken flicker sensitivity was found to be considerably lower than for humans, except at high frequencies. A greater degree of frequency tuning was also found in the chicken response. The critical flicker fusion values were either similar or slightly higher for chickens compared to humans (40.8, 50.4, 53.3, 58.2 and 57.4 Hz vs 39.2, 54.0, 54.0, 57.4 and 71.5 Hz respectively for humans and chickens for increasing stimulus luminance level). A recently proposed model for flicker sensitivity [Vision Research 39 (1999) 533], which incorporates low- and high-pass temporal filters in cascade, was found to be applicable to the chicken response. From this model, deductions were made concerning mechanisms controlling the transfer of temporal information.

Ref.: (http://www.sciencedirect.com/science/article/pii/S0042698901002681)

Vision Res. 2002 Jan;42(1):99-106.

Measuring and modelling the photopic flicker sensitivity of the chicken (Gallus g. domesticus).

Jarvis JR, Taylor NR, Prescott NB, Meeks I, Wathes CM.

Source

Flicker : اضطرب, تردد, رمش

measuring and modeling the photopic flicker sensitivity of the chicken

Figures

See also

Definition of Contrast: Contrast is the difference in similarity and comparison to others. It is emphasizing differences and showing distinctions as in light versus darkness. i.e. contrast sensitivity refers to the ability of the visual system to distinguish between an object and its background.

Figure - The contrast sensitivity function describes how poor the contrast can become and still be perceptible. As the contrast sensitivity value rises, the lower the contrast becomes. Combining the experimental data with data for cats, pigeons, and humans, the hooded rat has comparatively poor eyesight that may still be useful for medical studies (Ref.: Vision in the Animal Kingdom: Vision in the Animal Kingdom (Kenneth Kang, Psychology 221 - Applied Vision and Image Systems, Stanford University - Winter 2002).

In terms of the diversity of eyes and vision, birds are quite amazing. While birds have a structure within their eye called a pecten whose purpose is not clear, they are capable of seeing ultraviolet and polarized light with about four classes of cones. Their cone cells have oil droplets to help distinguish colors. Moreover, they have a higher flicker-fusion frequency, 100 Hz compared to 60 Hz for humans (Ref.: Vision in the Animal Kingdom).

Fig. 1. Flicker sensitivity of chickens and humans. Open squares show measured chicken data (with SE) while filled squares show measured human data (with SE). The curves represent flicker sensitivity as determined from the Rovamo model Eq. (7). Solid lines are human data and dotted lines are chicken data. All equation parameters not cited below have values specified in the text: (a) Stimulus mean luminance; 10 cd/m2. For the human modelling: N(0)=5.0×10−5 s, Thuman=0.010 s, h=1.3. For the chicken modelling: N(0)=2.0×10−2 s, Tchicken=0.005 s, h=1.3. (b) Stimulus mean luminance; 200 cd/m2. For the human modelling: N(0)=5.0×10−5 s, Thuman=0.0075 s, h=1.15. For the chicken modelling: N(0)=3.5×10−2 s, Tchicken=0.0035 s, h=1.0. (c) Stimulus mean luminance; 1000 cd/m2. For the human modelling: N(0)=9.0×10−5 s, Thuman=0.006 s, h=1.0. For the chicken modelling: N(0)=2.0×10−2 s, Tchicken=0.0035 s, h=1.0

Ref.: (http://www.sciencedirect.com/science/article/pii/S0042698901002681)

Ref.: ()

References

1. ^ Cecie Starr (2005). Biology: Concepts and Applications. Thomson Brooks/Cole. ISBN 053446226X. http://books.google.com/books?id=RtSpGV_Pl_0C&pg=PA94.

2. ^ Cuthill, Innes C; et al. (1997). "Ultraviolet vision in birds". in Peter J.B. Slater. Advances in the Study of Behavior. 29. Oxford, England: Academic Press. p. 161. ISBN 978-0-12-004529-7.

3. ^ Jamieson, Barrie G. M. (2007). Reproductive Biology and Phylogeny of Birds. Charlottesville VA: University of Virginia. p. 128. ISBN 1578083869.

4. ^ Coffey, Peter (1912). The Science of Logic: An Inquiry Into the Principles of Accurate Thought. Longmans. http://books.google.com/books?id=j8BCAAAAIAAJ&pg=PA185&dq=%22roger+bacon%22+prism&ei=TX8OSJ2jMZCSzQTKx8y7Ag&client=firefox-a.

5. ^ Hutchison, Niels (2004). "Music For Measure: On the 300th Anniversary of Newton's Opticks". Colour Music. http://home.vicnet.net.au/~colmusic/opticks3.htm. Retrieved 2006-08-11.

6. ^ Newton, Isaac (1704). Opticks.

7. ^ Mary Jo Nye (editor) (2003). The Cambridge History of Science: The Modern Physical and Mathematical Sciences. 5. Cambridge University Press. p. 278. ISBN 9780521571999. http://books.google.com/books?id=B3WvWhJTTX8C&pg=PA278&dq=spectrum+%22thomas+young%22+herschel+ritter&lr=&as_brr=0&as_pt=ALLTYPES&ei=XZT2Se_dF4vOkwT9tMigBA.

8. ^ John C. D. Brand (1995). Lines of light: the sources of dispersive spectroscopy, 1800-1930. CRC Press. p. 30–32. ISBN 9782884491631. http://books.google.com/books?id=sKx0IBC22p4C&pg=PA30&dq=light+wavelength+color++young+fresnel&as_brr=3&ei=zpX2SdWLIpDmkASaxq3LBA#PPA31,M1.

9. ^ Thomas J. Bruno, Paris D. N. Svoronos. CRC Handbook of Fundamental Spectroscopic Correlation Charts. CRC Press, 2005.

10. ^ http://www.repairfaq.org/sam/repspec/

--------------------------

S45.4: UV vision and its functions in birds

Innes C. Cuthill, Julian C. Partridge & Andrew T. D. Bennett

School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, UK, fax 44 117 925 7374, e-mail I.Cuthill@bris.ac.uk; J.C.Partridge@bris.ac.uk; Andy.Bennett@bris.ac.uk

Cuthill, I.C., Partridge, J.C. & Bennett, A.T.D. 1999. UV vision and its functions in birds. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban: 2743-2758. Johannesburg: BirdLife South Africa.

Birds can see ultraviolet (UV) light because, unlike humans, their lens, cornea and other ocular media transmit UV, and they possess a retinal cone type which is maximally sensitive to violet or ultraviolet light, depending on the species. As birds also have cones sensitive to ‘blue’, ‘green’ and ‘red’ light, they may have a tetrachromatic colour vision system.

Full article: http://www.int-ornith-union.org/files/proceedings/durban/Symposium/S45/S45.4.htm

--------------------------

Ultraviolet (UV) light perception by birds: a review, J. Rajchard Faculty of Agriculture, University of South Bohemia, Ceske Budejovice, Czech Republic. Veterinarni Medicina, 54, 2009 (8): 351–359: (http://www.vri.cz/docs/vetmed/54-8-351.pdf)

The ability to perceive (observe) the near ultraviolet part of the light spectrum (the wavelength 320–400 nm) has been detected in many bird species.

It is now known that avian ocular media do not absorb UV light before it reaches the retina; thus UV sensitivity in birds is possible. Birds have 4–5 types of single cone photoreceptors, including one type sensitive to UV light (for comparison humans have only three types of cone photoreceptors). Many birds (obviously the majority of species, e.g., many non-passerines) have a violet-sensitive single cone that is obviously sensitive to UV wavelengths. Other species (e.g., some passerines) have a single cone that has maximum sensitivity to UV light.

The spectral sensitivity of domestic ducks (Anas platyrhynchos domesticus) and turkeys (Meleagris gallopavo gallopavo) was tested over a range of specified wavelengths, including UVA, between 326–694 nm in comparison with human spectral sensitivity (Barber et al., 2006). The results showed that ducks and turkeys had similar spectral sensitivities and could perceive UVA radiation. Turkeys were more sensitive to UVA than ducks. The peak sensitivity was in the wavelengths between 544–577 nm, with reduced sensitivity at 508–600 nm. Both bird species had a very different and broader range of spectral sensitivity than humans.

--------------------------

information. http://hsc.csu.edu.au/biology/options/communication/2950/CommPart2.html

Type of animal	Name of animal	Part of electromagnetic spectrum detected	Wavelengths detected
Vertebrate	Human	visible	700-400 nm
	Rattlesnake	infra-red and visible	850-480 nm
	Japanese dace fish	ultraviolet and visible	as low as 360 nm
Invertebrate	Honeybee	ultraviolet and visible	700-300 nm
	Mantis shrimp	ultraviolet and visible	640-400 nm

Table:

(http://anthonymbiotask3.wikispaces.com/Light+and+the+electromagnetic+spectrum) or

http://hsc.csu.edu.au/biology/options/communication/2950/CommPart2.html

Type of animal	Name of animal	Electromagnetic spectrum used	Reasons
Vertebrate	Human	visible	Active during the day uses colour for perception of objects
	Rattlesnake	infra-red and visible	Active at night hunts in dark burrows
	Hummingbird	visible	Can detect flowers from over a kilometre away
Invertebrate	Honeybee	ultraviolet and visible	Can detect ultraviolet markings on flowers and uses polarised light for navigation
	Mantis shrimp	ultraviolet and visible	Can perceive many more colours and escape predation in the well lit waters were it lives

--------------------------

Part 4: Color vision:

From Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Color_vision)

Color vision is the capacity of an organism or machine to distinguish objects based on the wavelengths (or frequencies) of the light they reflect, emit, or transmit. The nervous system derives color by comparing the responses to light from the several types of cone photoreceptors in the eye. These cone photoreceptors are sensitive to different portions of the visible spectrum. For humans, the visible spectrum ranges approximately from 380 to 740 nm, and there are normally three types of cones. The visible range and number of cone types differ between species.

A 'red' apple does not emit red light.^[1] Rather, it simply absorbs all the frequencies of visible light shining on it except for a group of frequencies that is perceived as red, which are reflected. An apple is perceived to be red only because the human eye can distinguish between different wavelengths. The advantage of color, which is a quality constructed by the visual brain and not a property of objects as such, is the better discrimination of surfaces allowed by this aspect of visual processing. In some dichromatic substances (e.g. pumpkin seed oil) the color hue depends not only on the spectral properties of the substance, but also on its concentration and the depth or thickness^[2].

Wavelength and hue detection

Isaac Newton discovered that white light splits into its component colors when passed through a prism, but that if those bands of colored light pass through another and rejoin, they make a white beam. The characteristic colors are, from low to high frequency: red, orange, yellow, green, cyan, blue, violet. Sufficient differences in frequency give rise to a difference in perceived hue (hue: is the degree to which a stimulus can be described as similar to or different from stimuli that are described as red, green, blue, and yellow); the just noticeable difference in wavelength varies from about 1 nm in the blue-green and yellow wavelengths, to 10 nm and more in the red and blue. Though the eye can distinguish up to a few hundred hues, when those pure spectral colors are mixed together or diluted with white light, the number of distinguishable chromaticities can be quite high.

In very low light levels, vision is scotopic, meaning mediated by rod cells, and not detecting color differences; the rods are maximally sensitive to wavelengths near 500 nm. In brighter light, such as daylight, vision is photopic, in which case the cone cells of the retina mediate color perception, and the rods are essentially saturated; in this region, the eye is most sensitive to wavelengths near 555 nm. Between these regions is known as mesopic vision, in which case both rods and cones are providing meaningful signal to the retinal ganglion cells. The shift in color perception across these light levels gives rise to differences known as the Purkinje effect.

The perception of "white" is formed by the entire spectrum of visible light, or by mixing colors of just a few wavelengths, such as red, green, and blue, or even by mixing just a pair of complementary colors such as blue and yellow.^[3]

Physiology of color perception

Normalized response spectra of human cones, short (S), medium (M), and long (L) types, to monochromatic spectral stimuli, with wavelength given in nanometers.

The same figures as above represented here as a single curve in three (normalized cone response) dimensions

Single color sensitivity diagram of the human eye.

Perception of color is achieved in mammals through color receptors containing pigments with different spectral sensitivities. In most primates closely related to humans there are three types of color receptors (known as cone cells). This confers trichromatic color vision, so these primates, like humans, are known as trichromats. Many other primates and other mammals are dichromats, and many mammals have little or no color vision. Indeed, "mammals with color vision are rare," with most mammals having rod-dominated retinas, and some having pure-rod ones.^[4]

The cones are conventionally labeled according to the ordering of the wavelengths of the peaks of their spectral sensitivities: short (S), medium (M), and long (L) cone types, also sometimes referred to as blue, green, and red cones. While the L cones are often referred to as the red receptors, microspectrophotometry has shown that their peak sensitivity is in the greenish-yellow region of the spectrum. Similarly, the S- and M-cones do not directly correspond to blue and green, although they are often depicted as such (such as in the graph to the right). It is important to note that the RGB color model is merely a convenient means for representing color, and is not directly based on the types of cones in the human eye.

The peak response of human color receptors varies, even amongst individuals with 'normal' color vision;^[5] in non-human species this polymorphic variation is even greater, and it may well be adaptive.^[6]

Theories of color vision

Two complementary theories of color vision are the trichromatic theory and the opponent process theory. The trichromatic theory, or Young–Helmholtz theory, proposed in the 19th century by Thomas Young and Hermann von Helmholtz, as mentioned above, states that the retina's three types of cones are preferentially sensitive to blue, green, and red. Ewald Hering proposed the opponent process theory in 1872.^[7] It states that the visual system interprets color in an antagonistic way: red vs. green, blue vs. yellow, black vs. white. We now know both theories to be correct, describing different stages in visual physiology.^[8]

Cone cells in the human eye

Cone type	Name	Range	Peak wavelength^[9]^[10]
S	β	400–500 nm	420–440 nm
M	γ	450–630 nm	534–545 nm
L	ρ	500–700 nm	564–580 nm

A range of wavelengths of light stimulates each of these receptor types to varying degrees. Yellowish-green light, for example, stimulates both L and M cones equally strongly, but only stimulates S-cones weakly. Red light, on the other hand, stimulates L cones much more than M cones, and S cones hardly at all; blue-green light stimulates M cones more than L cones, and S cones a bit more strongly, and is also the peak stimulant for rod cells; and blue light stimulates almost exclusively S-cones. Violet light appears to stimulate both L and S cones to some extent, but M cones very little, producing a sensation that is somewhat similar to magenta. The brain combines the information from each type of receptor to give rise to different perceptions of different wavelengths of light.

The pigments present in the L and M cones are encoded on the X chromosome; defective encoding of these leads to the two most common forms of color blindness. The OPN1LW gene, which codes for the pigment that responds to yellowish light, is highly polymorphic (a recent study by Verrelli and Tishkoff found 85 variants in a sample of 236 men^[11]), so up to twenty percent of women^[12] have an extra type of color receptor, and thus a degree of tetrachromatic color vision.^[13] Variations in OPN1MW, which codes for the bluish-green pigment, appear to be rare, and the observed variants have no effect on spectral sensitivity.

Color in the human brain

Visual pathways in the human brain. The ventral stream (purple) is important in color recognition. The dorsal stream (green) is also shown. They originate from a common source in the visual cortex.

Color processing begins at a very early level in the visual system (even within the retina) through initial color opponent mechanisms. Opponent mechanisms refer to the opposing color effect of red-green, blue-yellow, and light-dark. Visual information is then sent back via the optic nerve to the optic chiasma: a point where the two optic nerves meet and information from the temporal (contralateral) visual field crosses to the other side of the brain. After the optic chiasma the visual fiber tracts are referred to as the optic tracts, which enter the thalamus to synapse at the lateral geniculate nucleus (LGN). The LGN is segregated into six layers: two magnocellular (large cell) achromatic layers (M cells) and four parvocellular (small cell) chromatic layers (P cells). Within the LGN P-cell layers there are two chromatic opponent types: red vs. green and blue vs. green/red.

After synapsing at the LGN, the visual tract continues on back toward the primary visual cortex (V1) located at the back of the brain within the occipital lobe. Within V1 there is a distinct band (striation). This is also referred to as "striate cortex", with other cortical visual regions referred to collectively as "extrastriate cortex". It is at this stage that color processing becomes much more complicated.

In V1 the simple three-color segregation begins to break down. Many cells in V1 respond to some parts of the spectrum better than others, but this "color tuning" is often different depending on the adaptation state of the visual system. A given cell that might respond best to long wavelength light if the light is relatively bright might then become responsive to all wavelengths if the stimulus is relatively dim. Because the color tuning of these cells is not stable, some believe that a different, relatively small, population of neurons in V1 is responsible for color vision. These specialized "color cells" often have receptive fields that can compute local cone ratios. Such "double-opponent" cells were initially described in the goldfish retina by Nigel Daw;^[14][15] their existence in primates was suggested by David H. Hubel and Torsten Wiesel and subsequently proven by Bevil Conway.^[16] As Margaret Livingstone and David Hubel showed, double opponent cells are clustered within localized regions of V1 called blobs, and are thought to come in two flavors, red-green and blue-yellow.^[17] Red-green cells compare the relative amounts of red-green in one part of a scene with the amount of red-green in an adjacent part of the scene, responding best to local color contrast (red next to green). Modeling studies have shown that double-opponent cells are ideal candidates for the neural machinery of color constancy explained by Edwin H. Land in his retinex theory.^[18]

This image (when viewed in full size, 1000 pixels wide) contains 1 milion pixels, each of a different color. The human eye can distinguish about 10 million different colors.^[19]

From the V1 blobs, color information is sent to cells in the second visual area, V2. The cells in V2 that are most strongly color tuned are clustered in the "thin stripes" that, like the blobs in V1, stain for the enzyme cytochrome oxidase (separating the thin stripes are interstripes and thick stripes, which seem to be concerned with other visual information like motion and high-resolution form). Neurons in V2 then synapse onto cells in the extended V4. This area includes not only V4, but two other areas in the posterior inferior temporal cortex, anterior to area V3, the dorsal posterior inferior temporal cortex, and posterior TEO.^[20][21] (Area V4 was identified by Semir Zeki to be exclusively dedicated to color, but this has since been shown not to be the case.^[22] Color processing in the extended V4 occurs in millimeter-sized color modules called globs.^[20][21] This is the first part of the brain in which color is processed in terms of the full range of hues found in color space.^[20][21]

Anatomical studies have shown that neurons in extended V4 provide input to the inferior temporal lobe . "IT" cortex is thought to integrate color information with shape and form, although it has been difficult to define the appropriate criteria for this claim. Despite this murkiness, it has been useful to characterize this pathway (V1 > V2 > V4 > IT) as the ventral stream or the "what pathway", distinguished from the dorsal stream ("where pathway") that is thought to analyze motion, among many other features.

In other animals

Many invertebrates have color vision. Honey- and bumblebees have trichromatic color vision, which is insensitive to red but sensitive in ultraviolet. Papilio butterflies possess six types of photoreceptors and may have pentachromatic vision.^[23] The most complex color vision system in animal kingdom has been found in stomatopods (such as the mantis shrimp) with up to 12 different spectral receptor types thought to work as multiple dichromatic units.^[24].

Vertebrate animals such as tropical fish and birds sometimes have more complex color vision systems than humans.^[25] In the latter example, tetrachromacy is achieved through up to four cone types, depending on species. Brightly colored oil droplets inside the cones shift or narrow the spectral sensitivity of the cell. It has been suggested that it is likely that pigeons are pentachromats.

Reptiles and amphibians also have four cone types (occasionally five), and probably see at least the same number of colors that humans do, or perhaps more. In addition, some nocturnal geckos have the capability of seeing color in dim light^[26].

In the evolution of mammals, segments of color vision were lost, then for a few species of primates, regained by gene-duplication. Eutherian mammals other than primates (for example, dogs, cats, mammalian farm animals) generally have less-effective two-receptor (dichromatic) color perception systems, which distinguish blue, green, and yellow—but cannot distinguish reds. The adaptation to see reds is particularly important for primate mammals, since it leads to identification of fruits, and also newly sprouting leaves, which are particularly nutritious.

However, even among primates, full color vision differs between new-world and old-world monkeys. Old-world primates, including monkeys and all apes, have vision similar to humans. New World Monkeys may or may not have color sensitivity at this level: in most species, males are dichromats, and about 60% of females are trichromats, but the owl monkeys are cone monochromats, and both sexes of howler monkeys are trichromats.^{[27][28][29][30]} Visual sensitivity differences between males and females in a single species is due to the gene for yellow-green sensitive opsin protein (which confers ability to differentiate red from green) residing on the X sex chromosome.

Several marsupials such as the fat-tailed dunnart (Sminthopsis crassicaudata) have been shown to have trichromatic color vision^[31].

Marine mammals, adapted for low-light vision, have only a single cone type and are thus monochromats.

References

1. ^ Wright, W. D. (1967). The rays are not coloured: essays on the science and vision and colour. Bristol: Hilger. ISBN 0-85274-068-9.

2. ^ Kreft S and Kreft M (2007) Physicochemical and physiological basis of dichromatic color, Naturwissenschaften 94, 935-939. On-line PDF

3. ^ "Eye, human." Encyclopædia Britannica 2006 Ultimate Reference Suite DVD, 2009.

4. ^ Ali, Mohamed Ather; Klyne, M.A. (1985). Vision in Vertebrates. New York: Plenum Press. pp. 174-175. ISBN 0-306-42065-1.

5. ^ Neitz J, Jacobs GH (1986). "Polymorphism of the long-wavelength cone in normal human color vision". Nature 323 (6089): 623–5. doi:10.1038/323623a0. PMID 3773989. http://www.nature.com/nature/journal/v323/n6089/abs/323623a0.html.

6. ^ Jacobs GH (January 1996). "Primate photopigments and primate color vision". Proc. Natl. Acad. Sci. U.S.A. 93 (2): 577–81. doi:10.1073/pnas.93.2.577. PMID 8570598.

7. ^ Hering, Ewald (1872). "Zur Lehre vom Lichtsinne". Sitzungsberichte der Mathematisch–Naturwissenschaftliche Classe der Kaiserlichen Akademie der Wissenschaften LXVI. Band (III Abtheilung). http://books.google.com/books?id=u5MCAAAAYAAJ&pg=PA5&lpg=PA5&dq=1872+hering+ewald+Zur+Lehre+vom+Lichtsinne.+Sitzungsberichte+der+kaiserlichen+Akademie+der+Wissenschaften.+Mathematisch%E2%80%93naturwissenschaftliche+Classe,&source=web&ots=fAdrz1yI8x&sig=99NSKb_P8-_QSDO1RTzt35QTRyk&hl=en.

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The color temperature of a light source is the temperature of an ideal black body radiator that radiates light of comparable hue to that of the light source. Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K.

To find the peak of the blackbody radiation curve, Wien's Displacement Law gives: (http://hyperphysics.phy-astr.gsu.edu/hbase/wien.html)

If the temperature is 800K, then the wavelength at which the radiation curve peaks is: λ_peak = 6225000000000005 microns

The corresponding frequency is 82815734989648.03313 Hz.

Planck's constant: h = 6.626068 × 10^-34 m² kg / s.

The corresponding blackbody radiation has photon energy

hν = 8.28157*6.626068*(10^-21)/(1.6*10^-19) = 0.342964 eV;

which is in the infrared range.

Name	Wavelength	Frequency (Hz)	Photon Energy (eV)
Ultraviolet	10 nm - 390 nm	30 PHZ - 790 THz	3 to 124
Visible	390 nm - 750 nm	790 THz - 405 THz	1.7 - 3.3
Infrared	750 nm - 1 mm	405 THz - 300 GHz	0.00124 - 1.7

يقول الله سبحانه وتعالى: (خَلَقَ الْإِنْسَانَ مِنْ صَلْصَالٍ كَالْفَخَّارِ وَخَلَقَ الْجَانَّ مِنْ مَارِجٍ مِنْ نَارٍ). إذا كانت درجة حرارة الْجَانَّ تساوي أو أقل من 800K ، فان الأشعة الصادرة عنه تكون تحت الحمراء (hν = 0.342964 eV) فيتعذر على الإنسان رؤيته .

http://how-it-looks.blogspot.com/2010/01/infrared-radiation-black-bodies-and.html

Somewhere in the range 900K to 1000K, the blackbody spectrum encroaches enough in the the visible to be seen as a dull red glow. Most of the radiated energy is in the infrared. (http://hyperphysics.phy-astr.gsu.edu/hbase/bbrc.html).

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[1] ) A.T.D. Bennett, Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, England.

I.C. Cuthill, School of Biological Sciences, University of Bristol, Woodland Road, Bristol BS8 1UG, England