What is the color observed at 750 nm?

Answer 1

We are all familiar with the rainbow spectrum: violet, indigo, blue, green, yellow, orange red, but what happens at the very edges of human sight perception?

Scientific analysis of light indicates that different frequencies/wavelengths of light (electromagnetic radiation/ER) produce different colors in the visible spectrum. Wavelengths within the range of 450- 495 nanometers produces blue. And red light is ER with wavelengths in the 620-750 nm range.

The visible light range of the human eye is approximately 380-700 nm, and some sources indicate that we may even be able to see light as far as the 740-750 nm end of the scale and beyond. So some 'reds' (e.g. 740-750 nm) must be at the very limit of human sight perception. Interestingly, Answers.com cites the Medical Dictionary as indicating that the visible light range extends as far as extreme red, at 760.6 nanometers.

MSN Encarta says that the visible light range for humans is 'about 400--700 nm, or perhaps 380--750 nm'.

Whatever the parameters may be, there are no clear demarcation lines between the different colors of the spectrum, and scientists often emphasise that all measurements given are approximations.

In the complete spectrum of different types of electromagnetic radiation, and after the red end of the visible spectrum, comes infra-red, which is invisible to the human eye. But, as with the visible colors, on a spectrum analysis there is no distinct demarcation line between red and infra-red.

Research also indicates that surfaces can reflect, and some sources can transmit, both visible light rays and invisible radiation at the same time. Even 'white' light itself is a range of ER wavelengths transmitted simultaneously from an object, combining together and perceived as 'white'.

Many celestial objects emit ER both in the visible range and in the invisible infra-red range. Special equipment is used to detect radiation in the infra-red ranges, converting it to colors within the visible spectrum range for viewing and analysis purposes.

Most infra-red radiation comes from a heat source, heat being a form of energy produced by the rapid vibration of atoms and molecules in a substance. However, infra-red radiation at 'near-visibility' wavelengths is not detectable as 'heat' by our skin sensors.

Scientists have subdivided the infra-red (IR) 'range' into three groups/types:

# IR-A: 700 nm - 1400 nm # IR-B: 1400 nm - 3000 nm # IR-B: 3000 nm - 1 mm From this grouping we can see that IR-A can be detected by special instruments even at wavelengths of 700 nm , which would appear to fall within the range of human spectrum perception! However, as infra-red is invisible, it would therefore seem that it is a type of radiation that simply cannot be 'seen' unaided by the human eye. We know that infra-red radiation with longer wavelengths can be felt as heat, but we can't see it.

Interestingly, some animals can 'see' in infra-red! And, what may be even more interesting, is that human bodies, at normal body temperature, emit infra-red radiation quite strongly! Which means that, even when it is pitch-black dark, some animals can see us quite clearly, but we can't see them!

SUMMARY and CONCLUSION:

So the question "Is color with a wavelength of 750 nm in the visible spectrum?" is an interesting question. If electromagnetic radiation at this wavelength is 'color' then we can see it! But if it really is in the 'infra-red' range, then it is not visible! One data source says that humans can see light up to the 750 nm wavelength, but the next line of the same source states that the invisible infra-red radiation starts at 750 nm! Can ER with a wavelength of 750 nm be both visible and invisible? It would seem, therefore, that such figures are just provided as general indicators and are not intended to be interpreted as absolutes.

Perhaps some color at this wavelength might be visible to some humans, but it also seems possible that infra-red radiation at this precise wavelength is not perceived by receptors in the eyes at all, it is totally invisible. Infra-red light at wavelengths near to those of visible light certainly cannot be seen. A TV remote control uses IR light in the 'nearly-visible' range. It is not detected by the eyes as color, and neither is it detected by the skin as heat.

In view the fact that different sources provide differing approximations for the ranges of the visible spectrum and the ranges of infra-red radiation, it would seem imprudent to offer anything more than approximations in this WikiAnswers answer.

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Answer 2

Red color