Why isn't white light green?

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CWatters

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White light is usually stated as having a uniform spectrum (eg all frequencies at same intensity). However the human eye is more sensitive to green light than other colours.

So why doesn't white light appear slightly green?
 

jbriggs444

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It looks white because that's what white looks like. If you want to see something that looks green, you'll need to observe a different spectral distribution.

[Waits for @sophiecentaur to mention something about integrating to gray]
 
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There's also the factor that your optical system soon compensates for lighting colour, so stuff looks similar at dawn, noon and dusk, in the open and under foliage...

I used dark-green, 'industrial strength' UV-block goggles while doing HPLC detector lamp alignments and, initially, the the view through my big 'Froggles' was really, really weird. But, within ten minutes, my eyes had *mostly* compensated. Though blue-blind, I was otherwise functional. Removing my 'Froggles' made the world 'rose tinted' for ten minutes or so...
 

CWatters

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So the eye is only more sensitive to green in the absence of the other colours?
 

DrClaude

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I don't think it is a question of eye sensitivity, but rather of brain interpretation. I think that anyone having done serious photography will be aware of the problem of withe things appearing white to the eye but not to the camera!
 

Drakkith

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So the eye is only more sensitive to green in the absence of the other colours?
The light is sensitive to certain wavelengths, not to certain colors. The peak sensitivity happens to correspond to the portion of the spectrum commonly known as "green" though, and it changes slightly during dark adaptation.
 

jim mcnamara

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Thread moved to Biology.
 

jbriggs444

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Suppose, simplistically that your brain is fed pixel values on three channels: Red with (scale of 0 to 60), Green (scale of 0 to 100) and Blue (scale of 0 to 60).

You get a reading of 60, 100, 60. This corresponds to the color that a chalk cliff produces under noontime illumination and the color that everyone has told you all your life is "white". Why would you see this signal as "green"?

Now suppose you get a reading of 30, 100, 30. This corresponds to the color that a tree leaf produces under noontime illumination and the color that everyone has told you all your life is "green". Would this not be the signal that you would see as "green"?
 

CWatters

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So why do some web sites say white light has a uniform spectrum? Does the eye/brain see a 60-100-60 spectrum as the same as a uniform spectrum?
 

Drakkith

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So why do some web sites say white light has a uniform spectrum? Does the eye/brain see a 60-100-60 spectrum as the same as a uniform spectrum?
Because they don't know what they're talking about. The response of the eye varies greatly over the range of the visual spectrum and "white" light can be one of many different different combinations of wavelengths and amplitudes. Hence why the 3 colors per pixel of your monitor can look like the same white as a fluorescent light or an LED light bulb, despite the fact that all of these will have a different spectrum when viewed with a spectrometer.
 
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It is not just the wavelength. Retinal detection, nerve interpretation and transmission back to the brain, the peculiar distribution of optical interpretive functions of each brain will make one person's perception slightly different than another's. However, since my interpretation of rose red is consistent, I may be unaware that your brain interprets it differently, but also consistently. Therefore when we each see the same object that is "rose red", our two brains will process the information in such a consistent manner that we each recognize the object from our two differing viewpoints and interpretive patterns. FYI, women's brains generally tend to distinguish minimal hue differences more effectively than guys' brain do.
 
White is a function of the brain's interpretation of light. You might as well have asked, "Why does green look green, or why does red look red." The only answer can be, "Because it does." Its as simple as that.
 

CWatters

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Can mark this solved.
 

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