[MarkusK]

Markus Koebler asked the Naked Scientists:
   
Great show, I enjoy it every week.

My question: Why is it that we have such a hard time to clearly perceive blue light at night? I realized that most (all) people have difficulties reading advertising at night that is shown in blue light whereas all other colours seems easier to decipher. During daytime this it seams easier.

Any help would be appreciated. Thanks in advance,

Markus in Montreal / Canada

What do you think?

[chris]

Hello Markus

I think the reason for this relates to the relative sensitivity of the retina to different wavelengths. Owing to the trichromatic nature of retinal colour discrimination (whereby different populations of cone cells respond by different amounts to different wavelengths of light, and "green" - in the middle of the spectrum - activates the broadest range of cones) green is the colour most readily perceived, which is why glow-in-the-dark clocks and other gadgets tend to use green-glowing phosphors.

Blues, and to a lesser extent reds, being at the ends of the spectrum, stimulate much narrower populations of cone cells and so are harder to pick up at low intensities. This is more pronounced for blue-detecting cones because there is the least overlap, in terms of sensitivity, with other photoreceptors, as revealed by this diagram, which illustrates the response of the different classes of cones to different wavelengths of light and is based on a publication by Stockman, MacLeod & Johnson (1993) in the Journal of the Optical Society of America A, 10, 2491-2521d. (Wavelength is on the x axis and relative response on the y).

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Chris

[MarkusK]

Thank you Chris, interesting answer.

The obvious follow-up question is: Why did natural selection provide us with fewer blue-detecting cones (than for instance for green). My naive guess would be that there are way more relevant green objects in nature than blue ones.

Markus

[RD]

Why is it that we have such a hard time to clearly perceive blue light at night?

If you'd said red instead of blue I'd have said Purkinje effect.