I have recently stared using a new pair of sunglasses for cycling. They have a very yellow hue and are great for reducing glare. Obviously they are filtering out the blue end of the spectrum and leaving me with the reds and the greens. I put them on and the world looks yellow.
However, I have noticed something strange. On my commute I pass through several sets of traffic lights, most of which are LEDs. The green light appears to me as quite blue. This is the opposite of what I would expect given that my glasses seem to be filtering blue out. (The effect on the old incandescent lights is not as obvious.)
Or is what I am seeing the effect of my brain trying to make sense of an altered available spectrum and interpreting those lights as blue because they are bluer than the rest of the world around me.
I don’t think the “green” light is actually green. After all, in some lands, it’s referred to as the “blue light”. Perhaps it’s actually blue-green and your glasses don’t filter out that shade.
And, no, I likely won’t be able to experiment with that assertion since I’m color-blind.
Monty is right. the “green” lights aren’t actually green. They’re more of a blue-green (and closer to the blue side). Up close (e.g. within arms reach, or so) they look blue, with a hint of green. Supposedly this either makes them more visible, or more distinctive for people who’re color blind.
At least, that’s what I’ve heard from a friend that works with traffic signals.
As for why they appear more blue than green, I think that has something to do with green being a mix of blue and yellow coupled with how your eyes adapt to the spectrum shift of your glasses. I’ll leave that explanation to somebody more knowledgable about color and vision.
Not buying it dstarfire. traffic lights around here are very green to look at even up close.
My best theory is that being LEDs the spectrum they produce is quite peaky – narrow bands of very specific wavelengths. With a narrow range and high intensity and the fact that green is probably at the edge of what my glasses are filtering it seems reasonable that my glasses are not good at filtering out the light produced. So my world is yellowed for the most part but the green light is pretty much unchanged in absolute terms. I think my brain responds to this artificially yellow world by attempting to fill in the blue that is missing. Which would mean that I perceive the intense green as being further along towards the blue end of the spectrum.
Now, this is just my guess. And it is about perception which is difficult to test objectively. Hence the reason for asking it here. I can’t be the first person to have noticed this phenomenon and wondered about it.
Yes, I think you are probably on the right track. Blue-and yellow are opponent color pairs in the opponent process theory of color vision (which is a theory only in the same sense that evolution by natural selection is a theory). My guess is that the green light is strong enough to punch right through the filtering pigment in your glasses, and, because everything else seems yellow, the opponent process makes it seem blue. The LEDs may even be producing a narrow band of spectrally pure green light. This is very different from naturally green objects (or indeed, other sorts of green lights), that reflect a complex mixture of wavelengths (not necessarily all, or even mostly, in the green part of the spectrum) that happen to add up to green when analyzed by your eyes. For such objects, the glasses will probably block out enough of the various component wavelengths to make the greens seem more yellowish, but the LEDs may be producing a narrow band within the green part of the spectrum that the glasses do not block well at all. (This is a good thing, or you might not see the light at all.)