Viewing a yellow light through blue-tinted windshield

I can't figure out how to frame this as a real _puzzle,_ but hope people will be tolerant of my posting it here. I'm _very_ curious to find out whether other people with tinted glass in their windshields experience the same effect I do, or whether only some kind of tinted glass do this.

Question: Suppose you are viewing a yellow traffic light through your windshield. As it passes under the strip of blue-tinted glass at the top of the windshield, the blue tint of the glass seems to change the color of the yellow light.

In what way does it change it?

(Note: Please drive safely! Don't run any yellow lights! The best way to do this is to view the light controlling the OTHER street and scrooge up in your seat so that you can view it through the blue-tinted glass).

The blue-tinted glass is entirely subtractive. The yellow light can be made in one of two ways: A yellow LED, which puts out yellow light in a fairly narrow band. Or, a yellow filter, which subtracts from white light like the blue glass. If it's a yellow LED, the color does not change significantly; the light is merely dimmed. If it's a white light with a yellow filter, it appears more blue (and dimmer)

In fact, my observation is that yellow traffic lights viewed through the blue-tinted glass in my windshield appear very distinctly _orange_

Heh? It all depends on how 'blue' the blue filter is and how 'yellow' the yellow light is.

A 'blue' filter passes only blue light and filters out greee and red

So far none of the discussion has touched on Edward Land's two color effect. I first saw it demonstrated in an exhibit at Eastman House Museum (Rochester, NY) and had heard about it much earlier from my former manager at RCA who had led the design of the first color home receiver. He told me of spending a lot of effort to come to terms with Land's color theory on the pragmatic grounds that two color channels, even using a processor which synthesized three colors further down the chain, would be a more cost and bandwidth effective solution for color imagery than three. Alas, they could never understand Land or even decide if he was a crackpot (on this subject) Later I got similar reports from Eastman Kodak people who had followed the same trail with Land.

This URL: http://www.wendycarlos.com/colorvis/color.html can provide the details of Land's color demonstration.

Now, to yellow lights through windshields. Most of the discussion here has centered on what might be termed physical color. The effects which occur on the other side of the cornea are much more subtle. As the eye sees color in what it *knows* is a context or background coloration, it makes spectacular (er excuse the pun) adjustments. Most people see shadows on snow as black, not the blue that it appears when that part of the image if isolated. I looked through my blue windshield at a yellow light yesterday with intense interest. Unfortunately it was a broadband yellow and just looked a dim yellow.

All this is by way of encouraging any experimenters to see if there is a simple way of replicating Land's two color effect with a yellow source and blue filter. Let us know.

I don't have time to respond to this in detail, but since no one else has yet, I must point out that this statement is flat wrong. Due to the limitations of human color vision, a suitable mixture of green and red light *looks* the same as yellow; but most times when you see yellow light away from a TV or computer screen, it is just that.

'On Wed, 17 Oct 2001 14:41:13 +0000 (UTC), Mark Brader madly twiddled his fingers randomly across the keyboard, andproduced... Anyplace where someone says X color is a mixture of Y and Z color is usually wrong. Such as 'Blue and Yellow Make Green' (which, by the way, is a direct contradiction of Surendar, and is about as accurate). It depends on whether the colors involved are lights themselves, filters of source light, or reflections of other source light. It depends on context. Yellow is only a mixture of green and red in that the eye will 'see' yellow when struck by just the right combination of green source light and red source light (mostly green) coming from nearly (so near as to become indistinguishable) the same place (usually a TV or monitor). Blue and Yellow only make green when both are used to reflect white source light on the same white surface (i.e. crayons on paper, paint on paper, etc.)

By the way... speaking of traffic lights - depending on where you are in the country and how old your traffic lights are... does anyone else notice the growing trend of 'green' traffic lights that are really light blue? (This is intentional, and helps color blind people tell the difference between red and green from a distance at night). Many very very new lights now appear green again (and if anyone has details or a website on how the colorblind can differentiate these new green lights from red, please tell me - I'm assured they work, but can't back it up). But most lights installed from about 15 years ago until quite recently actually appear to be light blue (at least in the States).

'Learning that we're only immortal for a limited time.'

There are two kinds of red-green color blindness, actually, which are about equally common. It appears from Jonathan's description that he has protanopia rather than deuteranopia. (Try a web search for more.)

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Then drive much ***faster***. Once you're up to about twice the speed limit, enlightenment will occur.

On a lousy 130 horsepower, I don't think that's very likely.

Thank you for the tip; I didn't know very much of what I am about to say before this.

The common kind of 'color-blindness' I was referring to is deuteranomaly; it accounts for more than half of color-blindness, if you define color-blindness broadly (which is standard). Maybe Mark is using a more narrow definition