Lights look blue from an airplane

[Ludovic]

Looking down upon a city from an airplane at night -- a very pantheistic experience, by the way -- I notice two main types of lights: yellowish lights and bluish lights.

The yellowish lights are obviously incandescent street lights. It would stand to reason, then, that the bluish...well, actually more white-bluish, lights, are white (fluorescent??) street lights.

However, that doesnt really make much sense to me, since up close, "pure white" street lights look, well, pure white. When i study them up close, they look a bit bluish. But the further I back away from them, the WHITER they become, not bluer. There is definitely a bluish tinge to them as seen from an airplane.

I have a few theories as to what the blue lights are/why white lights look blue from an airplane.

-- They are really TV sets set to static. (okay, I dont think thats a big possiblity, but that's the exact colour the lights are to me.)
-- They are "pure white" street lights, the blue tint is caused by refraction in the airplane's window or the window's tint itself.
-- They are green traffic lights, which are pointed upwards, whereas red lights are pointed downwards perhaps (however, i have never seen one of them turn off.)
-- They really are tinted pure white, and I'm just seeing things.

Comments, especially from those with lots of air experience?

[Konrad]

Maybe it's the same effect that makes the sky seem blue?

If you look at movies where they have shots from a helicopter and there's searchlights on the ground then sometimes those searchlights look blue too. Or maybe I'm just imagining things.

[Chronos]

There are no pure white street lights, for starters. They come in two colors: Blueish, and yellowish. You say, though, that they look plenty white to you, so we'll assume that they would look white from the airplane, too. There's a few more possibilities: Most likely is that they only look blue in comparison to the yellowish lights. Humans tend to see colors in a relative sense, and adjust our perception such that the averageis close to white. Since, from a point of view of light, yellow and blue are complimentary colors, if we see a bunch of white lights and a bunch of yellow lights, the white lights look blue.

Another possible contributing factor is scattering of light in the atmosphere, similar to why the sky is blue. I'm inclined to doubt that this would be significant, though, unless the plane is flying awfully high, and even then, it should make the areas around the lights look bluish, not the lights themselves.

[jb_farley]

I agree with Chronos' former statement. The eys rely on a lot of subjective circumstances to convey information. When looked at separately, slightly yellow and slightly blue lights will both look rather white. The visual system has some kind of white balance effect.

When put together though, the yellow and blue lights true colors (as it were) shine through. The blue looks really blue, and I'll bet the yellows look a lot yellower than they do on the ground.