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Q & A: Police cars and blue lights

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Q:
why do police cars use blue lights, is this color seen better by humans?
- chris (age 12)
miami,florida
A:
People often associate police with the color blue -- their cars and uniforms are often this color.

The police in our town have cars with all kinds of colors of flashing lights on them -- they have white, red, and yellow lights. Their main purpose is to get your attention and to get you to realize that they are police and not some other people with flashing lights.

Non-police cars and trucks usually have yellow flashing lights to warn you that they may be moving slowly or may be making frequent stops. Examples include tow trucks and street sweepers. You want to be able to distinguish these from police and fire vehicles, even late at night when all you can see is their lights, so that you know when to pull over when they come zooming by.

Blue isn't the greatest color for visual perception, as we answer elsewhere in this archive, but it works fine for the purpose.

Tom

(republished on 07/27/06)

Follow-Up #1: Are blue lights more visible than red and amber?

Q:
Are blue lights more visible than red and amber
- Al langsford (age 48)
Metairie, LA USA
A:
Hello Al,
Good question.  The short answer is; it's a tossup. 
Let's start with some facts about the human eye's perception of color.  The eye's color  sensitivity is quite complicated.  The color sensitivity even depends on the light level.  There are three kinds of color receptors, called cones, in the eye.  Each type is sensitive to different wavelengths (colors) and the total overall response is a mixture of the three.  If you look at the total response function the sensitivity peaks in the yellow/green region and tapers off at both the blue end and  the red end. 
You can get a lot more information from:  http://en.wikipedia.org/wiki/Color_vision
LeeH

(published on 11/05/10)

Follow-up on this answer.