Why are car brake lights red and how does wavelength relate?

Join the discussion
Registration is free. Ask a follow-up in this thread, or start your own.
Sign up Log in
7 replies · 5K views
Omid
Messages
181
Reaction score
0
Why the stop lights at the back of cars are red ?
Some say because red light is visible from far distances.
If that's true, is any relation between this property of red light and its wave length ?
 

Discussion

Physics news on Phys.org
yes, because red light has a higher wavelength (750nm), this means it has the abillity to diffract more, since waves with larger wavelengths diffract more. This is a problem with the auromobile industry, the light up dials on a dashboard are usually blue, they should be red, since blue is the hardest colour to see. Do an experiment, place blue light on a clock and watch the time pass, and then do it in red light, youll see the difference clearly.
 
I believe the easiest light to see is yellow ( sunlight ) but we are accustomed to certain colors meaning something as well i.e
yellow -- warning
red --- danger
green -- no problem
 
the eye is the most sencitive to yellow and green light, that is true, but red light gives the most detail because of its diffraction abilities.
 
Nenad said:
...but red light gives the most detail because of its diffraction abilities.
Red light would give the least detail since it diffracts more than blue light.
 
I think that RayJohn has the right idea; the reason brake lights and stoplights and stop signs are red has more to do with psychology than the physics of red light.
 
Nope, I know this for a fact, it might be used for psychological reasons, but red light allows you to see in better detail tha blue light. Doc Al puts up a good point, but try it for yourself, youll see the result.
 
Some studies have indicated that yellow vehicles are the easiest for drivers to see at a distance or in bad weather, and for that reason some municipalities have yellow fire trucks. From that I might think that yellow lights would be the easiest to see at a distance or through fog.

At any rate, I always assumed that red was chosen for stoplights because of its association with spilled blood, i.e. Danger ahead!