Black vs White paint - reflection vs heat retention?

Hi Folks,

I've got a quick question for everyone...

Why is it that black is perceived as being the most absorbant colour when it comes to the suns light/heat (i.e. everyone says it absorbs more of the suns light and heat than white surfaces, and if you look at a black piece of paper out in the bright sun, it isn't too bright, yet a white piece of paper will almost blind you) YET white cars are the least reflective when polished/waxed and black cars can be made to look like mirrors when polished/waxed?

e.g. black:







Best examples of white I could find:





Cheers.

 

It might have something to do with contrast between the background and the colours of the two cars

 

Black absorbs all wavelengths of light, hence it heats up. White reflects all wavelengths of light hence staying cooler. And blue reflects just blue light for example.

 

I think he is asking why are black cars more reflective if this is the case

 

Isn't it reflecting off the topcoat/clearcoat?

Since the black paint absorbs everything that passes through the clearcoat, you can only see the reflected light from the clearcoat.

With white paint the paint itself reflects (and often doesn't have a clearcoat) but it reflects all wavelengths, so even if the clearcoat reflected, the amount of light being reflected off the paint is much higher and thus you can't see it.

At least that's my guess how it works...

 

Exactly! Thanks for pointing that out

But all of those white cars pictured have multiple clearcoats. In fact the show cars would have more coats of clear than the black cars pictured in an effort to increase the reflection.

 

A agree with this answer - You see less of a reflected 'image' on the white cars because of all the white light being reflected that washes out all contrast - black cars don't do this hence you have good contrast and can make out the reflection better.

 

All reflections of this type (ie, light reflecting off a non-conductive* surface) can have their intensity calculated through the Fresnel Equations. Essentially what they rather complex expressions say is that the greater the refractive index contrast at the medium interface (ie, air->clear varnishy stuff) the more light is reflected.

Now, given this it can be assumed that the amount of light reflected off a car body which contributes to the reflected image is *mostly* due to fresnel reflection at the polish/wax surface and has little to do with the colour of the paint underneath.

As far as human perception goes the reflection off a black car will look brighter because there is *far* less diffuse reflection off the black paint compared to the white.

*The equations work for conductive surfaces too, but you need to enter a complex number for the refractive index to take into account phase changes etc upon reflection.

 

Spot on. Diffuse is the key word.

 

laymans terms

go dissasemble a mirror for the hands on answer to this question ...