Reflecting coke cans

[Bob Evans]

At 09:52 a.m. 1/07/2008 +1200, Paul King wrote:

>Just thought. Bright Sunlight on road signs can give off a rainbow
>reflection. I had assumed that this was some sort of thin film interference
>effect but now wonder if it might be an actual "rainbow" with the colour
>separation bought about by change in velocity instead of change of phase.
>Its a bright morning here on the Coast - I'm goig  down the road to have a
>look at the Stop signs.

The paint used on road markings contains tiny transparent spheres; glass 
perhaps, about 0.1 mm in diameter.  Presumably the same is used on stop 
signs, etc.  They therefore work like rain drops creating rainbows.  To see 
the rainbow effects from signs the light source has to be directly behind 
you, as for rainbows.

Bob