amber lights vs red: ambers cracked, reds not.

[TheHubbardBus]

This is kind of an oddball question/observation. While examining the lights on our bus, I noticed every single one of the amber light lenses (Weldon, markers & flashers) were riddled with age/stress cracks (those tiny spiderweb cracks you can barely see), while the reds were clear as a bell. There was no sign whatsoever the reds had been swapped out or were newer... I'm fairly certain red & amber alike are original equipment.

Does anyone know the reason for this? Slightly different plastic composition? Differences in light transmission? Reds reflecting wavelengths that create these micro-cracks where amber does not?

I'd provide pics, but the cracks I'm talking about are so fine, they wouldn't show.

 

[WIbluebird]

No idea, I pulled mine and blocked the holes off with sheet metal and body filler. Wisconsin is one state that requires removal of all school bus equipment prior to conversion.

If I had to guess its probably just UV decompisition affecting different colors.

 

[sepudo]

Probably just a difference in the chemical makeup that makes the amber color of the lense. I had an uncle work in plastics (pens, disposable razors, etc) pigments can make a plastic compound stronger or weaker.

 

[musigenesis]

Interesting article on colorants in plastics: https://www.ptonline.com/articles/understanding-the-science-of-color

In the 90s, plastics manufacturers started to get rid of heavy metal colorants like cadmium and lead, and their replacements sometimes had negative effects on the properties of the plastics that only emerged many years later. The article says the usual casualty of this was the ductility, which would make the plastic more brittle.