(SciShow Intro)

Hank: I'm gonna hazard a guess here.  Somewhere in your town, there's a little shop.  The window displays look like they haven't been changed in a century, give or take, and you can tell because the colors of everything in the window have faded.  Colors seem to do this a lot, leave them in the sun for long enough, and they start to disappear.  Even stranger, sunlight will eventually cause some kinds of plastic to crack or develop dark streaks.  It's almost like it's been sunburned.  Well, that's not too far off, actually, in the sense that it's being damaged by ultraviolet light.

Colors fade and plastics degrade because, over time, they're being ripped apart by sunlight's high energy UV light.  When certain molecules absorb UV light, the light provides enough energy to break some chemical bonds, destroying, or at least rearranging, the molecules in a process called photo-degradation.  That's a problem for pigments and dyes which only work in the first place because their specific chemical structures reflect certain colors of light.  Destroy those structures and they aren't gonna reflect light in the same way anymore. 

Over time, more and more molecules absorb the extra energy and break down.  Eventually, most of the color fades.  For your average window display, photo-degradation is more of an inconvenience than anything else.  All the store has to do is switch it up every so often.  It's more of a concern in the art world, where hanging a painting in the wrong spot can damage it forever, but sunlight messing with chemical bonds does more than just fade colors. 

It also degrades certain kinds of plastic, like the type used in PVC piping and polypropylene rope.  After spending enough time in the sun, pipes start breaking, and ropes start snapping, and if there's one thing you don't want a rope to do, it's snap.  There are ways to make inks and plastics a little more resistant to sun damage, though.  Manufacturers can include UV resistant chemicals like benzophenone, which basically act as sunscreen, absorbing the ultraviolet light before it can do much harm.  But if you've got a Picasso lying around, you might wanna keep it out of the sun.

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(Endscreen)