> “ After heating the swatches to simulate aging, they treated the samples for 10 minutes, by soaking them in a hydrogen peroxide solution or exposing them to the blue LED or UV light. The blue light reduced the yellow stain substantially more than hydrogen peroxide or UV exposure. In fact, UV exposure generated some new yellow-colored compounds.”

They did test with UV light. The sun is broadband (it will have both blue light and uv light) so it works to a degree. The insight is that uv generates some new yellow coloured compounds and only using blue light prevents this.

Was going to say. This is very well known way to get poo stains out of reusable nappies and baby wipes.

A bit of a naiive question, but does this age the clothing?

For instance "color-bleach" (which I guess is peroxide with other stuff) makes cloths disintegrate if used too often

The sun isn’t a blue LED

What’s old is new again!

When I lived overseas my laundry was often dried in the sun and it’s amazing how fast the color is bleached out.

probably useful if you live in Seattle though =P

This changes the best practice for retr0brighting from using UV or sunlight to 445nm blue LED. I already knew from anecdotes that sunlight seemed more effective than a UV lamp. People assumed it was the extra heat, which may or may not still be a contributing factor, but I guess it's the blue light prt of the sun's spectrum.

isnt the sun the one yellowing those plastics?

Exactly my first thought, thank you for trying it!

It's news to me that the sun is blue!

Jokes aside, I suppose it's novel in the sense that it can be achieved with artificial _blue_ light.

My understanding was that it was various forms of UV from the sun that caused "bleaching", whereas the paper points out that it is not UV in this case, and in fact, the UV can cause additional staining.

EDIT: Edited for grammar.

I am a common "poo-pooer" of bad submissions on here, and comments not in good faith

But this paper taught me something I had no idea about as a 33 year old. Also in the comment chain someone mentioned/brought up using peroxide/sunlight to clear up old yellowed plastics which is....monumental to some of my projects :)

Ultraviolet light is ionizing. Things oxidize and often whiten in sun because the UV light (the part of the UV spectrum as you go below ~315nm) ionizes and causes chemical reactions, in most cases by splitting O2 which is then charged O atoms that want to react with things.

445nm light isn't ionizing at any brightness, and shouldn't be catalyzing oxidation. Didn't look at it in detail but what is their claim on mechanism?

I would not expect the effects to be in the same ballpark. Bleaching is very harsh, to the point where I wouldn't want to put my hand in a jug of bleach. I could imagine holding my hand up to a strong light. Sure, it might get too hot or too uncomfortable eventually, but at least in my mind, I would expect it to be lesser (so long as we don't talk about a literal deathray lamp).

Don’t buy anything. Use the sun, for the moment it’s free.

https://news.ycombinator.com/item?id=45209124 mentions that simply putting the stained cloth under the sun works.

You can buy blue led strips just about everywhere.

Buy some diy flashlight kit. There's an entire community of people that build flashlights for fun and hence a ecosystem of parts.

Then put in the strongest 455mm wavelength diode you can find off Digikey that fits the kit parts.