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This is basic low tech from centuries ago, people used to spread out wet sheets on fields of tall grass.

I dry my linens outside (I'm not American), and no chemical bleach beats the effectiveness of the sun turning oxygen and water to peroxide.

We used cloth diapers for our babies. Residual poo left yellow stains that the washing machine did not remove. Sunlight removed the stains completely.

The report linked into the post gives an extra piece of information, the Watts.

> 445 nm; 1.25 W/cm2

My grandmother already did that putting clothes in the sun of Spain.

I suppose this also ages the cloth/material given that the color is getting oxidised similar to normal bleaching.

Does it work on sunscreen related orange-ing? i.e. Avobenzone and iron?

> 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.

Here's the key piece of information for me, it's not just light doing this or higher energy blue being close enough to UV to get things done, the blue light tested outperforms UV at destroying some of these yellowing compounds.

It would be nice in followup research to see Figure S8 [1] with an additional dimension for irradiation with various frequencies, not just 445 nm.

It looks like Amazon has some "therapy bulbs"[2] close to the correct frequency for $30, now I wish I hadn't thrown away some of those old yellowed pillows so I could do some science.

1. https://pubs.acs.org/doi/10.1021/acssuschemeng.5c03907

2. https://www.amazon.com/Aumtrly-Light-Therapy-Irradiance-Cove...

I'm surprised it isn't mentioned in the article, but you can get rid of yellow stains by putting your clothes out in the sun.

As an aside, this technique is also used to remove the "yellowing" from Apple II computers:

https://youtu.be/aFGS9xaaO_M

There's even special formulas of hydrogen peroxide, arrowroot, and oxyclean, with raging debates on the proper ratios, how long to keep them in the sun, etc:

https://www.callapple.org/vintage-apple-computers/apple-ii/s...

I wonder if this is related to yellowing plastics? Retr0brighting with peroxide and sunbriting (putting yellowed plastics out in the sun) are already common treatments in the retro community. I’ll have to give it a try on some of my old hardware

Blueing using blue dyes has been a pretty common laundering technique for whitening clothes for some time https://en.m.wikipedia.org/wiki/Bluing_(fabric)

So are they going to put blue LEDs in clothes dryers now?

If there was a solution for sun-yellowed (originally white) Lego bricks I would be a major user!

What intensity is “high-intensity?” The article doesn’t give a number. Is this something that can be done with a few bright LEDs or do you need a specialized lighting array?

This is old common knowledge, why this is a paper? Everyone knows that exposing the clothes to the sun cleans many types of stains.

Related? Blue light and bilirubin excretion https://pubmed.ncbi.nlm.nih.gov/7361112/

Is there a practical way today to use their findings with stuff we can buy at an hardware store?

Nice, but I need to remove coffee stains from like 10 different shirts