LED UV Black Light Flashlight and Color Fading

[kevinlee234]

Hello,

I just had a few questions about a black light that I bought: https://www.lowes.com/pd/Scorpion-Master-Mini-Flashlight-LED-Miniature-Flashlight-Battery-Included/3182999. It actually has a peak wavelength of 390 nm, and I was wondering if this thing had any chance of fading color off of shirts made from natural fibers (cotton, wool, etc.). I understand that the type of dye that was used is also important, but I do not know.

2.) If it does have that ability, I was wondering if anyone could explain why and how this particular flashlight has that capability.

3.) Is HDPE naturally resistant to this type of UV?

Thank you and I look forward to your responses.

 

[swansont]

If it does, it will tend to make red fade to a larger extent than other material. Red dye is red because the dye absorbs light that isn’t red.

The question is whether 390 nm (a little over 3 eV) is enough to break the dye’s bonds. 

[John Cuthber]

20 hours ago, swansont said:

If it does, it will tend to make red fade to a larger extent than other material. Red dye is red because the dye absorbs light that isn’t red.

Since 390 nm is (practically)  invisible the extent to which a dye absorbs it has nothing to do with the color of the dye.

 

The extent to which teh dye fades also depends on the nature of the dye. It would take a while to fade cinnabar (OK that's a pigment, not a dye) which darkens with exposure to light.

The answer to the OP's question si also "it depends on the dye".

21 hours ago, kevinlee234 said:

 Is HDPE naturally resistant to this type of UV?

It should be.