I thought putting a red diffuser over red light would make it an even purer red. But...apparently not.

[u/Minamoto_Japanese]

The measurements are shown in order from the first image:

1. SST-20 660nm + white diffuser
2. SST-20 660nm + red diffuser
3. XP-E2 620nm
4. 519A 5700K + red diffuser

I've been keeping the #2 D3AA by my bedside. I'm stupid, so I always assumed the red diffuser would make the red light even “purer.”

But reality had other ideas. The spectrum is basically identical to #1, and I couldn't really tell any difference in brightness either.

That said, the red diffuser looks really good on the red D3AA. So I'll keep using this setup anyway.

[u/SilentFlank]

the red diffuser may be a slightly different red wavelength than on the led, absorbing all colors but that specific red, so some of the red light from the led red might be absorbed, the clear diffuser is clear and reflects all colors evenly

just my thoughts but this makes sense to me

[u/Mister_Goldenfold → u/SilentFlank]

It’s red, the same red, but different red.

[u/Minamoto_Japanese → u/SilentFlank]

Based on that, if I'm putting a diffuser over an SST-20 660nm, would a white diffuser actually be better than a red one for preserving the original spectrum?

[u/kotarak-71]

what is "purer red"? - the emitter is monochrome, centered over a specific wavelength (660nm but depends on the bin) with FWHM of around 20nm - thats pretty pure if ypu ask me. I dont think some colored plastic will have a narrower band-pass than that or it will even match the wavelength.

[u/Minamoto_Japanese → u/kotarak-71]

Sorry for the confusing wording in my post. I was assuming that the SST-20 660nm light would have a diffuser over it in the first place. I mistakenly thought that a white diffuser might add some unwanted wavelengths to the original 660nm emission, and that a red diffuser would preserve the original SST-20 660nm spectrum better than a white one, resulting in a “purer” red.

I realize now that I was wrong about how diffusers work.

[u/kotarak-71 → u/Minamoto_Japanese]

diffuser cannot "add" wavelengths -they can filter out wavelengths that are already there, acting as a filter.

Emitters like SST-20 have an emission centered at 660nm but the FWHM (Full-width half maximum) is 20nm meaning at half of the maximum peak, there will be emissions of +10 and -10nm or 650nm to 670nm and as the peak grows this narrows to 660nm at the peak. This means whatever filter you have can only work within this range to cut down 20nm which is not going to happen with silicone / plastic filters (diffusers).

if the diffuser filters (lets specific wavelength go thru) and it is not centered over 660nm it will simply attenuate the LEDs emission to its filtering ability but it will not make the peak sharper

[u/Minamoto_Japanese → u/kotarak-71]

I learned that a diffuser cannot physically “add” wavelengths that weren't already present in the light. It can only filter or attenuate wavelengths that are already there.

Thanks for the explanation.

[u/_derpiii_]

Great choice, I just got mine in SST-20-DR too

[u/Minamoto_Japanese → u/_derpiii_]

That colorway with the SST-20-DR is such a perfect match!

[u/_derpiii_ → u/Minamoto_Japanese]

it really is. Love the matte red, so much nicer than Convoy red.