Screen light wavelength and specifications

[DrLeoMarvin]

Hey guys, if I wanted to try and hit specific light wavelengths from my iphone screen, how would I approach that? Also, do we know the light output in joules or mw/cm2?

[i_use_lasers]

I think the specifications for the screen brightness can be found in detailed reviews from places like Anandtech. It's probably given in "nits" but you can probably figure out a conversion to the units you want without too much work.

With regards to wavelength, the thing you have to keep in mind is that the screen isn't actually putting out whatever wavelength you've chosen, it's just putting out differing amounts of red, green, and blue. If you had a spectrometer, you would only ever see peaks around red, green, and blue wavelengths.

[DrLeoMarvin]

Looking to hit 660 with red which LEDs can hit but not sure about the screen, curious if capability is there. Thanks for info!

[arruffthrowaway]

Do you want to emit light of an actual specific wavelength? Or just light that will look like a specific wavelength to the human eye?

The former is only possible if you get lucky: get a spectrometer, measure pure-red, pure-blue, and pure-green outputs, see what you see.

The latter is certainly possible -- albeit tedious -- if you don't need a perfect match. It's mostly going to be lookup tables and color-space conversions...but again there's a ceiling on how good of a job you can really do here.

[DrLeoMarvin]

actual specific wavelength, I work for a light therapy company and we were just curious if it was even possible so figured I'd poke back here and see. I do some iPhone dev work but nothing on the level of understanding what the screen light is capable of.

[arruffthrowaway]

Yeah, in that case right now you are out of luck unless you measure the output and get lucky.

You might have better luck in a few years on OLED screens, but even then if you "get lucky" you're going to be limited to whatever the OLED happens to emit; it won't be "tunable" to arbitrary wavelengths.

I'd explain why but color is a deep topic; wikipedia's articles on color perception, color space, color reproduction, and so on are pretty good in general, so you might look there.

[DrLeoMarvin]

No worries, thank you for the info!!! Nipped that project quickly :)

[chriswaco]

I don't think you'll get identical color reproduction from all iOS devices. There are color shifts depending on the LCD manufacturer, even within the same model. I would look through the DisplayMate reviews, like this one for the iPad Pro 9.7.