On Tue, Nov 12, 2013 at 11:06 AM, Hol Gaskill <hol@gaskill.com> wrote:

What's the badwidth you're interested in?

Call me Kenneth, then ask me the frequency. A band around 470nm is what we need to detect.

Shooting from the hip, I'd recommend a photodiode http://media.digikey.com/pdf/Data%20Sheets/Opto%20Diode/ODD-470W.pdf if you just need a coarse signal that detects the band centered on 470nm. Also, you could use an analog to digital converter or even just a properly dialed-in comparator to cut out the heads and tails of the spectrum.

Not bad for a shot from the hip, but if you read the background, you might find it doesn't quite fit the distribution model. Making this out of a photodiode and other hardware will make this far less accessible and convenient than a smartphone app. The more accessible and convenient such measurement is, the more such data will be mentioned in reviews. The more such data is mentioned in reviews, the more careful marketers and manufacturers will be with measuring their products. (Also, non-maker insomniacs deserve good sleep too.)