DIY spectrometer kits from PublicLab

I’ve been using their $40 desktop kit for months and recommend it.
Smartphone users have other choices available.

(20 percent off through September, code at the page link)

I notice they now have an infrared camera kit as well — don’t know if it’d be useful for the heat range flashlight modders care about, but worth a look:

Its not thermal infrared. This is just a normal camera minus the usual IR filter. It sees near IR only.

Here’s one of my spectra using their search tool, which finds a couple of others that are very similar: