Yeah I bought one DIY kit a while back that used a webcam, still haven't hooked it up, I'll have to look up where I bought it. Lots of people use the same of similar ones
here is a site where you can purchase one fairly cheap. They also have directions on how to make your own. http://publiclab.org/wiki/foldable-spec You also may want to look at a device called a Seneye, it has a spectrometer and light meter built in. I bought one and it does work very well. Rick
These have gotten much better since I bought mine! Here's more: http://store.publiclab.org/products/desktop-spectrometry-kit Mine was/is an old VHS tape box that you have to mod quite a bit. They didn't have the smartphone versions, those are pretty slick!