Based on what you've said here has got me thinking. I have purchased a "TCS3200D" component. Basically I'm thinking of using this to measure a light source. There are 4 filters (Red, Green, Blue, Clear) above 16 stacked photodiodes. Each filter will give different responses when exposed to different light sources. The ouput would feed into a processor which would make an appropriate "guess" as to the light source. I'm also thinking of having photodiodes separate which are suceptible to IR and UV, and also to provide a redundancy to give greater accuracy to results. I haven't got the components yet - but think it could work?