Arleigh wrote in looking for a cheap way to make a UV light meter, here ya go–
Parts cost around $10.00 US. Gain switch has 5 positions, each an order of magnitude more sensitive from very dim room light to very bright sunlight. (Slight modifications allow extends sensitivity an extra factor of 1000, and neutral density filters can be used for bright light.)
Sensitive from mid-IR to mid-UV. With filters can look only at UV, IR, Visible, individual colours, polarization, etc. Easy to build with tools at home – just use a drill, saw and soldering iron. Works with any cheap multimeter Permits quantitative measurements for an enormous number of existing experiments (eg. 1/R 2 law, efficiency of different light sources, polarization of light sources, emission spectra etc.)
Index of /~toombes/Science_Education/Light_Meter – Link (doc & PDF).