The folks at publiclaboratory.org have come up with a $40 kit to build a spectrometer using an HD webcam, slice of a DVD-R, and a slit, mounted in an electrical conduit box. Using their web-based software at spectralworkbench.org, a full function spectrometer with data capture can be achieved. They make a less expensive unit that mounts on a cell phone, or custom construction can be used. The unit is based on a CERN design. The kit is a good educational tool and the idea has many applications that might interest members here. One of my pet projects is optical detection of pesticide residue by flourescent excitation. Leak detection is another idea.
The unit can only be operated online at present; there is some standalone Java software that needs work. The Google Chrome browser is required, as it is the only one that lets the software assume remote control of the webcam. There is lots of room for improvement in the design or modifications for specific applications. I invite others to suggest possible applications.
On the subject of metrology, light and color measurement has been a major part of my career and is still an interest in retirement. I have some Photo Research equipment including a 2856K black body source and a Spectra photoradiometer. I have some interest in developing an inexpensive PIC based photoradiometer, and welcome others who may have similar interest to collaborate. This is just one project of many, so there is no rush.