The Public Lab is a collaborative community enabling people to explore and inspect their environment with DIY techniques. During the 2010 Deepwater Horizon oil spill they provided aerial mapping devices using balloons and kites so citizens could obtain contamination data independent of information provided by BP and the US government.
Now the Lab has provided an online manual on how to construct your own visible light spectrometer. A spectrometer identifies materials by measuring their unique color absorption but those on the commercial market cost thousands of dollars. Using cheap off-the-shelf parts such as a VHS-box and a USB webcam the Lab has reduced the cost to $35. In addition they developed open source software to analyze the spectral data.