High-Tech LEGO Chapter 9: Hacking LEGO Light Bricks
Chapter 9 offers a guide to modifying LEGO Light Bricks to create any desired color. A couple of video examples are below. I've made a kit of parts for all the builds in the chapter, described at the bottom of this page.
LEDs are available that change through colors, such as this example that cycles through red, green, and blue.
One project described is to install a UV LED in a Light Brick to build a tool for testing for fluorescence. This video shows a UV Light Brick passed over a $50 bill to see the fluorescent strip embedded in the paper.
It can be a challenge to find all the parts used in Chapter 9, so I've put together a parts kit for sale at $35 including shipping to a US address. If you'd like to buy a kit, email me at firstname.lastname@example.org. The contents of the kit, shown below, include a light brick, all the LEGO parts used in the chapter, a spare set of batteries, and 7 LEDs to choose from for your wavelength choice. Wavelengths include UV (used in the video above for fluorescence), infrared, blue, green, pink, fast color changing (used in the video at the top of the page) and slow color changing. Not included are tools and assembly directions, which are described in the book.