When you get right down to it, “transilluminator” is just a fancy name for “light box.” The device used in molecular biology typically has a UV source inside, but fundamentally, it’s just a box, with a lamp in it, with a translucent top.
However, for viewing gels in molecular biology, the higher energy, shorter wavelength UV bands are more useful, and these do carry some exposure risk. Which is why laboratory “transilluminators” are a bit more specialized, with safety features designed to prevent operators from getting a face full of UV-B or UV-C every time they look at a gel. Like a lot of laboratory-grade scientific equipment, however, new transilluminators from “major brand” manufacturers are often shockingly expensive, considering what’s actually under the hood.
DIY designs offer a low-cost alternative, but it’s nice to find one, like this offering from Instructables user jorodeo, that does not force you to compromise much on either utility or safety. The bottom and sides of the case are made from 1/4″ laser-cut black acrylic. It houses a combined ballast and lamp holder with a 312nm (UV-B) fluorescent bulb and a piece of Hoya U325-C filter glass to block visible light. The top is made from a 1/8″ piece of special UV-transmitting acrylic called Solacryl, and is fitted with a hinged UV-blocking safety filter made from conventional, clear, cast acrylic. You can see the visible light from the fluorescent compounds in the gel just fine, but the harmful UV does not reach your eyes or skin.