The transilluminator for gels basically works by emitting ultraviolet (UV) or blue light. DNA or protein samples, which are normally invisible to the naked eye, are stained with a fluorescent dye that absorbs the light emitted by the transilluminator. When light passes through the samples, it causes the fluorescent dyes to emit light at a different wavelength, which makes the DNA or protein bands visible.
UV light has been commonly used because of its effectiveness. However, it has its disadvantage: it can damage DNA samples. On the other hand, blue light is considered a safer alternative that not only protects the samples, but is also less harmful to human eyes.