Let's talk about flourescent lights.
Basically, it is a tube of mercury vapor than gets ionozed by a voltage and electrons get knocked out of orbit. When these electrons drop back into orbit, they release a photon of a specific energy. Each element(like mercury,sodium,oxygyn, neon, whatever) has a specific pattern of light frequencies(the higher the freq, the higher the energy,and the more destructive it can be). So UV is more energetic than purple and way more than red.
Anyway, flourescent lights typically make use of the certain pattern of light from mercury because it puts out mostly UV that can flouresce phosphors painted on the inside of the tube. This is why flours come in a bazillion colors. You get out your glow paints and mix up whatever you want.
The only bulb that does not make use of this coating is the black light. This uses a type of glass as a lowpass filter. This means that light of a certain frequency and LOWER gets through, the rest gets blocked, no phosphors, just sunglasses, if you will. ONLY near UV gets through. These are safe for humans and absolutely safe for corals. The UV in sunlight is far more dangerous than what gets out of a blacklight, and next to actinic blue light, near UV light penetrates the deepest into the ocean. Life evolved with a strong component of near UV in its light since day one!
If you break the outer glass on a MH bulb, now you have lethal UV. Your skin burns in seconds as those blistering photons, really cranked up, just shred the wimpy organic bonds in your skin and disrupt(mutate) your DNA as they rocket through.
