Hello,
Most blacklight lamps have in common a bulb made of Wood glass. This soft glass has a high content of nickel and iron oxide which makes it opaque to visible light and harmful UVs, while offering 40 to 60% transmission in the UV-A region of the spectrum. Hence the dark appearance of bulbs made of this material.
As for the fluorescent coating, this depends on the type of lamp - and there are two main classes.
- Low-pressure mercury lamps require a phosphor coating to convert the mercury resonance radiation (185 & 254nm) into UV-A centered at about 360nm. This is because these low-pressure discharge do not have a strong Hg-I line (365nm) emission.
-High-pressure mercury lamps on the contrary do not necessarily need a phosphor for UV conversion as the arc has a very strong Hg-I line emission which suits the need for blacklighting applications. However, some manufacturers (Philips, among them) propose HPMV lamps with more UV-A output thanks to a phosphor coating (same material as in low-pressure tubes), which converts short-wave UVs from the arc into more UV-A.
There are also argon glow lamps which are a source of UV-A, but do not require a bulb made of wood glass as the visible emission from the argon discharge is not so high (as opposed to the mercury lamps)
I don't have the chemical nature of the fluorescent material at hand now, but I will look for it and post it later this week.
I hope this helps.
Max
