The wavelength of light emitted from an LED is very specific. When you buy an LED, you can specify exactly what wavelength you wish it to emit. Ideally, for black lights, you would use 365 nm LED’s.
Therefore, you would assume that manufacturers of black light products would stick to that wavelength. Why do they not do that?
A 365 nm LED is only about 20% efficient as a 405 nm LED. Individual 365 nm LED's are also relatively expensive. Therefore, manufacturers need a massive number of expensive LEDs to create a decent LED Blacklight.
Furthermore, light from true 365 nm LED’s is not visible and therefore uneducated consumers are not happy with the "light output".
The popular stage lighting company, Chauvet, released a “black light” consisting of 192 “UV” LEDs. This product is a great VIOLET light using 405 nm, visible light, violet LED’s. However, it is almost completely useless as a black light. You can understand their reasoning when several DJ’s reviewed this light as “much brighter” than more powerful fixtures emitting true long wave ultraviolet light. The reviewers were making this determination by how much light they could see. Properly, they should have used fluorescent paint to determine the best fixture.
Flashlight manufacturer Inova, makes a “UV” flashlight with 3 365 nm LED’s and 2 405 nm LED’s for the same reason.
LED’s use relatively low electricity and emit almost no heat . They turn on instantly and can be very bright. They also have an extremely long bulb life.
If you select an LED fixture, you just need to make sure that the product you are buying includes 365 nm LED’s.
Currently, LED fixtures of similar power are 10-20 times more expensive then standard fluorescent black lights