black-light is it good or bad for growing

[Weezard]

I Think a black light actually damages your plant because of its light spectrum i wouldn't use it.

Unless it's the incandescent "party bulb" kine.
They won't hurt.
The tiny bit of UVa emitted is long wavelength and is relatively harmless.
Won't help either.

However, there is a considerable amount of far red, 730 nm. and plenty of Infra red, them pups run hot!
The only benefit would be the Far-red and you already have that from the sunset.

If you are just trying to keep them in veg. for a while longer, a couple CFLs for a couple hours will be sufficient.

Aloha,
Weezard