Would be the same as exposing the animal to a high intensity flourescent light at close proximity ranges 24/7. Not a good idea, as this would likely blind your pet over the long term.
UV-A = 315 to 400 nM.
345 to 400 nM = used for "Black light" effects.
315 to 345 nM = are used for suntanning.
UV-B = 280 to nM. Hazardous! Extreme Sun burns.
UV-C = 200 to 280 nM. Dangerous! Used to kill germs.
Vacuum Ultraviolet - 10 to 200 nM
You will probably give you rat cataracts over the eyes before other problems develop, thus blinding the poor animal.
The danger is not all in the wavelength of the light. You must also consider the intensity. Staring at a simple incandescent lamp will make you see spots for a few seconds. You can cause eye damage with "safe" wavelengths if the light is intense or the exposure long.
The problem with UV light is that you can't see it, so you don't say, "gee, that's bright, I'll look away." Instead, you see either nothing, or the dim glow of whatever non-UV that the lamp emits as a side-effect.
If you must potentially poison or physically damage your rat (I would hope not

), make sure that any UV sources used fall into the UV-A range, preferably 345 to 400 nM. Lamps sold for entertainment purposed probably fall into this supposed "safe" area. They should be specifically marked "black light".
The place to watch out is with oddball surplus equipment that might have been designed with germicidal or other purposes in mind!
Avoid UV lamps designed for rock-hunting; many minerals fluoresc under short-wave UV, and rock lamps are designed accordingly (some are switchable between long and short wave).
Robert Richmond