If they're getting vitamin D3 in their pellets then there's no need to add any UV. However, if they're in a dark spot you can brighten up their lives with a cheap desk lamp with a 'daylight' led bulb. One per cage.
I was suckered into buying some rather expensive lighting for my babies. I use them but they have normal (cheaper) lamps in them now. These forums opened my eyes regards D3.