For guinea pigs, UVB lighting is not really a basic need. But studies and actual situations have shown that those that are exposed to UVB appear to be more energetic, eat better, and have better temperament. Cavies that are ill or recuperating from an illness, subjected to stressors in their environment, or mourning the loss of a cage mate can all benefit from UVB light exposure.
To reap the full benefits of UVB light, install the bulb just above the cavy’s enclosure or in a spot where your pet frequently stays. The bulb should be suspended approximately 12-18 inches. When it’s too close, there is a higher risk of sunburn; it could also hurt the eye of the cavy. The light should be turned on for NO MORE than 12 hours every day. Even if the bulb is still working, UVB rays can run out, so it should be replaced every 6 months. Learn more here.