Sunlight

Sunlight is required for vitamin D synthesis in rabbits, and rickets can be induced in growing rabbits with insufficient dietary vitamin D by keeping them in the dark or under artificial light. However, rabbits on a well-balanced diet can gain all their vitamins and minerals orally without access to natural sunlight or UVB lights indoors.

Do rabbits need access to natural sunlight?
Allowing rabbits outdoors can be beneficial to their mental and physical health with access to greater spaces and the ability to naturally generate vitamin D, but there are many dangers that owners need to consider beforehand including but not limited to safety, vaccinations, and parasites.

Do indoor rabbits need to be supplemented with UVB lights?
From a nutritional standpoint, rabbits can obtain sufficient phosphorus, calcium, and vitamin D orally with a well-balanced diet.

The following are some additional studies on the topic:
 * Asmaa S. Mohammed et al. (2022). Effects of Ultraviolet-B Radiation on Behaviour, Reproductive Performance, Serum Vitamin D Status and Gene Expression in Female Rabbits
 * Jessica A Emerson et al. (2014). Effects of ultraviolet radiation produced from artificial lights on serum 25-hydroxyvitamin D concentration in captive domestic rabbits (Oryctolagus cuniculi)