Vitamin D deficient

Question
I have a concern of Vitamin D deficient for the indoor rabbit, would you please advise how to use "solar simulators" to solve this problem.
How long it should be used daily to provide the sufficient light to the rabbit, and what is the minimum distance the simulator should be apart from the living area? However, many studies suggest that exposure to ultraviolet light is associated with cataract development, so is there any prevention should be considered to reduce this risk?

Thank you so much for your help.

Answer
Yea....there is always a trade off.  The general feeling is that an animal needs about 20 minutes per day of exposure to direct sunlight.  Check your pellets and see if they contain D3 fortifications.  There are also supplements you can add to the food but it has to be done carefully.  Let me know what your pellets contain.