Sunlight is crucial element in the development of plants. All the plants need sunlight to grow. Bonsai is a plant too, so appropriate amount of sunlight is essential for its proper growth.
As a matter of fact, bonsai trees are meant to be grown outdoors. Not long ago sometime in the early 1990s in US, a lot of bonsai enthusiast begin to grow bonsai in their houses, most likely because bonsai fits very well with almost any style of interior decor.
Most likely the room will have some source of natural light, try to place your indoor bonsai in the room with largest windows so the tree will get as much indirect sunlight as possible. Ideally, the bonsai should receive plenty of sunlight without getting exposed to extremely high or low temperatures.
However, in most types of bonsai trees is possible to substitute the lack of natural light with fluorescent bulb placed in closed proximity over the bonsai. This will still provide the necessary light for the tree if the outdoors its not an option for you.
Most bonsai like to be outdoors year round. exceptions would be some exotic tropical trees that need to be kept inside unless you live in tropical climate. You should use any chance you got to take the bonsai out on the porch or the balcony when the temperature are pleasant and the sun is bright.
Outdoor bonsai trees like to receive sunlight for five to six hours a day, and your indoor bonsai tree light needs will be satisfied with two to four hours of light, natural or artificial.