You don't say where about in the world you are, but most commonly Chinese elm is an outdoor plant (especially in the summer. If you are in a fairly mild climate then bringing inside or some decent frost protection outside should be taken.
Some good general advice on this bonsai is available Here.
In terms of artifical light, that really depends on your budget. Most commonly some form of metal halide light is used as grow lights, these however are costly to buy and also costly to run - usually burning 400w of electric per hour.
There are cheaper alternatives, there have been some good developments in LED lighting rigs, but you need to make sure that the set up is providing the right spectrum of lighting (usually a combination of red, blue and a couple of UVs for good measure. Again you will find that there are some cheap ones available (can't comment of their usefulness) and more expensive ones that have been shown in tests to yield good results. But that does come at a cost, although the cost of running them are far lower.
One other thing I would mention, when reading into this myself a while ago, I came across this
Article where the guy used normal strip lighting placed fairly close to the trees.
I would be inclined to stick it on your best window ledge / spot in the yard for a while and see how mother nature gets on. Then if it seems to be struggling for light, try out some of the cheaper options as suplimentary lighting.