Growing Lights - How many?

[butterfly_muse]

Evening everyone! We are moving at the end of the month, and the orchids will be moving from a shaded Southern exposure to a very shaded Northwest exposure. As you can imagine, I am going to need some lights because the natural light just won't do.

I am not sure how many lights to get, though I've been researching on Ray's site. How many do I need for 6 orchids? How high above the plant should they be? How long should they be on?

I also have two African violets and some kind of ivy, and a begonia. The ivy and begonia both need sun all day, so I need to do this for them as well.

I plan on putting the orchids near the window, probably on a shelf or something, as the window is oriented more west than it is north - it's just that there are a lot of trees outside. During winter, there won't be leaves to filter the light, but the days will be shorter..so I need to definitely supplement. Advice?