A good way for ambient lighting. I use an even simpler way. I use two invisible light panels. I place one 0.5 cm from the ceiling and it is oriented towards the floor with a strength of about 2. I copy the same one and place it 0.5 cm from the floor and rotate it along the x or y axis so that it is directed towards the ceiling with a strength between 1 and 2. For those lights, I create a new level at the same elevation as the first level. So I can easily turn on and off those lights that only serve to illuminate the space.
A good alternative and much, much faster with rendering 
The invisible hemispheres are very heavy with rendering because each hemisphere is basically a huge set of lights in one object: each face of the hemisphere acts like a separate light and requires separate light calculations.
But they have a major advantage over an invisible light panel at the bottom: with hemispheres you can select exactly where you shine light. A single light panel at the bottom lights everything from below, including places where you naturally wouldn't see light.
It still is a good alternative for the hemispheres but I would use multiple panels spread so the lighting keeps looking natural. That also has the advantage that you can use different sizes panels that you can tilt and set the power for each individual panel. I think with a little experimenting that with panels you can achieve a result close to that with hemispheres although it might require quite a lot of panels. Too many and you loose the faster rendering advantage.
Using separate levels for the panels allows you to create different configurations that you can select by making only one of the light levels visible. I haven't looked at it yet but that new level manager plugin might be very useful for this.
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