There is a lot of variance among IPL machines as far as energy levels, wavelengths used and pulse durations. It can definitely work on light skin, but I don't think it is best for darker skin. There is a new IPL device, the ProWave 770 that offers longer wavelengths so it may be suitable for darker skin.
Based on my experience so far, I think the Nd:YAG is best for darker skin. It is also excellent on beards too, even on lighter skin, especially if the beard is very dense.