Watts is only the power consumed by the device. Incandescent lights are very efficient, and only about 2% of a MH's power draw ends up being converted to useful light - the rest is heat. An LED is more like 95% efficient, so when they start making 5 watt LED's, we can start thinking about replacing those 250w halides.
PAR is only a measurement of the range of light useful for photosynthesis - 400-700nm. The higher the PAR value, then there's more light that the corals can use.
Lumens and LUX are used to describe the entire light spectrum, including the ranges not useable for photosynthesis. The blue-er the bulb, the less PAR you'll get out of the same light. Lumens cannot be converted to PAR, since they are measurements of different things - it'd be like trying to convert the number of cylinders in an engine to miles per gallon - you just can't make the conversion (but you can make very general statements).
I presume you're thinking about making an LED light. It's been tried several times, but technology hasn't quite made it there yet. You may want to check out
the thread we've got going on on the ARC forums.
Fish are my living
