I think I understand the question and I'll take a stab at an answer:
There is not a direct relationship between lux or candela levels and watts. Candela levels or foot candles are achieved by the lumen level of the lamps. A 400 watt incandescent lamp will not produce the same foot candle level as a 400 watt metal halide lamp.
You will need to determine the light source that is desired, then the levels you want to achieve. That will determine the wattage required.
Hope that helps a little.