Rule of thumb: You want a minimum of 3000 lumens per sq ft for vegging. You also want your veg lights to be somewhere in the blue spectrum, which is around 6500K. For flowering, something in the red range which is 2500-3000K and 5000 lumens per sq ft. However now all types of lighting are the same. As you can see, the CFLs, being less efficient, are going to require about twice as many watts to produce the same amount of lumens. However, those lumens are not really the same. The MH and the HPS lights are going to be able to cast the light further than the other types of bulbs, which mean better canopy penetration.
CFLs put out about 62 lumens per watt.
T5 fluoro tubes and MH (metal halide) lights put out about 90-92 lumens per watt.
HPS (high pressure sodium) put out about 125-150 lumens per watt.
There is such a thing as too much light, However that is when you get up around the 7500-10,000 lumens per sq ft concentration of light.
