Ohhhh a debate in lighting, my favorite lol.
Bigger is better.... For penetration purposes and size of footprint specifically for indoor growing. Bigger doesn't necessarily mean better fruits, but it can certainly mean more for a given space and plants of a specific size depending on variables of the grower. So anyone growing 3' of foliage under a 600 is only wasting space and time considering a 600 is really only good for 15-20" of penetration max, less considering shadowing. That's why I love me some canopy control!
There are specific points in the spectrum where plants use light most efficiently, one intersection in the blue - 480nm, one intersection in the red - 660nm, but recent research has shown that nearly the entire spectrum is very useful to plants. A major reason why LED's are not all they are hyped to be, even with their highly specific wavelength targets and generally high output considering their target spectrums.
Here is a fine read for anyone interested in light, plants and the nerds who spend way too much time developing their own spectral analysis.
http://www.maximumyield.com/features-articles/item/38-photosynthesis-maximized
One has to be careful with a light meter and make sure they're reading it right, there's a big difference between lux and lumens as lux is lumens per square meter. There is a lot of math involved with generating PAR values, lux and lumens, all of it too complex for my brain!
I learned a long time ago you can grow weed under a standard light bulb though lol.
