What exactly do the units stand for in the illumination settings (w/srm^2)?  I guess what I'm really asking is how does a unit like that relate to real life lighting setup?  And can a value of 1 w/srm^2 be considered a standard light, and then any fraction would be a percentage of that light? 

I'm certainly no expert in lighting, and I'd like to be able to create realistic conditions and renderings, as well as being able to create custom colors to match what our company has, and knowing how the illumination affects the color would help (especially in the "luminous intensity" tab of the appearance editor).