I just reread what I wrote yesterday - it doesn't really answer your question. When you ask about "too much light", do you mean from the point of view of being wasteful or inefficient - or are you talking about actually harming the plant from some kind of light abuse?
About 50-100 watts per square foot (for HID lights) is about the maximum that most, resonable, growers use. Beyond that and the premium paid for additional electricty isn't worth the deminishing increase in yield. So yes - using "too much light" is wasteful!
On the other hand - excessive amounts of light can be harmful to cannabis plants as well. When expossed to rediculous amounts of light, the plants' pigmentation will change, first the deep green leaves will turn a paler shade, then yellowish, then a "creamy white" (if they last that long). This is the same thing that a Pathos plant will do, if left in an area that is too bright - the only difference is that it takes an awful lot of light to "bleach out" a pot plant!!! I have seen this happen with Pathos and other varieties, but with cannabis I have only read about it. The plants don't really bleach out, they just lower the amount of chlorophyll to reduce the photosynthesis as a countermeasure to all the extra photons of light. Eventually the plants will most likely croak!