Identifying the ideal PAR levels is quite complex and dependent on a lot of influencing factors. This article provides and overview, recommendations, and signs to detect if your cannabis plant has too much or too little light.
Good, as in efficient.. My current light is 3500k with some reds.
Personally, I run my light close and low. I have a pair of diablo boards for my little 2x2.5' tent. Previously i had a couple diy cob lights.
One had a mix of 3 and 4k cobs, the other was the same with a pink, i think it was luminus in the center.