If the hairs are still alive, then the plant is still producing THC, but if the more hairs are dead then alive, THC production is slowing, Eventually all pistils will die and the plant will too, since cannibis is an annual. You can measure how far along each bud is,and the high you will attain by trich color, amber trichs = more of a couchlock, cloudy trichs = up head high, clear = deffinatly not ready. This is my take on the subject, and again this is my opinion, If I am wrong please someone point this out, so you can help out the both of us! This is how I determine harvest!