[cannabis54321]

Iv had 4 plants under a 400 watt hps for 2 weeks now for the flowering stage, I have the light 9 inches above the tops of the plants, and the tops of the plants are turning white, is this because the light is too close? How high above my plants should the light be? If the leaves are burnt should I cut them of or should I just let the plant heal itself? Please respond, I need to know before I ruin my harvest, iv put to much time and money in to this.