I had the same problem just a few weeks ago. Its often a result of the leaves drying up because your humidity is too low in its living conditions. A lot of things that can cause this are like you mentioned the lights being too close, I keep mine at least 8" away but if your using 400-1000 watt sodium's, I imagine most people here are from what I read above than you obviously need a lot more room. Direct contact from any kind of fan is a big one. A lot of people will put fans right in front of their plants to promote stalk growth among other things but this can actually dry the leaves out. The best quick fix is to just raise the light a bit and change the airflow from directly on the plant to just in its direction. If its a full room you can move it back while still pointing it directly at them or if its in some kind of enclosed area try just turning it abit so it blows all around the plant. You'll still get the sway but without the "chapped" leaves in a sense. Hope this helps.