I'm not sure of the temp or humidity. My lamp is about 10 inch of the plants, I'm using 1x 250w HPS with a fan running 24hrs, I've grown them from seeds & they're just over 3 weeks old, the problem seemed to start after I transplanted them! I put them in the same but new compost but with added perlite so I wasn't sure if was the stress of this? It seems to be the lower leaves that are affected the most so I dont think the light being to close was causing it!