If it isn't so hot, then the plants ( even seedlings ) can stay under a 400w HPS, maybe your seedlings just want to die. I have seen many growers using 600w HPS on a different site from start to finish with the light close to the plants and everything went great. They just had some really good air hoods that kept the plants safe from the heat. mrberrys, try not to let the soil get so dry. Water them regularly but Keep the top soil alittle wet. I think it should help. Good Luck on your grow :thumbsup: ...