Hey I got my 25day old plants under my 400w hps a bit more than 2 feet away. Problem is its been gettin quite hot it even got up tp 31degrees celsius...Is this a problem? How far away should the light be?
A new 400w HPS bulb needs to be at least ten inches from all plant parts at all times to prevent light burn. It should be spaced about thirteen inches away to provide room for growth between adjustments, depending on how frequently it's adjusted. This doesn't take temperature into account but any 400w can use these distances with sufficient cooling. You may need more airflow through the lamp. Different exhaust and intake sources can also affect temperature.