600w hps is much cooler than 400w hps in my experience. Iv ran both. 600w definetly has room much cooler. Hps in general ( what I read and experience ) are way cooler.
Do you have both? Test them. Put each in a tent for 1hr with no ventilation. There is no way 400 is hotter than 600 its basic math except maybe if the 400w is magnetic and the 600 is digital ballast.
Yeah but I always thought the mh bulbs had a bad rep for heat, even more so than hps, so your probably right I’m not really basing it on anything lol
1 watt gives 3.412 btu per hour, regardless if its amazon cheap led, fancy QB or even MH or HPS. But some lights gives more lumens per watt then others making them more or less efficient.