Quote Originally Posted by bigsby
Doesn't heat output depend on the efficiency of the light and the amounts of light produced at different wavelengths?
Quote Originally Posted by neceros
Well, different lights put out different heat. Some don't put any heat out at all, like LEDs. I believe induction lighting is also very very low. It depends on how the light is produced.
it's basic thermodynamics. if you're pumping 300w of electricity into a room, then 300w of energy has to come out of that room .. some way or another.

In a sealed room, it's going to be almost entirely heat, with a negligible % of it being chemical energy (i.e., the plants you grew).

The reason people say "LEDs are cooler!!" is not because a 300w LED makes less heat than a 300w HID. It's because you can grow nearly as well with 300w LED as you can 1000w HID. The reality is you're simply pumping in only 30% of the electricity, which results in only 30% of the heat.

(There is also the issue that many "300w" leds could actually be consuming only, perhaps, 250w of electricity... while 300w of HID could consume a real 300w in the bulb, plus maybe another 50w in the ballast... so suddenly your HID setup is in reality consuming 50% more electricity than a supposedly equal wattage LED).

That said: If you put 2 equal wattage lights, with equal ballast losses, in identical sealed rooms... they will both heat those rooms nearly exactly the same amount, no matter how efficient the lamp is. The brighter lamp room will simply cause the heat emanate more from the plants/walls than from the bulb.

Anyone who claims they have seen a significant temperature difference with the same wattage is either mis-measuring, or not using similar wattage.