New lighting technologies, such as CDL and LEDs generate light more efficiently, or with higher efficacy than incandescent lamps. In other words, we get more lumens per watt; however, heat per watt of electricity is constant. Fewer watts are used to produce equal brightness, not that CDL or LED light fixtures produce less heat for the wattage that they consume.
1 watt of electricity produces 3.412 British Thermal Unit (BTU) of heat per hour regardless of light type incandescent, HPS, CDL, LED, fluorescent, induction, etc. Therefore, a 1,000W HPS grow light (1,060W with ballast loss) generates 3,617 BTU per hour heat. A 500W LED grow light (550W with driver loss) generates approximately 1,877 BTU per hour heat. A 315W CDL grow light (335W with ballast loss) generates approximately 1,143 BTU per hour heat.
Physics of heat
British Thermal Unit (BTU) is the unit of heat energy. One BTU is the amount of heat needed to cool or heat one pound of water one degree Fahrenheit at a constant pressure of one atmosphere, equivalent to 251,997 calories.
The heat dissipated by an AC power operated electrical device is equal to the AC power dissipation per unit of time. Heat dissipation in BTU/hour is calculated by multiplying AC watt dissipation by 3.412:
1,000 W (1 kW) is equivalent to 3,412 BTU per hour.
1 kilowatt-hour (kWh) is equivalent to 3,412 BTU.