As growers are educating themselves more on different lighting technologies, we have been faced with questions many times over about what effects different light sources have on temperature and crop production; what is the difference between Convection Heat and Radiant Heat?
Anyone remotely familiar with HPS (high pressure sodium) and LED lighting understands that you need to maintain a certain distance from your crop to the hot HPS luminaires, while cooler LEDs can be mounted closer to the canopy. Both of these lighting applications have their pros and cons depending on the crop you are growing.
We also know that using LEDs can save an indoor grow in cooling costs while HPS lamps can save a growing operation in heating costs (especially for those in Northern climates). However, there is a common misconception when calculating efficiencies. When we calculate the load for heating/cooling equipment we use a measurement of energy called British Thermal Units (BTUs). A BTU is equal to the amount of energy used to raise the temperature of one pound of water one-degree Fahrenheit. When factoring in the heat given off by a luminaire, the BTUs are calculated off of the total wattage of the luminaire. If you have a 600 Watt HPS lamp, the BTUs for that luminaire are the same as a 600 Watt LED. A single watt of power is equal to 3.41 BTUs so a 600W luminaire will produce 2,046 BTUs. This is true for both the LED and the HPS luminaires.