LED grow lights are increasingly popular for indoor horticulture, leading many growers to question how these modern fixtures manage their thermal output. The simple answer is yes, LED grow lights produce heat, just like any electrical device that converts energy. However, the heat production from Light Emitting Diode (LED) fixtures differs significantly from older lighting technologies, such as High-Intensity Discharge (HID) lamps. This difference is a fundamental change in how heat is generated and distributed. Understanding this distinction is necessary for maintaining the precise environmental controls required for optimal plant development.
Understanding LED Energy Conversion
LED grow lights are considered highly efficient because they convert a much larger percentage of electrical input into Photosynthetically Active Radiation (PAR) light compared to older bulb types. While traditional HID lights convert approximately 70% to 80% of their energy into heat, modern LEDs can convert a greater portion, sometimes 40% to 50%, into usable light. The remaining electrical energy is then dissipated as heat.
This waste heat is generated primarily at two specific locations within the fixture. The most significant source is the semiconductor junction, the tiny diode where the electrical energy conversion takes place. The second major source is the LED driver, the power supply component responsible for converting the incoming Alternating Current (AC) power into the Direct Current (DC) required by the diodes.
Impact of LED Heat on the Grow Space
The heat produced by LED fixtures affects the grow room environment differently because it is largely convective rather than radiant. Convective heat warms the surrounding air, causing it to rise and increasing the ambient air temperature of the grow space. This contrasts with the intense infrared radiation from HID lamps, which directly heats the surface of the leaves.
This distinction is important because plant metabolism is driven by leaf surface temperature (LST), not just the ambient air temperature. Under HPS lights, the radiant heat raises the LST significantly above the air temperature, promoting processes like transpiration. Because LEDs produce far less radiant heat, the plant leaves remain cooler. Growers sometimes need to raise the ambient air temperature by 5 to 9 degrees Fahrenheit compared to an HID setup to achieve the same optimal LST.
If the LST is too low, the plant’s metabolic functions, including photosynthesis and nutrient uptake, can slow down. Growers must monitor LST closely, often using an infrared thermometer, to ensure the plants are operating within their ideal thermal range. Proper air circulation is necessary to prevent pockets of warm, stagnant air around the fixtures and to ensure a consistent thermal environment across the entire plant canopy.
Strategies for Managing LED Thermal Output
Effective thermal management is necessary to maintain both the performance of the LED fixture and the health of the plants. The efficiency and lifespan of the diodes are highly dependent on keeping the internal junction temperature low. Manufacturers address this by incorporating passive cooling components, most commonly heat sinks. These sinks are often made from thermally conductive materials like aluminum and are designed with fins or a chassis structure to maximize the surface area for heat to dissipate into the air. Some LED fixtures also utilize active cooling, such as integrated fans, to forcibly move air over the heat sink and accelerate the heat transfer process.
Another common strategy is to relocate the sensitive LED drivers outside of the grow area, which removes a significant heat source from the room and extends the driver’s lifespan. Since drivers are often the most common point of failure in LED systems, isolating them from the heat of the diodes and the high temperatures of the grow room is a practical solution.
Grow Room Management
From the grower’s perspective, managing the heat involves optimizing the grow room’s ventilation and exhaust systems. Exhaust fans remove the warmer, convective air generated by the fixtures, while intake fans draw in cooler, fresh air. Proper air circulation from oscillating fans helps prevent heat buildup directly around the light fixtures and ensures uniform temperature distribution across the canopy. Maintaining the correct distance between the light and the canopy also helps distribute the light’s thermal energy over a wider area, preventing potential heat stress.