Infrared Radiation Creates Leaf Temperature Gradients Down the Canopy
HPS bulbs emit a large infrared peak between 800nm and 900nm. This infrared peak significantly increases leaf temperatures at the top of the canopy, where most of the infrared light is absorbed. When examining the differences between leaf temperatures of plants grown in the same room under either HPS or LED lights, we will see significant temperature differences that infrared light causes.
In one of our studies, cannabis consultant Dr. Matt Wheatley measured the photosynthetic activity and internal leaf temperature of leaves at different distances from the light source. The internal leaf temperature measurements were very clear. The leaves of plants under LEDs did not show an increase for internal leaf temperature significantly above the ambient room temp at any distance between 2’ and 4’ from the lamp. In contrast, the leaves of plants under the HPS lamps showed a wide range of internal temperatures; the highest temps were apparent at the top of the canopy and lowest internal leaf temperatures were at the bottom of the canopy. This partially explains why HPS lamps produce top-heavy crops while LED lighting creates a more uniform canopy.
Since the rate of carbon fixation by RuBisCO is affected by leaf temperature and CO2 concentration, increasing the ambient temperature in LED-lit rooms will increase the rate of photosynthesis and plant growth.
Raise the Temperature in a LED Room
Based on scientific study and experimentation, Cannabis Consultant Dr. Matt Wheatley has found that an increase in the ambient room temperature of 5-7°C in LED-lit rooms relative to temperatures in HPS grow rooms is necessary to achieve similar internal leaf temperatures and plant growth rates as those experienced by plants in HPS-lit rooms. Keep in mind that as the ambient room temperature increases, the relative humidity decreases, and proportionate adjustments should be made to the relative humidity to adjust your Vapor Pressure Deficits.
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