Leaf Temperature vs. Ambient Room Temperature
The temperature of the plant takes precedence over ambient temperature. By employing a camera, you can regulate the climate based on your plants’ temperature. If the plant temperature becomes excessive, the OCL-master lighting controller reduces the lights to keep the stomata open. In the case of water shortage (e.g., pump failure), the lights might be dimmed or switched off to prevent crop damage.
When discussing photosynthesis and temperature, scientists commonly refer to leaf temperature rather than room temperature. This approach is logical because the biochemistry of photosynthesis occurs in the leaves of plants. In contrast, when grow room designers discuss temperature, they generally mean room temperature. In most growing environments, the leaf temperature surpasses the ambient temperature of the room, especially for plants cultivated under high-pressure sodium (HPS) lamps, which emit infrared radiation absorbed by the plants as heat.
VPD and System Temperature
Using an online calculator to compute VPD without accounting for crop temperature is erroneous. Relying on these levels without considering plant temperature is more likely to harm rather than benefit the plants. When using LEDs, the disparity between air and plant temperature is substantial, making it impossible to accurately calculate VPD without considering plant temperature. VPD values calculated without plant temperature are wholly unreliable and can lead to significant issues.
Plant Growth Temperature and LED
When cultivating with LEDs, the plant’s temperature becomes even more critical, as growers often apply their HPS growing methods and schedules to their LEDs. This approach frequently results in suboptimal growth due to the plant’s temperature not being at an ideal level. When cultivating with LEDs, temperature management is essential. This was already true during HPS cultivation, but it has become even more crucial with LEDs.
The reason why plant temperature holds such significance in LED cultivation is that unlike most HPS lights, LED lights do not emit infrared radiation. In HPS cultivation, infrared radiation contributes significantly to increased plant temperature, which has been associated with the ‘ideal’ temperature for many years. However, this approach is not entirely accurate. Plant temperature should always take precedence, as air temperature indirectly controls plant temperature. When cultivated with LEDs at the same temperature as HPS, the plants are generally too cold for the RuBisCo enzyme to function effectively, resulting in low enzyme activity and limited CO2 assimilation.
Plant temperature is also influenced by the LED lighting spectrum, intensity, and VPD. For instance, green light warms plants more than other colors. Therefore, specifying an ideal temperature is not feasible. A baseline can serve as a reference, which can be adjusted based on crop temperature until the optimal crop temperature is achieved.
Temperature Required for Photosynthesis
RuBisCo, a plant enzyme responsible for the initial step in carbon fixation, is temperature-dependent. Under sufficient sunlight, an ambient CO2 concentration of approximately 300 ppm, and a temperature range of 5°C to 27°C, the rate of CO2 absorption by plants and its conversion to sucrose increases with rising temperature, leading to a net increase in photosynthesis.
When the internal temperature of the leaf exceeds 27°C, the RuBisCo enzyme triggers the reverse reaction, converting sucrose and oxygen into CO2 and water. This process is known as photorespiration. As leaf temperatures approach 40°C, plants consume more carbon than they absorb, resulting in a negative net photosynthesis. Therefore, under normal ambient CO2 levels, growers can achieve optimal growth at lower leaf temperatures of approximately 25-26°C.
Fortunately, indoor growers can adjust their environment to create optimal growing conditions. A controlled environment enables growers to maintain the ideal temperature, carbon dioxide levels, light levels, and relative humidity. Let’s delve into how growers can adjust their growing conditions to take advantage of the heightened growth rates that occur at elevated temperatures.
How to Measure Plant Temperature
To obtain a reliable average temperature, plant temperatures should be measured across a broad leaf area.
The area of the plant that requires measurement is the part that receives the most light from the assimilation lighting. Positioning the crop temperature camera at the same angle as the assimilation lighting yields the most accurate readings, as photosynthesis primarily occurs where the most light is absorbed.
For the OCL SKWID1900 LED with a sapphire glass 120° lens, the camera should be oriented to capture as much foliage as possible and as little of other elements such as soil. The camera’s sensor has a wide beam angle, corresponding to a 1m diameter imaging area at a distance of 1m.
Distinguishing Plant Temperature Cameras from Infrared Thermometers
Unlike infrared thermometers, plant temperature cameras measure temperature across a wide field of view with plant-adapted emissivity, ensuring the most accurate measurements.
Infrared thermometers measure temperature with the smallest possible spot diameter, allowing them to measure only the temperature of a single leaf rather than the entire plant or multiple plants. Taking measurements from a distance can result in inaccurate readings from the lower layers of the leaf, where little to no light reaches. The emissivity of this type of meter is calibrated for building materials, not plants, necessitating the conversion of results for accurate measurement.
Plant temperature cameras provide continuous monitoring rather than snapshots.
12VDC ± 10%
RS485 digital bus
Temperature detection range
0 ºC – 60 ºC