Menu
LED grow lights play a vital role in the success of an indoor grow facility. While measuring ambient room temperature is important, it doesn’t fully reveal plant vitality. This is why tracking leaf surface temperature (LST) is so beneficial. LST provides growers with valuable insights into how plants respond to their environment. By monitoring LST, growers can make precise adjustments to optimize conditions, ensuring the highest and healthiest yields.
It must be noted that leaf surface temperature is not the same as ambient air temperature. Air temperature affects LST in the grow room, but it is not the only factor that affects LST.
A too-warm room temperature stresses plants out, while too-cold temperatures halt growth. For maximum yields, it is important to find the perfect ambient temperature. There are also different optimal LST ranges that maximize growth of secondary metabolites such as cannabinoids, terpenoids, sterols, flavonoids, and others—so it is important to consider the purpose of your cultivation when measuring LST.
What Affects Leaf Surface Temperature
Yield-optimizing LED grow light systems have been proven to benefit ambient air temperature in grow houses.
The metabolic reactions that keep a plant alive each operate at a different optimal temperature range. Photosynthesis is the most important of these metabolic systems, as it is vital to the plant’s survival. Optimal temperature ranges depend on which process needs to be enhanced.
For example, ideal temperature is subject to:
In general, growers should adhere to these guidelines:
LST depends on the plant species/variant and concentration of CO2. And in any given grow room, trial-and-error can help determine the ideal range for LST.
A more in-depth look at the factors affecting LST:
Air temperature sets the foundation for leaf temperature, warming the leaves that are cooler than the air, and cooling leaves warmer than the air.
Leaves typically cool themselves by evaporating water through stomata (a process called transpiration)—much like sweat flows through pores to cool the body. The efficacy of transpiration is determined by the vapor pressure deficit (VPD) , which refers to the relationship between the relative humidity in the ambient air to the relative humidity in the leaf. Higher relative humidity typically increases leaf surface temperature by reducing this evaporative cooling. The spectrum of light the leaf is receiving also affects leaf surface temperature.
According to extensive research, chlorophyll, the primary driver of photosynthesis, most efficiently uses blue and red light. This does not mean that green or yellow light is unusable, it means that plants use that spectrum of colors less efficiently. Optimizing the light spectrum, by utilizing light that emits a high volume of blues and reds, will increase photosynthesis while also keeping the leaves at a cooler temperature.
A less efficient spectrum will tend to heat the leaf more, while a more efficient spectrum keeps the leaf cooler—because more light energy is being converted to plant-usable energy instead of heat.
Light spectrums optimized for plants will therefore require a warmer ambient air temperature to keep the LST in the ideal range than spectrums not optimized for plants. Since heat management is generally a concern in indoor gardens using artificial light, these higher ambient temperatures can result in significant savings.
There are many tools (probes, IR thermometers) that give an accurate reading of leaf surface temperature at a single point.
Issue? Temperature can vary dramatically across the leaf, depending on which areas of the leaf are fully exposed to light or covered in the shadows.
Solution: A forward-looking infrared camera (FLIR) provides a more accurate depiction of leaf surface temperature and light efficiency.
Note to Grower: Measure the top, middle, AND bottom of the plant. This will give you a complete survey of the conditions of your crops, which will tell you where you need to make changes.
The different types of grow light fixtures create different light spectrums. LED grow lights differ significantly from other forms of electric grow lights because the spectrum of the light can optimize certain wavelengths, or colors, over other colors—enhancing plant-usable light.
In comparison, other light sources produce much of their light as an unintended byproduct of their operation system, producing wasted energy and heating up plants. LED grow lights without optimized spectrums will also produce wasted energy while heating up plants.
In certain cases, an LED yield-optimizing spectrum can require ambient temperatures of up to 10 degrees warmer to keep the LST at the ideal range for a maximized yield.
High pressure sodium (HPS) grow lights convert a large portion of energy consumed to non-visible infrared (IR) light in the 810-830 nm range. This IR light can be perceived by humans (and plants), because of the warmth it creates, but it does not have enough energy to fuel photosynthesis.
Additionally, HPS lights produce primarily yellow light, which is the intermediate in terms of energy between blue and red light.
When growing under LED lights with a red- and blue-dominant plant-optimized spectrum, the lack of excess infrared and other directly usable light causes the leaves to remain cooler, meaning that ambient air temperature needs to be significantly warmer than for the same plant grown under any light (natural or electric) which is not optimized for plant growth.
LED lights with a high concentration of “white” LEDs produce mainly green and yellow light. This range warms up the leaves more than reds and blues, but because the white light lacks the 800+ nm infrared output of most HID lights, the ambient air temperature may still need to be slightly warmer to get the ideal LST.
If you are switching from HID to LED, you will need to amp up the room temperature slightly with white LEDs, but much higher if you are using a plant-optimized spectrum grow light. If you don’t adjust the room temperature according to the spectrum change, your plant growth will be limited.
Again, when using optimized-spectrum LED grow lights, ambient air temperature MUST be kept higher in comparison to other lighting types, to achieve the same metabolic rate.
It also must be noted that when testing LED lights against other types of lights, such as HPS, the leaf surface temperature should be kept consistent under each light—to enable identical metabolic rates—ambient air temperature aside. This is because with plants grown under MH and HPS lights, the leaf surface temperature differs enormously.
Running a warmer indoor growhouse, as required for spectrum-optimized LED grow lights, can lead to significant reduction in costs associated with cooling systems, such as ventilation or air conditioning.
Reduced Need for CO2 Supplementation
When using spectrum-optimized LED grow lights, the reduced need for cooling also reduces the need for CO2 supplementation. This is in comparison to a growroom needing a cooling system, such as ventilation, which results in the loss of CO2.
LED technology allows complete control over the light spectrum, which means cooler leaves for your plants at the same ambient temperature.
Using spectrally optimized LED grow lights simplifies the process of achieving the ideal leaf surface temperature, making it both easier and more cost-effective. This optimization leads to higher yields and greater returns on investment, as plants thrive under the most favorable conditions. By ensuring optimal light conditions, growers can maximize their productivity and profitability.
Grow Pros Solutions is the NOW for Horticultural Science & Engineering. Grow Pros Solutions is one of the leading manufacturers of high-performance LED grow lights designed for cannabis cultivation. Our focus is to create top performing lighting solutions and fixtures that enable previously unobtainable and unthinkable results, increasing productivity from 30-60%. Our unwavering commitment to advancing technology and finding more efficient and sustainable solutions has made us a gamechanger for thousands of commercial and home growers.
Enter your email here to confirm your interest