Question: Does changing from HID to LED lights impact how often and/or how much you should be irrigating your plants? What advice can you give for adjusting to any setbacks? And are there any other factors affected by the change?
Answer: The decision to switch from high-intensity discharge lamps to light-emitting diodes has wide-ranging impacts across your cannabis cultivation operation, including on irrigation.
For starters, LED lights operate at lower temperatures than HIDs, reducing the heat load in your cultivation rooms by approximately 10°F. And because HIDs convert most of the energy into infrared light, leaf temperatures are also higher compared to those under LEDs.
These higher temperatures under HIDs increase the amount of water and nutrients plants take up through evapotranspiration, increasing the number of required irrigation and fertigation events needed. LED bulbs produce minimal infrared energy and only elevate leaf surface temperature approximately 2°F or 3°F higher than the ambient temperature. As such, irrigation can be reduced by up to 50% under LEDs.
However, setting proper leaf surface temperature targets is crucial for optimal plant growth, as it is where photosynthesis activity occurs. Maintaining proper leaf temperature also supports optimal plant enzyme activity.
Therefore, you must increase your heating capabilities for winter or in cooler temperatures when switching to LEDs and elevate your ambient temperature settings overall. With that, your air flow will need to be optimized to remove and control excessive heat and humidity, as well as encourage optimal enzyme activity.
The perfect conditions for a growing environment are dependent on multiple factors. Many growers using HIDs set the ambient temperature between 70°F and 75°F. Those utilizing LEDs often prefer temperatures between 80°F and 85°F.
When switching to LEDs, it is best to start at 80°F and adjust as required.
The No. 1 benefit to utilizing LEDs is electrical efficiency: Since the environment can operate at a slightly warmer ambient temperature, air conditioners run less often, saving electricity. (LED lights utilizing elevated temperatures may require enhanced dehumidification in some environments.)
Switching to LEDs will have major effects on how your plants grow, resulting in higher yields in most circumstances. Understand that changing light sources will require multiple adjustments, as there are refinements that will be required, especially when it comes to light spectrums.
The spectral output of an LED fixture will influence plant growth and secondary metabolites. For example, plants grown under LEDs with elevated far-red light typically tend to stretch out, producing longer stems and leaves, while elevated blue light levels encourage shorter, stockier growth patterns.
So, understanding the roles of light spectrum, intensity, and duration can help improve overall plant health, quality of the final product, bud structure, and chemical composition, such as the flavorant and aromatic qualities produced by terpenes, esters, thiols, and volatile sulfur compounds (VSCs). Some growers utilize specific light spectrums for specific cultivars to encourage a desired response, be it plant color or chemical production, or simply to enhance the bud structure.
When adopting LEDs, be ready to be flexible and make well-researched refinements to the environment. Be vigilant during your first growth cycle utilizing LEDs: Take the time to note crop differences and investigate any and all refinements required.
Kenneth Morrow is an award-winning grower and breeder. He is the owner of Trichome Technologies, a research and development company. He is also a consultant and author of the book "Marijuana Horticulture Fundamentals" and a founding advisory board member of Cannabis Business Times, where he has been a columnist since 2015. Find him on Instagram @trichometechnologies or reach him via email at: [email protected].
