In the world of plant lighting there is a war being waged between HID lighting and LED lighting proponents. Internet forums are the battlefields where opposing sides come together with anonymous names like “LEDGuru” or “LEDGuruIsLame”. Each side is stacked with lighting manufacturers and lighting distributors trying to prove the superiority of their system. The battles are being waged under the guise of the Average Joe who has tried everything but was so passionate about a particular brand that he or she decided to make a promotional video.
I suggest we end this useless animosity with an old-school wedding. To quote an old friend, “The success of a relationship does not depend on how much you have in common, but in how well your differences compliment each other.” It is these differences that make LED and HPS/MH a perfect match. Understanding the light requirements of plants is the first step in ending this unfortunate misunderstanding.
The Light Compensation Point is defined as the minimum amount of light required for the rate of photosynthesis to exactly match the rate of respiration. During periods of low light plants will use energy reserves until they are depleted and a sort of starvation occurs. The important thing is that the light intensity should exceed the light compensation point. The Light Saturation Point happens when photosynthesis is at a maximum, and increasing light will no longer increase the growth rate. Photosynthetic rates are proportional to light intensity only to a certain point. Exceeding the saturation point is pointless, and results in needlessly high electric bills.
When light energy greatly exceeds the saturation point, we run into Photoinhibition. There are two types of Photoinhibition: dynamic and chronic. Dynamic Photoinhibition is reversible, as plants are able to use natural defenses to divert the excess light energy. This ability is limited in many plants leaving them with little resistance to the effects of high light levels. Chronic Photoinhibition is caused by long-term exposure to light levels well beyond what plants need, causing irreversible damage and eventually death.
The amount of light a plant can use is dependent on the entire propagation system being optimized. Radiant heat (IR) is major factor in changes of Compensation Point, Saturation Point, and the point at which Photoinhibition begins. HPS/MH lighting provides excess IR, requiring exhaust fans to control temperature. In HPS/MH lamps 70%+ of the light output is emitted as IR (heat). With this inefficiency, garden size is limited, using only HPS/MH lights.
Well made LED grow lights solve the HPS/MH problem of too much heat. Using 5mm HBLEDs we are able to create compact arrays where over 99% of the light is readily absorbed by plants for photosynthesis and virtually no heat is emitted. LEDs provide an extremely rich plant light source (when the correct wavelengths are included). When gardeners replace HPS/MH with LED grow lights, due to the lack of radiant heat (IR) plants may not be able to process all of the light absorbed from the LEDs, and Photoinhibition becomes a concern.
When HPS/MH and LED are used in a Hybrid Method, together in the same indoor garden, we are able to bring out the best in the both of them. Turn the HIDs on for a few hours a day to heat up the plant canopy and let LEDs work the rest of the photoperiod. The result is 50-80% less money out of your pocket while conserving resources and maintaining your expectations. May HPS/MH and LEDs live happily ever after.
Angela Lundmark is an indoor gardener and freelance writer.
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