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from Kelly Usa

Led Grow Lights: The Science Behind These Popular Lights

Thinking of growing plants such as tomatoes indoors? You will almost certainly have been advised at some point to look into LED grow lights, as they are lower energy, last longer and require a lot less cooling of the grow as part of your set up. Ultimately using LED grow lights you will end up with a cheaper and better harvest than other systems in terms of $ per gram of vegetation. What’s the science behind these and why are they a better option than more traditional lighting systems? 


Photosynthesis – the magic of plant growth 

Plants use light to combine carbon dioxide (CO2) and water (H2O) to produce carbohydrates such as sucrose, cellulose and starch (collectively known as sugars). 

In order to do this, special pigments in plant cells get energised by light of certain wavelengths. There are two broad types of photosynthetic pigments, the chlorophylls and the carotenoids. Chlorophylls a, b, c, and d each absorb a set of light wavelengths, while carotenoids such as beta carotene use light to do different things, including controlling the growth cycles of the plant as it matures. 

Different pigments for different purposes 

When a pigment absorbs a light photon travelling at a certain wavelength it gets excited and begins a chemical reaction that will do certain things to the plant. Chlorophyll a uses the light to create sugars and thereby helps the plant grow. Beta carotene absorbs a slightly different wavelength and is used to control when the plant grows and when it rests.   

Between the different pigments the plant achieves different functions. The light that it doesn’t use is reflected back, and since most plants don’t use the green wavelengths we see them as green as that light is reflected into our eyes. 

The most used light wavelengths sit at the blue and red ends of the light spectrum. Over the years, scientists have experimented to see just what lights do what job and have tried to refine it down to providing just a few wavelengths so they can grow plants indoors. NASA for instance are trying to grow crops indoors for long distance space missions. 

Different lights used over time 

Over the years some of the best lights used for indoor grows have been metal halide lamps. These produce an intense white light but also produce a lot of heat and use a lot of energy. The great leap in LED grow lights has been that it is possible to send exactly the light wavelengths to the plant without using so much energy or wasting that energy as heat. 

LED grow lamps will use 7-10 wavelengths of light to trigger photosynthesis in the plant. These might include ultraviolet (UV) at 410nm, infrared (IR) at the opposite end of the spectrum  (730nm) and a range of lights between. Tomato plants in particular likes infrared and ultraviolet as well as many of the visible light wavelengths to grow effectively. 

Each LED chip will have a colored emitter that ensures only a specific light will be emitted on something called a Chip On Board system. Each chip will have a small parabolic reflector that focuses the beam of light and keeps it separate from the next chip. Above the LED as a whole there will be a 90 degree lens that focuses the combined beam on the vegetation. 

While we may see the light as a pink hue the plants will see exactly the full spectrum of the light that they need and their photosynthetic processes will act accordingly, with lush, strong growth appearing throughout its lifecycle. 

By providing exactly the right wavelengths and using a lot less energy so LED grow lights are a far more efficient and effective light for indoor growing. Lasting up to 60,000 hours you will find that they will help you produce vegetation for up to five years so the higher initial investment than metal halide will generate much better savings in the long term.