The Forgotten Spectrum and Importance of Green Light for Crop Quality

August 6, 2015

The Role of Green Light in Photosynthesis

It is clear that green light is a player in photosynthesis along with the other portions of the spectrum. How and where does this occur? Green light is transmitted through a plant’s organs and is utilized in deeper layers of cells. It is also used in the intra-canopy leaves and is more efficient than either blue or red light at driving CO2 fixation at the abaxial (lower) sides. In fact, the photosynthetic efficiency or quantum yield for green light is similar to that of red light, and greater than that of blue light in the deeper layers of a leaf. Plants grown under a full spectrum tend to have thicker leaves, higher net photosynthesis and lower senescence (i.e. biological aging). On the other hand, green light also stimulates shade responses in plants so the amount of green delivered has to be carefully balanced.

White light as a replacement for green LEDs

Green light has proven important for the overall health of a plant. As the electric efficiency of green LEDs is comparatively lower than the efficiency of diodes of other LED colors, green light can be provided as a part of a spectrum emitted by more efficient white LEDs. The main difference, apart from the cost, is the level of control in the spectral quality of a light output. Research conducted in-house at our research center in Sweden to test the difference in spectral quality between the use of green and white LEDs has shown that white LEDs emit enough green light and can be used as an efficient source of green wavebands for LED grow lights without any negative effect on plant growth and development. It also has shown a significantly lower energy consumption compared to using pure green (530nm) diodes. At Heliospectra we recommend horticultural lights containing green LEDs for applications where a high level of spectral control is prioritized or needed for a certain experiment. But for commercial growers, prioritizing energy efficiency and using white (5700 K) light LEDs is sufficient for great plant health and making sure the energy costs stay low.

The bonus - a more pleasant light to work in

There are also other benefits of using white diodes in an LED grow light. As many LED companies produce fixtures containing only red and blue light, they emit an intense pink light. This can be very hard on the eyes, creating an unpleasant work environment and difficulties for diagnosing plant health. By using white LEDs, a more pleasant light is emitted, which is better for workers and allows growers to see the shifts in crop quality.