Light technology: the effect of micromoles

During the winter season, there is not always enough light for maximum growth, so growers opt to use supplemental grow lighting. Light, when combined with CO2 from the air, provides food for plants. Plants ‘catch’ the light with their pigment chlorophyll and use it to convert carbon dioxide and water into sugar molecules (the building blocks for plant DNA material), along with substances such as nitrogen, potassium, phosphorus, calcium, magnesium and sulphur. The process that converts light into growth is photosynthesis. Without light, no plant growth is possible.

How much light is required based on the type of plant?
The amount of light that a plant needs differs significantly. The main determining factor is the type of crop. Plants out in the open need more light than plants that grow at the bottom of tropical rain forests. The amount of light needed also depends on other growth factors: namely, temperature and water. The rule of thumb is that for crops to perform to the best of their ability, they need a high level of light intensity.

Light particles determine photosynthesis
Plants do not distinguish between daylight and supplemental light. What matters primarily for photosynthesis is the number of light particles. Yellow, green and blue light provides more energy for plants than red light. Plants also obtain information from the air, for example about their position or about the right day length for blossoming. Special substances in plants – pigments – collect this information. Red light, for example, controls processes such as the growth and the flower formation of a plant. The colour of the light also determines the colour and size of the leaves. There is a difference of a factor of 1,000 between the much lower light intensity required for this controlling factor of light and the intensity required for photosynthesis!

More light means more growth
All plants take what they need from the air. More light also means more growth, but this curve has a diminishing incremental yield. The application of 50% more light can result in up to 50% more growth in the beginning, but this quickly reduces. This is because of the limiting effect of other factors, such as CO2, the temperature of the plant (and therefore the greenhouse) and the water management. Growers who use a higher intensity of light also have to adjust other growth factors: CO2 dosages, and a little more heat. By also properly controlling the other growth factors, growers can control plant growth using light. Controlling plant growth using light is mainly about quality, speed and quantity as long as you don’t have too much of any of these factors. To some extent, efforts to achieve greater quality affect the quantity, and vice versa.

Every crop reacts differently to light
Every crop reacts differently to the application of light. Crops such as Kalanchoe, Phalaenopsis and Bromelia can absorb CO2 only at night and can convert this into sugars only during the day in daylight. If the CO2 is depleted during the day, applying additional light has no further effect on growth. Plants that naturally receive little light – for example, at the bottom of tropical rain forests – also soon reach a point where further light makes no difference.