That plants need light to grow we all know. But this is a very simple and short explanation. What is their growth cycles really like in relation to the spectrum? In other words, which spectrum affects which stage in the growth cycles? Important questions to determine which LED lamp is needed or best suited to your crop, because the range on the LED market is huge.

Which characteristics of an LED lamp ultimately determine the yield/quality of your crop? It is too simple and not correct to only look at the lumen value. Lumen mainly says something about the amount of light the human eye can see. But plants (also) need other parts of the spectrum. This is indicated by the PAR (Photosynthetically Active Radiation) power. The PAR says something about the amount of light the plant uses for photosynthesis. The higher the PAR power, the more energy a plant uses from the light and converts it into nutrients to grow. The light wavelength of the PAR spectrum is roughly between 400nm and 720 nm. So it is important to look at a combination of factors to determine whether an LED lamp is suitable for your needs.

Light requirements by phase in the growth cycles

Plants use some colours within the PAR spectrum more than others, particularly wavelengths of blue light (400nm – 500nm) and red light (620nm – 700nm). But how do you know what the PAR density is with an LED lamp? You can see this back at the PPFD (Photosynthetic Photon Flux Density) value, written as µmol. Below are the values converted into requirements per phase in the growth cycles:

• 200-400 µmol: This is low intensity light. This light can be used well for seedlings and clones.
• 400-600 µmol: This is medium-strength light. This light is fine for early vegetables and cuttings.
• 600-1000 µmol: This is high-strength light. With this, you achieve the best development of growth and flowering.

Now that we know this, we can start looking at which colours belong to which phase.

Red and blue light

A plant mainly uses the blue and red light from the light spectrum. In this, the plant mainly needs  blue light to grow properly and strongly. This allows, among other things, the formation of  chlorophyll, the development of chloroplasts and the production of enzymes. The plant uses red  light during the flowering phase. This is why most LED lights are equipped with blue and red light,  as this stimulates photosynthesis. These lamps are also called Full-Cycle lamps. Red light,  balanced with the blue light, can be used throughout the entire growth cycles. From seed to  harvest. There are also full-cycle LED lamps where you can adjust the intensity of the red and blue  light. There is also, of course, the choice of using different lamps for different phases within the  growth cycles.

In addition, there are also LED lamps that, besides the main colours red and blue, also offer other  colours to offer as balanced a spectrum as possible similar to the sun, the well-known full-spectrum  lamps.

Ultraviolet (UV) light

We know UV radiation mainly from its effect on humans. We produce melanin to protect ourselves  from the sun’s rays which creates the well-known and popular tan skin. Plants, too, are naturally  exposed to UV radiation when growing in nature. In some cases, this also applies to flowers and  fruits and their colour can be enhanced by UV radiation. Farmers working at high altitudes claim  that their plants often produce more fruit. This is why many growers believe it is very useful to use  a little UV light. It is important to point out, however, that too much exposure to UV radiation is not  good. Damage to DNA, negative effect on photosynthesis and plant mutations can be a  consequence and harmful to humans.