Fundamentals

If you have been researching LED grow lights for your plant growth facility, you have likely been ending up with a variety of information that lighting manufacturers use to market their products: watts, lumens, LUX, PAR, PPF, PPFD. In our opinion, you want to buy a lighting system that delivers the required amount of light to your plants. In order to explain the correct method for evaluating a horticulture lighting system, it may be a good start to focus upon what you need to avoid.

First, the watt of the LED’s is not relevant. The wattage of the LED use in light does not tell you anything meaningful about the lighting system’s performance since LED and fixture efficiency varies widely. Remember, the LED wattage is a system input, and growers care about the system output–PAR Output. Hence, the lighting system using a certain wattage needs to be compared to the watt it is consuming to produce PAR.

Second, do not look only at one PPFD measure. Unless you are growing a small plant directly under your light, a single PPFD measurement does not tell you much. By clustering the LEDs closely together and using narrow beam optics, it is very easy for a manufacturer to show an extremely high PAR measurement directly under the fixture. However, unless you are only growing one plant in this exact location, you need to know how much PAR is being distributed across the entire canopy.

Therefore, we believe the industry acknowledges that at least these are relevant questions to be answered when researching LED grow lights:

How much instantaneous PAR from the fixture is available to plants (measured as PPFD)?

How much PAR is being distributed across the entire canopy?

How much wattage is used by the fixture to make PAR available to your plants?

Although we like to deliver lights, we also encourage a broader assessment about how much lighting is needed and how to optimize your investment. Think about that different amount of light is needed over the growth cycle and depending upon other aspects such as DLI. Also consider that in complexes such as greenhouses, the efficacy of the lights may be sensitive to temperature.

The exact spectrum used has some importance. Individual farmers may have different light strategies, but there are no longer so much secrets in those. We are happy to support such experimentation, but the below can be used as guidelines.

The light that plants predominately use for photosynthesis ranges from 400–700 nm. This range is referred to as Photosynthetically Active Radiation (PAR) and includes red, blue and green wavebands. Blue and red light is mostly focused upon because their linkage to chlorophyll. Chlorophyll most strongly absorbs red light (600–700 nm) and blue (400–500 nm) and some green light (500–600 nm).When combined with other light wavebands, blue light enhances plant compactness, rooting, and the production of metabolites. Blue light is a growth regulator, which can reduce your need for chemical plant growth regulators. Blue light can also increase chlorophyll accumulation and stomatal opening, which improve overall plant health.

Since chlorophyll does not absorb green light so much, many have thought green being less important. This lower chlorophyll absorption rate, compared to blue and red light, is what makes most plants appear green. Depending on the plant, leaves generally reflect 10-50% of green waveband photons.

In contrast to these beliefs, studies of green light in plant growth have concluded that green light is important to photosynthesis, and especially in a plant’s lower leaves. Around 80% of green light transmits through chloroplasts, whereas leaves absorb approximately 90% and transmit less than 1% of red and blue light.

This means when there is a lot of light, chlorophyll reaches a saturation point and can no longer absorb red and blue light. Yet, green light can still excite electrons within chlorophyll molecules located deep within a leaf, or within chloroplasts lower in the plant’s canopy. Moreover, green light enhances photosynthetic efficiency—increasing crop yields, during bright light conditions. A lot of scientific studies has proven this to be the case. However, please notice that farming in greenhouses means some green is provided, and the level needed is lower.

Red light is among the best for stimulating photosynthesis and promoting plant growth. Although high levels are needed, plants grown under only red light tend to become stretched. Therefore, adding blue light and other spectrum balance out and result in more compact plants with thicker leaves. Certain plants need more balancing than others, but a few spectrums can be used for all crops.

Please also notice that the UV waveband is outside of the PAR waveband contains new applications. Color can change in certain wavelengths and studies show UVB can increase essential oil content and phenolic compounds in certain crops. UVC does also influence plant resistance. Alternative light solutions can help to boost such processes.