Best Light Quality for your Greenhouse


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Does maximum light = maximum growth?

Light can impact yield, cosmetic appeal, fragrance, taste and potency; it is one of the most important ingredients for creating the perfect environment. If you can figure out what quality, quantity and intensity of light you need for your plants to grow efficiently, it’s going to determine how you design your greenhouse (GH). 

Structure and environment are the two primary factors affecting light level and quality inside of the GH.

Structural factors include glazing, structural components and equipment in or on the GH. Environmental factors include site location, time of day, season, air quality, and weather. The glazing determines what quality of light enters the GH while the structural components/equipment may obstruct light. Environmental factors play a much larger role in the quality of light that enters your GH, but these are also much harder, if not impossible for the grower to control.

What type of light do your plants need? 

There are different qualities of light, some are healthy, some can cause damage, and some don’t do anything at all for plant growth. When we are talking about light and its relationship to Photosynthesis we are really discussing the energy content of wavelengths. We have different qualities of light because only certain wavelengths can be efficiently absorbed by plants.

Plants love wavelengths within the 400 to 700 nanometer (nm) range. This is considered the Photosynthetically Active Radiation (PAR) range of light. PAR light is the light that is most efficiently absorbed by the plants for photosynthesis. In other words, if your plants are sitting in direct sunlight, the plant will primarily absorb and convert to plant food the light that is within the PAR range. To the human eye, PAR light is seen in different colors at different nms, and each color (wavelength) has a unique impact on the plant.

PAR Graphlight spectrum

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What is the optimum color for plant growth?

This depends on the grower’s priorities. PAR light promotes plant growth, and the different nms promote different plant characteristics in different growth stages, so there’s really not one perfect color for the plant. This is one of the reasons why sunlight is beneficial, because you get a range of different light qualities throughout the day. This is also what makes LED’s so appealing at different growth stages, because you can control the type, intensity and amount of the light that you deliver to your plants.

Brief summary of light color and its effect on plants:

Ultraviolet light (10 nm-400 nm):

Overexposure to UV light is dangerous for plants, however, small amounts of near-UV light can have beneficial effects. If used sparingly, UV light just below the 400 nm range can induce some stress on your crop which can have a positive effect on the plant’s colors, tastes and aromas with no noticeable effect on growth.

Blue light (430 nm-450 nm):

These wavelengths encourage vegetative growth. This type of light is essential for seedlings and young plants during the vegetative stage of their growth cycle. This light can reduce “stretching” in the young plants promoting a more stockier plant. It also stimulates the production of secondary pigments which can enhance colors and aroma. Too much of this light can stunt plant growth.

Green light (500 nm-550 nm):

Most green light is reflected by the plant and plays a much smaller role in plant growth than other colors. There are some important aspects of light in this range so a certain amount of this light is beneficial. For example, green light informs the plant of unfavorable lighting conditions so the plant can change accordingly. It also passes through plant tissue more efficiently than red or blue light which makes it more important for plants grown in dense shade.

Red light (640 nm-680 nm):

Red light impacts flowering and fruiting regulation. These wavelengths encourage stem growth, flowering and fruit production. The 660 nm wavelength has a very strong photosynthetic action, effective for inducing flowering of long-day plants or to prevent flowering of short-day plants.

Far red (730 nm):

Although the 730 nm wavelength is outside the PAR range, it can be used at the end of each light cycle to promote flowering in short-day plants such as Cannabis.

Overall, not all light is the same and not all light is efficiently absorbed by plants. On some level, more light is better, however, there are many other factors that can impact the outcome (temperatures, humidity, Co2, etc…). Plant’s benefit the most from light in the PAR range, but how much of that light do you really need for efficient plant growth, and how much is too much? In my next post we will talk about light quantity.

Do you have any experience with this topic? Have any suggestions? Can you elaborate on different colors and their effect on plant growth/health? Please leave you thoughts in the comment section below.

-Disclaimer: If you are considering adjusting your lighting, please do further research on this topic because different types of light can have a negative impact on your crop.


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