What Color Light Is Best for Plant Growth?
For many outdoor gardeners, the winter marks the end of the planting season. Fortunately, you don’t have to suffer the same fate. By building a greenhouse or planting indoors, you can grow plants with different growing conditions all year round.
Before starting an indoor garden, one of the essentials you have to figure out is the kind of lighting your plants need. More specifically, you should know what color light is best for plant growth at different stages.
Make sure the light you pick has a good mix of red and blue diodes, which have the most effect on plant growth. If you plan to tackle everything from seed to flowering and fruiting to germination, look for full-spectrum LED lights.
Table of Contents
- Ultraviolet, PAR, Infrared Light’s Effect on Plants
- What Color Light Is Best for Plant Growth?
- Light Color Outputs By Source
- Color Light Best for Plant Growth
Ultraviolet, PAR, Infrared Light’s Effect on Plants
To know what color light is best for plant growth, we will have to dissect the spectrum of light. The light spectrum is only a tiny portion of the electromagnetic spectrum, which includes gamma rays, x-rays, microwaves, radio waves, and long radio waves.
Some studies have shown plants with diminished and improved growth responses to different electromagnetic waves other than light. However, for our purposes, we will only discuss the part of the spectrum containing ultraviolet rays, visible light, and infrared rays.
UV light is not visible to the naked human eye. In fact, it belongs outside the PAR range, and its variable wavelengths measure anywhere from 100 to 400 nanometers. Around 10 percent of direct sunlight is ultraviolet, which can be harmful to plants, just like in humans.
Ultraviolet rays fall into three categories: UVA measuring 315 to 400nm, UVB measuring 280 to 315nm, and UVC measuring 100 to 280nm. Shorter wavelength UV rays, such as the UVB and UVC, can be more harmful to plants. However, UV light applications in horticulture still require a lot of research.
In some cases, UV light exposure of plants results in darker coloring, improved coloration, and better taste, aroma, and nutritional value. Some studies show that UV exposure can alter the chemical compositions in plants and fruits, but to what extent is not yet clear.
The visible light spectrum is also called the photosynthetically active radiation (PAR), the light color range most suitable for different stages of plant growth. We can break it down into three subgroups: blue light, green light, and red light.
The part of the visible light spectrum with wavelengths 400 to 500nm is collectively the blue light spectrum. It is responsible for increasing plant quality by promoting stomatal opening and driving chlorophyll absorption for photosynthesis.
With a good amount of blue light, seedlings and juvenile plants in their vegetative stages can establish healthy stem and root systems. If you need plants to grow with shorter stems, blue light is also the key.
Next to blue light, the green light spectrum holds wavelengths from 500 to 600nm. Many scientists have written off the green light spectrum as less essential for plant growth. The reason behind these findings is that green light does not have as much ability as the blue or red spectrums to absorb chlorophyll readily.
Nevertheless, green light still permeates plants and gets absorbed through photosynthesis. As a matter of fact, the green light spectrum can penetrate deep below plant canopies, and only five to 10 percent of it reflects away. Generally, green light works pretty well with plants during most of the growth stages, given that it has a pairing of other colors.
Having a supplemental source of green light can be very beneficial for indoor plant growth. However, it can be useless if used alongside natural daylight or sunlight in greenhouses and outdoor plots.
Among the visible colors of light, the red light spectrum is the most effective for encouraging photosynthesis. These lights come in wavelengths between 600 and 700nm. Chlorophyll pigments absorb red light with much ease, resulting in general vegetative growth.
However, the stretching of leaves and flowers is a common effect. Overstretching includes deformed, elongated stems, leaves, and petals. You will need to balance red light with blue light if you want to avoid overstretching.
It is also vital to consider the efficacy of red light for plants kicks in better with a good mix of other PAR colors. Without a broad spectrum combination, red light alone presents the danger of burning delicate leaves and buds in younger plants.
Infrared Light (Far-Red)
Far-red light is the portion sitting within the range of infrared radiation. It has wavelengths between 700 and 850nm, and it does not belong to the colors visible to the human eyes.
Light on the far-red portion of the spectrum can affect the growth of plants in several ways. One way is by initiating a reaction of shade avoidance.
At deep red wavelengths of 660nm, plants will sense exposure to bright sunlight. However, as the wavelengths increase to 730nm and further, plants will feel the lack of light that looks like a shade or a canopy overhead.
As a result, excessive stem and leaf stretching will occur while the plant looks for red light sources. Nonetheless, the far-red light spectrum is also known for its usefulness in promoting flowering and increasing fruit yields.
What Color Light Is Best for Plant Growth?
The whole spectrum of light comes in portions that provide plants with plenty of benefits. These benefits vary depending on the growth stage a plant currently undergoes.
If you look at different sources, you will find that the life cycle of a plant subdivides into four to six stages. These stages include seed, germination, vegetation, budding, flowering, and harvest. Although the vegetative and flowering stages can be combined into the primary growth stage, you’ll soon find that both use different parts of the light spectrum.
The seed is somewhat a dormant stage in a plant’s life cycle. Although it contains all the nutrients it needs, nothing happens during the seed stage unless the seeds receive water, oxygen, and the proper temperature settings.
Before germination, the seed goes through processes called imbibition and respiration. The dry seed absorbs water during imbibition, rehydrates its cellular constituents, and swells with great force. The swelling ruptures the cotyledon and enables a primary root to come out.
As imbibition resumes the metabolic processes within the rehydrated seed, respiration occurs either using the energy from glycolysis or oxygen re-entry. When these requirements are met with the appropriate lighting conditions, the seeds jump onto the germination stage.
The lighting for seeds depends on the plant species you’re trying to grow. Some germinate in complete darkness, while others prefer continuous light. Where lighting becomes vital is after the seeds have sprouted.
The germination stage is where it gets tricky, as the right lighting conditions should be met before a seed can sprout. Science has categorized plants based on their seeds’ response to light concerning seed germination. The categories include positive photoblastic, negative photoblastic, and non-photoblastic.
Positive photoblastic seeds such as lettuce require light exposure to germinate. For these light-sensitive seeds, you’ll want to use red light to encourage germination. In contrast, far-red light has the opposite effect and may prevent the seeds from sprouting.
On the other hand, negative photoblastic seeds such as onion will not sprout with continuous exposure to sunlight. Non-photoblastic seeds will germinate regardless of light presence or absence.
Seedling or Vegetative Stage
During the vegetative stage, plants begin having tendrils and leaves, which means they will have a broader surface area for photosynthesis. In addition to light, plants in the vegetative state will need a nitrogen boost to grow more stems and foliage. In this stage, the plant transforms from being a juvenile into an adult.
Seedlings need a low-intensity, 24-hour combination of 30 percent blue and white and 15 percent red light. Then, increase the intensity once they’ve produced their first set of leaves.
Like seedlings, clones require low-intensity light to encourage root growth. At this point, you’ll want them to focus their energy to producing deep roots instead of growing upward. Hence, use a combination of 45 percent blue and white plus 25 percent red light.
After the seedling stage comes the vegetative stage. Here, the focus is still on root growth, so your best bet is to use blue light more than anything. Set your grow light at 100 percent blue and white light, while the red light should not exceed 60 percent.
Budding and Flowering Stages
When a plant becomes an adult, it will need extra phosphorus to transition into the blooming stage. For the development of healthy flowers and fruits, the essential ingredient plants need is potassium.
Light intensity influences flowering, stem length, leaf color, and plant food manufacturing during this stage. No matter how much nutrients you give your plants, they cannot process them to the full extent without adequate lighting.
Red light signals plants to start forming buds. However, too much of it can promote plant stretching and make the plants grow upwards too quickly. Instead of setting it at full blast, it would be best only to kick it up a notch from 60 to 80 percent, making sure to keep the blue and white light at 100 percent.
During the flowering stage is when your plants need all the photons it can get. Turn up the red light spectrum to 100 percent for the best yield and dense blooms. On the contrary, blue light will divert energy away from the buds and encourage the plants to grow more leaves instead, so you might want to dial it back a bit.
Ripening or Harvest Stage
Before the fruits mature and your crop is nearing its harvest, the plant no longer needs nutrients except for those it gets from light and water. A good balance of light lets you modify the type and rate of pigmentation in ripening fruits.
Light Color Outputs By Source
The amount of UV, blue, green, red, and far-red light varies from different light sources. As a rule of thumb, a good balance of blue and red is your best bet. Since white light contains a full spectrum, it can be your safest option.
However, your current planting conditions and budget restrictions will define the effective range of your light source. Each light source, natural or artificial, has a unique set of parameters that can qualify as pros or cons for each type of plant.
Generally speaking, sunlight provides the best food for plant growth. It offers the full range of plant-usable light, which even includes the non-visible UVA and far-red spectrum. Many plants thrive under the full blast of the sun’s rays, and they bring out more vibrant colors and lush foliage without malformations.
However, the sun also shoots gamma rays, x-rays, UVB, UVC, high-infrared radiation, and radio waves, all of which can be detrimental for many plant species. In many cases, you will have to transfer your plants under partial shading, or you might have to move them indoors.
While some plants enjoy feeding under direct sunlight, other plants like to flourish under the filtered light of the sun. In this condition, plants also receive the entire visible light spectrum, with harmful wavelengths toned down to manageable or negligible quantities.
When placed under direct sunlight for intolerable durations, such plants dry out or have their foliage burnt and damaged by the sun’s heat. Such occurrences should tell you to move your plants in areas that receive filtered sunlight.
Artificial Light Sources
Innovations in artificial lighting now provide gardeners with the option to propagate plants indoors. Even without a speck of natural light, plants can thrive as long as they receive a good mix of blue and red light in ample durations.
Of all the artificial light sources available, light-emitting diodes (LEDs) are the most popular. However, more traditional grow lights still grace the shelves of garden centers, including high-intensity discharge (HID) lamps and fluorescent lamps. In some budget indoor gardens, incandescent bulbs are still in use, but they consume so much electricity.
Among all the artificial light sources, LEDs produce the highest intensity of PAR. The trick to choosing this setup is choosing full spectrum LED growlights for indoor plants.
Each LED lamp has an array of diodes, and individual diodes could be carrying a different color of light. Good quality LED grow lights come with a combination of switchable or programmable light colors.
These features allow you to choose more blue-to-red light ratios for the vegetative stage of planting. Furthermore, you can switch to higher red-to-blue ratios when starting from seeds or pushing towards blooming and fruiting.
Advantages of LED grow lights vs HID lamps include a finely tuned spectrum, lower energy costs, and applications for all growth phases.
High-Intensity Discharge Lamps
If you are gunning for more specialized setups that focus on a particular growth stage of plants, HID lamps can provide you with several options. The most common types include metal halide (MH) lamps and high-pressure sodium (HPS) lamps.
MH lamps emit blue and violet lights similar to outdoor natural lighting conditions in springtime. As such, they work well for plants in their earlier developmental stages.
On the other hand, HPS lamps emit yellow and red visible light and small quantities of all different visible light wavelengths. With more energy from the red light spectrum, HPS lamps are perfect for germination, blooming, and fruiting.
For those on a tight budget, tube-style fluorescent lamps and compact fluorescent lamps (CFLs) should be enough for a starter garden. These lights provide better efficiency than the electricity-stealing incandescent bulbs, and they offer a much longer lifespan. Like LED grow lights, fluorescent lights also include a full range of visible light.
Color Light Best for Plant Growth
In summary, the best light color for plant growth depends on what growth stage a plant is in. For the germination of positive photoblastic and non-photoblastic plant seeds, give them a healthy dose of red light. As the young plants emerge, shift to blue light, and balance it with red during the blooming phase.
If you’re choosing full spectrum LED growlights for indoor plants, be sure that it has a good balance of blue and red diodes. Furthermore, pick a LED setup that provides enough coverage for all your plants. When choosing LED grow lights vs HID lamps, the former’s disadvantage is high initial costs.