Everything You Need to Know About Grow Light Spectrum

Typical Use of the Grow Light Spectrum

Did you ever try using a grow light system to help your indoor plants grow? If yes, then you’re most likely in awe at how plants use up the energy from the lights to make themselves flourish healthily. But do you wonder exactly what is it in these lights that make your plants grow and develop well?

One of the most important factors to look out for when creating or purchasing a grow light system is the color spectrum. The successful growth, development, blooming, and fruiting of a plant highly depends on the correct color of light used on it. Fancy grow light systems and light bulbs will be of no use if they are not in the right color spectrum because your plants will not get the proper nourishment they need.

You need to have a basic grasp of a few concepts on light spectrums to be able to fully understand how it works on plants. Hence, this section will discuss the typical use of the grow light spectrum and will also include an explanation of the color spectrum, spectral types, the mechanism by which sunlight is used by plants to generate food, and the general color spectrum range of common grow light lamp systems.

What is a Light Spectrum?

If you were to hold a prism in between a white sheet of paper and a light source, what would you see? The reflected light from the source looks white to your naked eyes. But when the light passes through the prism, you’ll see that the beam will reflect all the colors of the rainbow.

The prism earlier used serves as a medium to spread light out via its wavelengths, forming a spectrum on the paper sheet. The spectrum starts with the lowest wavelength color, violet, located at the far-left side. It gradually lightens across the spectrum as wavelengths increase until it reaches the end on the far-right side. This is where the highest spectrum color, deep red, is located.

The Three Light Spectrum Types

The light from stars such as the sun, as well as those from artificial lighting sources, can be analyzed by classifying them into corresponding light spectrum types. These include continuous spectrum, emission spectrum, and absorption spectrum.

Continuous spectrum

A continuous spectrum is one that has all the colors of the rainbow appear flowing continuously without breaks in it. The spectrum created by holding a prism in between a light beam and a blank white paper sheet is a good visible example of a continuous spectrum.

Light waves emitted by stars, such as the sun, produces a continuous spectrum. Heated solid opaque objects, like incandescent light bulb’s filaments, also emit this kind of spectrum. Hot dense gases in space also produce this spectrum.

Emission Spectrum

Transparent gases that give off light will produce a spectrum that looks like rainbow lines placed side-be-side against a black background. This is called the emission spectrum.

The rainbow lines you’ll see appear at particular wavelengths and come from the quantum nature of atoms. The lines are properly termed emission lines.

Emission spectrums are not limited to hot transparent gases in space. The spectrum is also formed by neon lights, some fluorescent light types, and typical streetlights.


Absorption Spectrum

Think of the absorption spectrum as the visual opposite of the emission spectrum. The absorption spectrum looks like a continuous rainbow spectrum with dark lines at specific wavelengths. The spectrum can be a product of light waves passing through cool transparent gases.

The dark lines on this spectrum are a result of gas atoms that absorbed specific light wavelengths, hence the name absorption spectrum.

The Color Spectrum

Light is radiation in the form of electromagnetic waves. These waves have varying polarizations, intensities, and wavelengths. Electromagnetic radiation from light can be placed in a spectrum to describe their respective attributes.The spectrum also includes the light colors that are visible to the human eye, namely:

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet

These spectral colors are popularly known through the mnemonic “Roy G. Biv”.

Among these seven colors, two are considered most important for plants. They are red and blue. Plants readily absorb red and blue colors from light, and that’s the reason why leaves don’t appear in reddish and bluish hues.

The colors in the spectrum have corresponding wavelengths that determine their respective energy content. Wavelength is expressed in nanometers (nm). As the wavelength of light increases in the spectrum, its energy content decreases.

Plants need to be exposed to certain ranges of wavelengths, and thus to certain colors of lights, to grow, thrive, and bloom properly(1).

Blue lights are in the low end of the spectrum, carrying a wavelength range of 400-500 nm. This means that these lights are high-energy ones that can be used to jumpstart the growth of seedlings and small plants.

Red and far-red lights lie at the high end of the spectrum. Red lights have wavelengths of 600-700 nm, while far-red lights have wavelengths of 700-800 nm. These lights emit lower energy and are usually used for the continuous development of plants.

How Sunlight Affects Plants

Light from the sun is a key ingredient that plants need for manufacturing their food through photosynthesis. Plants utilize sunlight together with carbon dioxide and water for photosynthesis to happen(2).

The sun carries a full spectrum of electromagnetic radiation. This means it can emit the entire color spectrum, from blue to red, as it shines over the Earth.

Light waves emitted by the sun pass through the Earth’s atmosphere and reach plants. Note that not all light waves on the color spectrum get absorbed by plants. It’s only red, blue, and green waves that are significantly absorbed by plants.

Chlorophyll, a green pigment in plants, catches these light waves and absorbs the red and blue ones. The plants then turn these waves into chemical energy and store them to be used with water and carbon dioxide later in manufacturing their food(3).

Chemical energy from the sunlight will then combine with carbon dioxide and water to form a sugar called glucose. Glucose is the primary sugar needed by plants to create energy for all plant processes needed to grow, thrive, bloom, and fruit.

Glucose is also a key ingredient in manufacturing two other vital substances to plants: starch and cellulose. Starch is a carbohydrate used by plants as another source of food(4). It is primarily stored in seeds, stems, and other parts of the plant. Cellulose is a compound substance that is a vital structural component in creating plant walls(5).

Greenlight waves from the sun also get absorbed by chlorophyll. However, they are not turned into energy as do red and blue waves. The green waves are reflected off leaves and stem instead, giving most plants its characteristic green color. This is why chlorophyll levels in a plant can affect their color.

Typical Uses of Color Spectrum

The electromagnetic color spectrum has various uses in different fields.


Visible colors in the electromagnetic spectrum enable humans to communicate with each other easily. For instance, different colors are used in traffic signs and warning signs. Red traffic lights signify stop, yellow warning signs on hospital waste bins mean infectious waste, and so on.


In psychology, all the colors included in the spectrum have various meanings. They are used to symbolize feelings and physical attributes. For example, blue connotes calmness and serenity, violet is associated with luxury and royalty, and green means balance and harmony. Visible spectrum color can also help alleviate anxiety and improve moods (6).


Colors have been used since ancient times to treat illnesses. In this modern time, chromotherapy (color therapy) uses the visible color spectrum to help balance certain energies that are lacking in a sick person’s body(7).

Electromagnetic waves from light are also used in light therapies designed to treat a newborn baby’s jaundice or yellowing of the skin(8). Lights that emit UV rays are placed underneath a jaundiced baby to help remove the substance that causes the yellow discoloration of the skin.


In gardening, the color spectrum is useful for determining the lights that will be used in a grow light system. Determining the wavelengths and color temperature of the different colors in the spectrum is key to knowing which lights plants will most likely be responsive to growth and blooming.

Color Temperature Range of Grow Light Lamps

Light waves emitted by all light sources, be it natural sunlight or artificial lamps, have their corresponding color temperature. This refers to the relative warmth or coolness of the light. Color temperature is measured in Kelvins (K).

Lights on the lower end of the color spectrum have temperature readings of 1000-3000K. They produce reddish light and are dubbed warm lights.

On the other hand, lights on the upper end of the spectrum have 5000-6500K temperature readings and produce clear white light. Lights with temperatures of 7000-10000K produce bright bluish light. All these lights are classified as cool lights.

Light fixture manufacturers typically measure the light waves emitted by various kinds of bulbs. They indicate these through color temperature readings and print them on the bulb’s packaging.

Here are the different color temperatures that common grow light lamps emit:

Incandescent bulbs – 2700K

High-Pressure Sodium Lights – 2200K

Halogen lights – 3000K

Clear Metal Halides – 4000K

LED lights – 5000-6500K

The list here provides you with a generalized estimate of color temperature ranges. Color temperature may vary depending on the individual manufacturer, so always be sure to check the packaging or ask the seller first.

Light requirements of plants

Plants need varying wavelengths of light to support all stages of their propagation. No single light wavelength can sustain foliage from its vegetation through its flowering and fruiting stage. Light requirement changes as plants go from one stage to another.

Let’s look at the general light requirements for plants under various stages of their growth and development. Remember that the exact requirements will vary depending on the type of plants you have.

Seed and germination stage

Cool blue lights with color temperatures of 5000-6500K allow seedlings to grow properly. The lights’ high energy content encourages seedlings to grow well and allows roots to flourish.

Vegetative Stage

This stage sees the emergence and growth of stems, leaves, and branches. A mixture of blue and red lights works well this time, with blue lights of up to 7500K being more dominant.

Reproductive, Blooming, and Fruiting Stage

Plants in the reproductive and blooming stage benefit the most from red lights with color temperatures of up to 3000K. Warm red lights have lower energy stores and trigger flowering along with a process known as photoperiodism. Plants that reaching fruiting may use a mixture of less blue lights and more red lights.

Do plants use all light spectrums produced by the sun?

No. Plants only absorb a few colors from the light spectrum emitted by the sun. These colors include red, blue, yellow, and green. Chlorophyll and carotenoids in plants are responsible for trapping these colors and turning them into chemical energy(9), (10).

Red is the color at the lower end of the light spectrum. Plants need this color to reproduce, flower, and bear fruit.

Blue is at the farthest end of the spectrum and has a high energy content, making it suitable for the early stages of plant growth and vegetation.

Yellow is found at the center of the spectrum. It gives off medium energy and is absorbed by secondary plant pigments such as carotenoids.

Green is also in the center of the spectrum. Chlorophyll reflects the green light waves off the leaves and gives most plants its green color.

Do different light spectrums do different work in plants?

Yes. Different grow light systems emit various kinds of light spectrums. Grow lights that use single monochromatic bulbs may have a different effect on plants than combinational lights that use mixtures of red and blue lights(11).

Predominantly red lights such as High-Pressure Sodium lights can trigger flowering and fruit-bearing in plants. Meanwhile, predominantly blue ones like metal halides can speed up the growth of young seedlings. A mixture of these two light systems can be good for long-term use as it supports plant growth in all of its stages. Note, however, that mixed light efficiency and its overall effect on plants will depend on how much red and blue lights are used.

How do plants use different light spectrums?

Plants use their pigments to absorb the light created by different light sources. They utilize the primary pigment chlorophyll and the secondary pigment carotenoids to trap light energy in and turn them into chemical energy.

Photosynthesis requires that plants absorb light with wavelengths of 400-700 nanometers. This requirement is supplied by the various light spectrum colors emitted by the sun or an artificial grow light source.

A color spectrum’s blue and red light waves get absorbed the most by plants. Chlorophyll is responsible for absorbing most of these spectrums’ rays and turn them into energy for later use in photosynthesis.

Carotenoids are secondary pigments that trap light from the orange and yellow spectrums. They pass on whatever they absorb to chlorophyll, which in turn will create energy out of these waves. Carotenoids are also responsible for the yellowish-orangey hues of leaves, especially during the fall season.

Different light spectrums and how plants use them will be further explained below.

Ultraviolet light (10nm-400nm)

Ultraviolet light is a part of the complete electromagnetic spectrum emitted by light sources. It lies after x-rays and just before the spectrum of visible light. It has a low range of wavelengths with only 10-400nm.

The sun naturally carries ultraviolet rays. However, the rays get screened by the stratosphere layer of the Earth’s atmosphere. As a result, most ultraviolet rays fail to reach plants. Which is a good thing because most plants are negatively affected by exposure to ultraviolet light(12).

Ultraviolet light is effective in killing microscopic life forms such as bacteria. But it can also have a deadly effect when plants absorb them. Ultraviolet rays can significantly alter processes needed to complete photosynthesis, thus depriving plants of their food and energy source.

The degree of plant damage that ultraviolet light creates vary depending on the type of plant and its nutritional state. Plants who have an abundance of water and food can better withstand the negative effects of ultraviolet light exposure.

Blue light (430nm-450nm)

Blue light is responsible for the continuous growth of germinated seeds, seedlings, and young plants. This light does a lot of things to plants that fire off their growth and development(13).

Photons in blue light are primarily responsible for triggering photosynthesis. This remains true even if the energy coming from its high-energy photons can get lost as compared to those lights with lower energy concentrations.

The stomata is a plant part consisting of tiny openings on the leaves. This regulates the flow of water and carbon dioxide throughout the plant. Blue lights help by opening up the stomata, thus improving the regulation of water and carbon dioxide and hastening the photosynthesis process(14).

Plants grown under blue lights have small, thick, and dark green leaves. Blue lights appear to inhibit upward growth, which is why blue light-grown plants are not tall and slender.

Greenlight (500nm-550nm)

Green light waves are typically reflected off by the leaves and stems of plants. This is because chlorophyll, the green pigment that aids in photosynthesis, doesn’t absorb these light rays.

There are good reasons why plants do not absorb green light but merely reflect them off. Experiments and researches have shown that plants grown under green lights did not thrive well because of a lack of photosynthesis.

Research from the University of Florida even concluded that seedlings must not be exposed to green light as it can potentially reverse stem growth and eventually stunt the growth of seedlings and young plants(15).

However, since green light waves lie in a low-energy place in the color spectrum, they are believed to promote continuous growth, flowering, and fruiting of plants with well-established and stable growth patterns.

Generally, green lights are not popularly used in indoor gardening because of its insignificant effects on plant growth and development at any stage of the propagation cycle.

Red light (640nm-680nm)

Low-energy red lights are useful to grown plants who are entering the blooming and fruit-bearing stages. They are also used to complement blue lights during the vegetative stage of plant growth.

Red lights are good for increasing the rate at which photosynthesis occurs. This is because red light waves fit in with chlorophyll absorption peaks, hastening the photosynthesis process and helping to enlarge plant size.

If rapid photosynthesis happens, vegetative growth increases followed by a rapid yet robust flowering and fruiting stage. Red light promotes flowering because it has a lower light intensity that can contribute to photoperiodism. Photoperiodism is the flowering response of plants to dim lights and total darkness(16). Indoor plants with exposure to darkness and warm, dim red lights bloom as they correlate this dimness and darkness to the natural nighttime when they are truly supposed to flower slowly.

Far-red (730nm)

Far-red light is barely visible to the human eye because it already lies at the farthest end of the visible light spectrum, and lies just before infrareds in the complete electromagnetic spectrum.

Plants are still able to absorb waves emitted by far-red radiation lights. Far-red waves are especially useful for a plant’s extension growth(17).

You might be familiar with how a plant looks when it is solely grown under red light from its seedling time. The plant looks elongated with slender stems and few leaves. Far-red light waves do the same thing to plants, influencing plant height, stem length, and leaf size in a similar way that red light does.

Some long-day plants greatly benefit from far-red waves when they are used together with red lights in photoperiodic low-intensity lighting. This type of controlled time lighting is used whenever natural days become short to help long-day plants bloom and flower.

Spectrum Control with Cannabis

Spectrum control refers to how your grow lights are engineered in a way that best utilizes the electromagnetic spectrum and the visible light color spectrum to your plants’ growth advantage.

Many growers who want to successfully cultivate cannabis often ask what the optimum spectrum control in cannabis growth is. There is no straightforward answer to this, though. As with all other plants, cannabis growth and development depend on a lot of factors that can be unique to each plant(18). Different spectrum mixes can produce a wide range of effects in a plant’s morphology at any given stage in the propagation cycle.

Growth Stages of Cannabis

There are four stages in the growth and development of cannabis plants. Each of these stages requires various sets of spectrum control to ensure that the cannabis plants will thrive until their adulthood.

Vegetation Stage

This stage encompasses the rapid growth ad development of cannabis from its infancy up until its young days. The goal of the vegetation stage is to produce healthy roots to become a stable foundation for when the plants get older.

Pre-flowering Stage

This stage starts with from the time the 12/12 flower cycle is initially started until small flowers become prevalent in the cannabis plant. Slowing of the plant’s overall rapid growth is also an indicator of this stage.

Flowering Stage

Cannabis plants go in full bloom 3-7 weeks after successful planting. Stem and leaf growth stop to allow the plant to focus on producing its large flowers.

Ripening Stage

When cannabis flowering gradually stops and the plant shifts back its focus on terpene and resin production, it is already entering the ripening stage.

Optimizing spectrum for ideal results

Cannabis plants can grow and bloom to their full potential with proper spectrum control. This will deliver adequate amounts of healthy light so that the plants will grow well and yield the best end-products after harvesting.

What people want in cannabis include the following:

Maximum oil yield for use in edible products and cosmetics

Maximum flower yield by weight

The potency of THC and CBD levels

Fragrance encapsulated in terpene concentration

To get the best results for these market needs, cannabis can be grown under ideal spectral light conditions.

Again, there isn’t a single spectral light mix to help cannabis grow to its best potentials. You can adjust the spectrum to fit your needs.

For instance, you can introduce small amounts of ultraviolet light to improve THC levels. Blue lights can be increased to enhance fragrance by improved terpene production. Far-red lights can be used at the near end of cultivation to trigger cannabis flowering.

Improving Cannabis Resin Content

Resin content, as well as oil to wax ratio, are all dependent on the cannabis flower’s density. You can improve the resin content by adjusting your grow light spectrum in the following ways:

During the vegetation stage, you must include a full spectrum of both blue and red lights. This will help promote maximum plant size growth. A red/blue light mixture of about 60/40 proportions is deemed ideal.

The blue light waves become extra important as your cannabis plants move on to the pre-flowering and flowering stages. Using a grow light system that emits predominantly blue lights ensures better resin yield.

The red lights may be decreased a bit when your cannabis plants reach the ripening stage. This is to increase terpene production, which is important for extracting fragrance from the plant.

Ultraviolet-B lights are needed to help increase both terpene and THC levels in the resin(19). These lights must be used throughout the cultivation period.

Ensuring Maximum Flower Yield

Total flower yield is typically measured by weight. Growers who are after the maximum total flower yield may want them because of the many commercial uses they can glean from cannabis flowers.

You can adjust your grow light system to ensure a maximum flower yield by increasing the amount of red light use throughout the entire cultivation period. Red light has been shown to trigger blooming stages in most plants, including cannabis. This is because of the reaction of plants to warmer, dimmer lights, combined with their natural flower-inducing reaction to photoperiodism.

Do not remove the blue and ultraviolet lights, though. These two lights are extremely necessary to balance out your grow lights system. Using red lights alone will not produce the best flower yield your cannabis plants are capable of generating. Adjust the levels as needed to avoid adverse effects of too much red light, such as overly tall plants and thin leaves and flowers.

Gaining Maximum Top-shelf Flower Yield

Grow lights for top-shelf flower yields ideally must have adjustable spectrum options so that you can easily control the amount of ultraviolet, blue, and red lights. High-quality flower yields need a frequent readjustment of the light spectrum to meet the needs of cannabis plants as they go through the cultivation cycle.

Short tight internodes during the vegetation stage require a decrease in the red/blue ratio. A good ratio to try is 60/40. This is increased to 70/30 or 75/25 during the pre-flower stage to prevent plant stretching.

The flowering stage is a critical time because you want your cannabis flowers to reach their largest possible size. The red/blue light ratio needed to do this is 80/20. While you can further increase the red lights to promote further blooming, it is not recommended due to the risk of lower quality resins and fragrance. Lower down the red/blue ration to 70/30 or 60/40 during the last two weeks of the ripening stage.

Can Any LED Light Be Used as a Grow Light?

LED lights specifically made for gardening are the best ones to use as grow lights. These lights are called horticultural LED grow lights and are most suited for indoor plant growing(20).

Horticultural LED grow lights emit only the specific light waves that plants can absorb(21). This is in contrast to normal LED bulbs used at home, which emit far more light waves and produce a brighter light for domestic use.

LED lights specifically made for gardening are best because they are energy efficient as well. Since they produce only the light that plants need, you save on energy consumption and ensure that they are doing their job of growing plants well.

What should I look for in LED Grow Lights?

The plethora of horticultural LED grow lights in the market have caused confusion as to which is working well for plants. Here are some key factors to keep in mind when shopping around for LED grow lights:

Materials Used and Durability – Lamp must be able to last for up to 10 years.

Low Heat Output – Lights must not easily heat up to protect plants from overheats and burns.

High-Quality Semiconductor Chip –Select a 3-watt chip for better conversion of energy to light.

Full Spectrum – Consider getting LED lights that offer full spectrum so that it can be used for the entire duration of plant propagation.

Do different light spectrums do different work in plants?

In general, red and blue spectrums affect plants in different ways. Red lights are best for the flowering and fruit-bearing stages of plants, while blue lights are typically used during the early stages of seedlings and young plants.

Many growers use a combination of red and blue light spectrums to power the growth of their foliage. The mixture of red and blue lights produces different spectrum strengths depending on the number of reds and blues used. These varying spectrums will ultimately be absorbed by plants and will work accordingly. Some combinations will cause plants to elongate and grow slender stems, some will assist in fruit-bearing, and some will allow seedlings to grow rapidly to adulthood.

How long should grow lights be left on?

Plants also need darkness to grow well(22). The notion that foliage must be left with grow lights on for 24/7 will lead to plant fatigue and overheating.

Sunlight only occurs during the daytime and is replaced by night. Hence, plants growing in a natural environment are routinely exposed to the darkness of the night. This should also be the case for indoor plants cultivated using grow lights.

Most flowering plants need grow lights for around 12-16 hours per day. Darkness of at least 8 hours is recommended as well(23).

Consider purchasing and installing an automatic timer that switches off the lights after a set time. This way, you won’t leave your plants under the lights too long should you forget the time to turn off the lights.

What is the best light spectrum for plant growth?

Red and blue light spectrums are the best lights for all stages of plant growth. Warm red lights promote the flowering of plants and continue to nourish them well until the fruiting stage. Cool blue lights have an intense energy that is best utilized for growing seedlings, strong roots, and young plants.

Other waves in the electromagnetic spectrum do little to no help in growing plants:

Ultraviolet spectrum alters photosynthesis and is therefore harmful to plant health.

Green lights may stunt stem growth and are generally only being reflected off from leaves, branches, and stems.

Orange and yellow lights are absorbed in minute amounts by plants and do not significantly provide a source of food and energy for plants.

How do we measure light?

Light can be measured in two ways: by wavelengths and by color temperature.

Wavelength is defined as the distance covered by a light wave’s shape until it repeats. The measurement is expressed in nanometers (nm). Visible light emits waves which vary in lengths:

Violet – 380-420 nm

Blue – 430-495 nm

Green – 500-550 nm

Yellow – 560-590 nm

Orange – 600-630 nm

Red – 640-680 nm

Far Red –690-750nm

Color temperature is the warmth or coolness of a particular light. It is expressed in Kelvins (K). This measurement is especially important for determining the warmth or coolness of different grow light bulbs.

Lights are classified as warm when their temperature is at 2700-3000K. These emit colors that range from red to yellow. Cool light, on the other hand, has temperatures of over 5000K and emits bluish to clear white tinges.

The Light Spectrum and Plant Pigments

Plants contain several colored pigments that perform several functions for plants(24). They primarily aid in absorbing radiation from the light spectrum.They are responsible for catching energy from the sun and artificial light sources. These pigments also regulate photosynthesis and make plant growth possible. And the pigments are also the ones who give color to a plant’s leaves, fruits, and flowers.

Specifically, the pigments contained in plants include the following:

  • Chlorophylls
  • Carotenoids
  • Phytochrome
  • Flavonoids
  • Betalains
  • Phycobilins
  • Rhodopsin
  • Flavins

Among these pigments, chlorophylls and carotenoids are the most involved in light capture, photosynthesis, growth, and development. We’ll discuss these two pigments further.

Chlorophyll (a)

Chlorophyll is a green pigment mostly found on plant leaves. Specifically, it is found within the inner membranes of tiny plant organelles called chloroplasts. Chlorophyll-a is the most active pigment in catching light waves and initiating photosynthesis(25).

Chlorophylls work by absorbing mostly red and blue light waves emitted by light sources. After absorption, chlorophylls move to an excited state where they produce higher energies. The light waves they absorbed will then go to the chloroplasts to initiate chemical changes within the plant. This eventually leads to food manufacture through photosynthesis.

Green light is also being taken in by chlorophyll. However, it reflects green light from the leaves and stems instead of absorbing it in.


Carotenoids are yellow, red, or orange pigments stored in a plant’s leaves, stems, flowers, fruits, and roots. They are pigments that lie within a plant cell’s plastids, a membranous organelle where chemical compounds are synthesized and stored. Carotenoids are responsible for the yellow-orange hues of certain leaves, stems, flowers, and fruits.

There are two main types of carotenoids: Beta-carotene and lycopene. Beta-carotene is responsible for the orangey color of vegetables such as sweet potatoes and carrots. Lycopene is what gives tomatoes their characteristic red hue.

Apart from giving color to plants, carotenoids also absorb light waves and transfer them to chlorophylls for photosynthesis(26). They also help protect plants from overheating by dissipating heat caused by the extra light energy they absorbed.

Choosing the Right LED Grow Light Color

LED light systems are popular choices for horticulturists and plant hobbyists because of their efficiency and energy-saving capacity. LED lights have the unique capability to adjust the light spectrum they emit to suit the needs of the plants. They also do not heat up as much as other grow light bulbs do.

You don’t have to adjust LED grow light color spectrums too much, as LED lights typically come in full-spectrum strength. But as a general rule of thumb, LED grow lights must contain the following wavelengths to support the entire plant cycle:

Blue LED – 400-500 nm

Red LED – 600-700 nm

Far-Red LED – 700-800 nm

Some Green LED – 500-600 nm

A few white LEDs

A few Ultraviolet and Infrared LEDs

Choosing the Right Color Temperature for Fluorescent Lampsand HID Grow Lights

Fluorescents and HID lights are dubbed as the traditional grow lights growers have been using long before LED came along. These two types of light can emit either bright daylight tones or soft yellowish lights.

Selecting the right fluorescents and HID lights all boils down to their color temperature.

If you have seedlings or young plants in the germination and vegetative stages, your best bet is a lamp with a color temperature of 5000-7500K. These are dubbed cool blue lights and resemble natural daylight hues.

For plants in the flowering and fruiting stages, lamps with color temperatures of 2000-4000K are ideal. These lights emit warm soft reddish hues. These warm lights promote blooming and fruit-bearing.

Best Grow Lightsfor Seedlings & Clones

Seedlings need intense energy from light sources to grow properly. Hence, they benefit the most from using cool blue lights. These lights fall in the 5000K and above color temperature range. Blue lights emit a high amount of electromagnetic energy that tiny seedlings need to fuel their growth and development.

Grow lights that emit blue hues include the following:

Fluorescent lights – Light intensity is fine and it doesn’t heat up too easily.

Metal halide bulbs – Be careful because they can get too hot and potentially burn the seedlings.

Note that these lights must emit hues that resemble daylight to be effective.

Best Grow Lights for Vegetative Growth

Light requirements shift as plants enter the vegetative stage after being seedlings. They need strong blue hues that are more intense than those used during the germination and seedling stage.

Grow lights that are best for vegetative growth are the same as those used during the seedling stage. You can continue to use fluorescents and metal halides for cultivating your plants. However, you must adjust the color temperature up to 7000K to gain the best results.

Fluorescent lamps aren’t as intense as metal halides, so they are great for use with herbs and leafy green vegetables. Most other plants are fine with metal halides.

Best Grow Lights for Flowering and Fruiting Stages

Less blue spectrum is needed as your plants finally enter the flowering and fruiting stages. You need to adjust your grow light system so that the plants get exposed to the redder spectrum during these times.

Low-energy red lights in the 2000-3000K range promote blooming by mimicking the processes plants undergo during a shift from daylight to nighttime. Photoperiodism, or plants’ reaction to lengths of day and night, come into play here as well. Flowering is triggered by the dimmer red lights and periods of darkness in between.

Consider swapping your metal halide bulbs for some high-pressure sodium lamps. These fixtures provide light that leans more in the red spectrum.



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