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You are here: Home / Grow Light Advice

What Color Light Do Plants Grow Best In?

Last updated September 17, 2022 By Steven 21 Comments

Best Light Color For Plant GrowthThe short answer is:

Blue light.

But it’s not quite that simple.

For one, plants grow great in natural sunlight. Sunlight isn’t blue. It is…yellow? White?

Wait, what color is sunlight, exactly?

That’s a bit of a trick question.

Sunlight contains all colors of the light spectrum. Technically, that makes it white light.

This means it contains blue light. Among all other colors.

It also contains red and yellow and green. Plants like to have those colors as well.

Especially red.

To make it more complicated, the addition of red to blue light makes plants grow far better. Blue on its own works. Red on its own doesn’t do much. Red with blue is ideal.

How much of each?

It depends on the plant and the current stage of its growth.

That’s getting ahead of ourselves.

Let’s first look at why blue and red are most important and what role the other colors play, if any.

Contents

  • 1 Plant Growth Under Different Colors Of Light
      • 1.0.1 Ultra-Violet
      • 1.0.2 Violet
      • 1.0.3 Blue
      • 1.0.4 Green
      • 1.0.5 Yellow
      • 1.0.6 Orange
      • 1.0.7 Red
      • 1.0.8 Far Red (Infrared)
  • 2 Under What Color Light Do Plants Grow Best?
    • 2.1 What Color LED For Grow Light?
      • 2.1.1 Is HID Light A Good Color For Plant Growth?
      • 2.1.2 Do Fluorescent Bulbs Have Good Light For Plant Growth?
    • 2.2 How Well Would A Plant Grow Under Pure Yellow Light?
    • 2.3 Best Light Spectrum For Clones?
  • 3 What Color Light Plants Grow Best In: Final Thoughts

 

Plant Growth Under Different Colors Of Light

different colors of light

As mentioned, plants grow best under a mix of red and blue light. The ideal ratio is somewhere around 5:1 red to blue.

But it does vary, depending on the plant and the stage of growth.

And remember: red light without the blue light is actually worse than blue light without any red light.

Confused?

Let’s look at the different colors of the visible light spectrum, plus the two colors just on either side of the visible spectrum, and see exactly how they impact the growth and development of plants.

visible light spectrum

Ultra-Violet

UV light is harmful to plants, just like it is to humans. There is a concern that this light can cause cancer, with prolonged exposure. That said, in being harmful, it can actually bring about positive side effects.

For example, when cannabis plants are exposed to UV light, they create resin to protect themselves from the harmful rays. This makes the buds more potent.

Violet

On its own, violet light has a limited effect on plant growth, but it is very useful when combined with red and blue light. The addition of violet light enhances the color, taste and smell of plants.

Blue

Blue is the most important light for plant growth, because it is readily absorbed by chlorophyll and converted into energy through photosynthesis.

That said, blue light on its own is not nearly as effective as blue combined with red. And you want far more red than blue light.

Green

Plants appear green, because chlorophyll does not absorb much green light, like it does other colors, and instead reflects it back at us. Based on this, it is easy to assume that plants do not make use of green light for photosynthesis.

Most websites do exactly this.

The truth is, most simply rewrite something they read elsewhere, without actually knowing anything about, or doing any real research on, the topic themselves.

But it isn’t quite true.

Plants have other photoreceptors that are responsible for photosynthesis, besides chlorophyll. And those other photoreceptors do absorb green light. If your plants get no green light at all, they would not be able to reach their full potential.

Even more importantly, green light penetrates deeper into the plants than other colors, so it reaches photoreceptors that other colors can’t.

Plants may not need nearly as much green light as they do red and blue, but they do need to have some. The action spectrum for photosynthesis proves this. Make sure you provide it for them.

Yellow

Plants make the least use of yellow light, but they do use it as well. Give them some, but they won’t need much.

Orange

Orange light is used like red light. It is not the ideal wavelength that a darker red is, but it is still absorbed like red. You want to provide some orange light, but more light that is a darker red than orange.

Red

Red is the second most important wavelength of light for plants. On its own, red is actually not all that effective, but when combined with blue, it becomes incredibly important.

In fact, you want far more red than you do blue, especially during the flowering stages of growth. Adding red light leads to stronger growth with more leaves during vegging and far better fruit and bloom production during flowering. Not only do you get higher yields, but also higher quality yields.

Far Red (Infrared)

Far red light is not absorbed much, but it plays an important role in plant growth and development. The ratio of red to deep red signals to the plant when it should start germination and also regulates flowering time.

 

Under What Color Light Do Plants Grow Best?

Colors of the visible light spectrum

Plants grow best when they have all colors of light. They want mostly red and blue (with about 5 times as much red as blue), with a good amount of light in every other color as well.

So what does that mean when it comes to grow lights?

 

What Color LED For Grow Light?

Many manufacturers of LED grow lights still subscribe to the outdated notion that plants need only red and blue light. As a result, they make “purple” lights with only red and blue diodes.

Stay away from those lights.

Instead, these two types of lights do the best job:

  • lights with mostly red and blue diodes, but also a decent amount of all-white diodes mixed in
  • full-spectrum white LED grow lights (like COBs or quantum boards)

There are plenty of good options when it comes to the first, but far fewer for the second.

The best lights that feature red, blue and white diodes are the BestVA LED lights. They are more expensive than many other brands’ though.

A good budget alternative is the King LED line of lights.

For all white lights, check out the Spider Farmer lights.

To be honest, I prefer a light that does not only have all-white COBs, but supplements them with red, blue, UV and IR diodes. That gives you an even better spectrum than pure white light and makes for an absolute flowering monster.

The Phlizon COB Series are the best lights at combining CREE COBs with additional diodes. These lights are basically equivalent to the much more expensive Optic LED lights, but cost half as much.

 

Is HID Light A Good Color For Plant Growth?

Traditionally, HID light meant either high-pressure sodium (HPS) or metal-halide (MH) light. The former contains a lot of red light, but virtually no blue, while the latter contains a lot of blue light, but virtually no red.

As a result, best results are achieved when both types of bulbs are combined to give plants all the colors they need. But that results in a lot of bulbs, which really drives up energy costs and heat. It also means you need a lot of reflectors and ballasts.

Using MH bulbs for vegging and HPS bulbs for flowering is the most common solution, but it is not ideal. Even though plants want more blue during vegging, they still benefit greatly from also having red light. And the reverse is true during flowering. They need tons of red, but still want some blue.

It is for this reason (among others, like operating cost and simplicity), that I much prefer LED and generally recommend LED grow lights over HID, since they don’t even really cost more these days.

That said, if you prefer HID, there is now a great option.

It is a newer type of HID light that combines the two spectra: it has a lot of red like HPS, but also a lot of blue like MH.

This type of bulb is called ceramic metal halide (CMH). If you want to go with HID light, CMH light is by far the best option.

See which fixtures are best here.

 

Do Fluorescent Bulbs Have Good Light For Plant Growth?

Fluorescent lights give off white light. They generally tend toward cooler light (i.e. light with more blue in it), but warmer bulbs (with a higher red content) are available.

Learn which fluorescent bulbs are best here.

 

How Well Would A Plant Grow Under Pure Yellow Light?

I get this question a lot. The quick answer is: not well at all.

The reason I get this question is that people see sunlight as “yellow.” It is not.

Sunlight is, in fact, white light, that is made up of every single color. It contains yellow light and this is the wavelength that is most visible to us, which is why it appears yellow.

Light similar to sunlight can work great to grow plants, but purely yellow light will not. Ideally, you actually want light with less yellow light than sunlight, since much of it is simply not used by plants.

With sunlight, that does not matter since it is a free energy source. But if you are paying to create the light (as you do with a grow light), what is the point in paying for so much yellow light, if it is not even going to be used?

 

Best Light Spectrum For Clones?

The best light spectrum for clones is actually the same as the best spectrum for any other stage. You’ve probably read that clones want blue light, but that is only partially true.

They do need a lot of blue light, but they also need the other colors. The ideal spectrum for plants includes a lot of blue light already, so there is no need for a special spectrum for cloning. Just use what plants already like naturally.

The only thing to pay attention to is the strength of the light. For cloning, you need far less power than for vegging, and especially for flowering. If you use the same light throughout all stages, make sure to dim it when cloning or raise it higher, to ensure the delicate clones are not burned.

If you want to by a light specifically for cloning, get one that covers a much smaller area than you need and hang it higher, to increase the coverage area. This reduces the intensity of the light and makes it safe for your clones.

For example, if you are cloning a 4×4 area, get a light that flowers 2×2 to 2.5×2.5 and hang it higher to increase its coverage to 4×4.

 

What Color Light Plants Grow Best In: Final Thoughts

Plants grow best in light that includes all wavelengths. This means white light, which includes all of the colors. Since plants do need more red and blue than other colors, grow lights that supplement all white diodes with additional red and blue diodes are ideal.

We gave you several good options to check out. Among them, Spider Farmer are the best. They are currently the best value grow lights on the market, period.

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Reader Interactions

Comments

  1. Mostafizur Rahman says

    September 21, 2019 at 22:00

    So, what light spectrum is best for Cactus? And which type of LED lights are best for Cactus?

    Reply
    • Steven says

      September 22, 2019 at 00:41

      I would just go with white light. It works for everything, since that’s what the sun is. Take a look at the Spider Farmer lights: https://growlightinfo.com/spider-farmer-sf-led-grow-light-review/

      or Phlizon: https://growlightinfo.com/phlizon-cob-series-review/

      Reply
      • Mostafizur Rahman says

        September 22, 2019 at 02:12

        One more question, What do you think the ideal distance from the light source to the cactus? As most of the cactus like more heat and intense light, I think there is less possibility to burn the cactus if the light set too close (like 5″ to 6″). What do you think?

        Reply
        • lana says

          November 6, 2019 at 16:18

          I have a question I am doing a science experiment on what type of light would a plant grow the best in what does HID have to do with plants and different kinds of light

          Reply
          • Steven says

            November 7, 2019 at 02:22

            It’s in the article.

          • Anonymous says

            February 19, 2020 at 08:30

            why tho

  2. Ruby YAO says

    December 10, 2019 at 16:47

    I would like to cite this as a source for my project but I don’t know your last name. Can you please tell me what it is?

    Reply
    • Steven says

      December 11, 2019 at 01:37

      McCabe

      Reply
      • Ruby YAO says

        December 19, 2019 at 16:25

        Thanks

        Reply
      • Dillion j DeShazer says

        September 26, 2020 at 19:39

        ironically im doing the same thing, glad i found this

        Reply
        • Anonymous says

          November 15, 2020 at 12:17

          Same

          Reply
          • anomynous says

            October 24, 2021 at 20:54

            same bro

  3. Perry says

    February 14, 2020 at 17:49

    Question I have is for a philizon type LED…namely Wills which I believe to be the exact same light … question is for germination and seedlings up to flowering is it best to run just the blue red switch and kick on the so called ‘Stronger’ switch for flower and fruit? which means turning on the COBs. I am growing super hot peppers in a grow tent because I have a white fly problem here in FLorida and for years have not been able to win the battle so this year I switched to indoors. But there is little info about the best settings and height for this. So far I am happy and the seedlings are happy with just the blue/red switch on and its at 40″ height. I know if its working go with it but if I can make it better I’d like to know. I did cook an early set of seedling with full blast but that was more my fault as I didn;t aclimate them from ambient germination to blasting light. Any thoughts greatly appreciated. Thanks for the quality info!

    Reply
    • Perry says

      February 14, 2020 at 17:51

      I should have included right now I am 18hours on and 6 off and plan to go 12/12 later when its time to flower. Thanks again.

      Reply
    • Steven says

      February 15, 2020 at 00:58

      I don’t really know how much light peppers need, but if they’re doing fine without the COBs on, there’s probably no reason to switch. But if you’re curious to see if they’ll do better, go ahead and give it a try for a day or two and see how the plants respond.

      Reply
  4. Amy says

    September 11, 2020 at 16:00

    I cant seem to get a sraight answer in all the things ive read about when should i use just the red lights. Do I use in the morning? All day? Or at night? Or even throughout the dark hrs? I have the led full light specrum ones that also has what they call as the flowering. But never specify what time of day\ night to use it. Everyone just says all are needed.

    Reply
    • Steven says

      September 12, 2020 at 01:55

      Use the full light spectrum for 12 hours per day. You should never use just the red lights.

      Reply
  5. Amy says

    September 11, 2020 at 16:06

    I appologize im growing cannabis and trying to get the correct lighting sequences to ensure best production and growth. And of course happy healthy plants

    Reply
    • Elizabeth says

      June 7, 2021 at 21:49

      Amy, how did it turn out for you??

      Reply
  6. Anonymous says

    April 10, 2021 at 17:36

    I am doing an experiment just for fun. Is putting Red, Blue, Yellow, Violet and White lights healthy for Roses?

    Reply
  7. Anonymous says

    November 4, 2022 at 02:11

    me im a monkey

    Reply

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