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artificial purple grow light

What Color Light Is Best for Plant Growth? Grow Lights Guide

What color light is best for plant growth is an important question that needs to be answered if you’re growing plants indoors or during time periods when there it not much sunlight around.

We already know that light is absolutely essential for growing plants indoors, it’s only a matter of establishing how colored lights affect plant growth. It’s an absolutely essential component of hydroponics systems, too.

In this post we’ll talk about what color light is best for plant growth and why. You’ll be able to get the best grow lights in no time. Just don’t be scared by the price tags. Most of the time those things are not cheap at all.

What Color Light is Best for Plant Growth? Short Guide

I will give you the short answers, in case you don’t want to read a whole article on what color light is best for plant growth:

  • white LED light, which is emitted by full-spectrum LED grow lights, is the best light for growing plants indoors – there are different options to choose from: 3000K/4000K (warm) LEDs work well for all growth stages, including flowering, while the vegetative stage does very well with the 5000K to 6500K range
  • red/blue LEDs are a perfect choice for greenhouses because greenhouses already receive a certain amount of sunlight
  • fluorescent lights work for small plants and they’re great for microgreens, the best are the 5000K to 6500K ones
  • HIDs (high intensity discharge lamps) are fantastic, expensive, a definite top choice, but they will require their own ventilation system because they will increase a room’s temperature
  • incandescent lamps are a no-go

Sunlight is King

plants growing in natural sunlight

Plants growing outside in natural sunlight

Light is the component that leads to photosynthesis. Without this component, no matter how amazing your system is, you can’t grow healthy strong plants. It’s kind of a big deal.

But let’s get one thing clear right from the beginning of this article on what color light is best for plant growth: there is no substitute for the power of the sun. The most powerful lighting source for plants will still be the sun, probably for many decades to come, as it was until now.

Nevertheless, if we can’t grow plants outdoors, we can still do our best to provide them with the best grow lights for a plentiful yield.

Thus,

The direct answer to what color light is best for plant growth is that white LED light is the best. White LED light is actually given by full-spectrum LED grow lights.

What Color Light Is Best for Plant Growth? Blue, Red or White Light?

Let’s eliminate one candidate when it comes to answering what color light is best for plant growth.

Incandescent lamps shouldn’t be an option at all, they’re quite inefficient.

A study from Bates College established that plants grown under LED lights had a higher increased growth rate compared to those grown under fluorescent lights. The study also concludes that LED grow lights produce the necessary wavelengths of light needed in plant growth.

Actually, fluorescent light can pretty much only be used for growing microgreens and for smaller plants. In that particular situation fluorescent light, 5000 to 6500K, works well because microgreens are immature plants, they only need to be grown for 2-3 weeks before being ready for harvest.

A popular type of fluorescent lights are the compact fluorescent lights (CFL) because they have a longer life and use less electricity. Plus, they’re cheap. If you have a limited budget, you should try CFLs.

HIDs (high intensity discharge lamps) are top pick for serious growers but they require a big budget and you will have to get their own ventilation system since they significantly raise the room’s temperature. They’re pretty much on another level. If we were to talk about the best grow lights, HIDs will be at the top of the list.

Still, the focus of my article on what color light is best for plant growth is fully focused on LED grow lights. I told you that full spectrum LED grow lights are the easiest answer to what color light is best for plant growth.

But how does colored light affect plant growth? Not all lights contribute to photosynthesis equally.

How Do Colored Lights Affect Plant Growth?

It’s the time to understand what role each of them plays, we’ll see exactly how colored lights affect plant growth by talking about the two most important lights for plants.

Red Light

Red wavelengths initiate seed germination and root development.

Fluorescent lights produce the red wavelengths, which is why they can be used for growing microgreens indoors.

Let’s state the important: red light is the most efficient for photosynthesis and basically nothing can be done without the red light.

Does that make it the answer to what color light is best for plant growth?

The simple answer is no. The truth is that having only red light would result in poor growth. A result could be plants with elongated stems.

Blue Light

So, blue is added to the red in order to maintain the proper shape of plants, to make them grow compact.

Blue light is required for plant growth.

Bluelight photoreceptors influence chlorophyll production and regulate a plant’s retention of water.

We can’t only use blue light either because plants’ growth will be negatively affected.

Which is why there must a combination of blue and red, LED manufacturers offering a fixed ratio of red to blue for greenhouses.

thegreensunshineco.com warns us that too much blue will actually stunt plant growth. And that many growers actually prefer “warm white” LEDs, 3000K/4000K (warm) LED spectrum.

If we were to ask is red or blue light better for plants, the answer would be that there must always be a combination of red and blue for productive plant growth.

So, another answer to what color light is best for plant growth would be: red and blue. Or white light if you choose full-spectrum LEDs.

Yellow and green lights have minimal effect.

Are Full-Spectrum LED Grow Lights the Best for Plant Growth?

full-spectrum LED grow lights

Basil plant growing in full-spectrum LED light

The simplest answer to give if you’re wondering how do colored lights affect plant growth is: go for full-spectrum LED grow lights or go for red/blue spectrum LEDs.

LED stands for light-emitting diode. Their main advantage is that they offer more light with less power consumption. It makes them very efficient and enable us to save on energy costs. Their longevity of 25,000 to 30,000 hours is their second biggest advantage.

Choosing to get full spectrum LED grow lights is the best general solution to growing plants indoors by using just artificial light.

I used the word mimic because the artificial light doesn’t in fact come close to natural sunlight. It’s not surprising considering that sunlight is complex, it’s not only a matter of producing a Color Rendering Index (CRI) over 90.

Full-spectrum LED grow lights are the obvious choice when it comes to answering what color light is best for plant growth because these are the ones that mimic the natural light from the sun.

The second option is to go for red/blue spectrum LEDs but that’s recommended mainly for greenhouse, spaces which already receive a certain amount of sunlight.

According to lumigrow.com, there is no such thing as full spectrum LED grow lights, although the general consensus is that full-spectrum LED grow lights are the best for growing plants indoors. Let’s see what’s with these 2 statements.

Well,

Their argument is that not all full-spectrum LED grow lights are created equal because not all of them are custom-tailored for rigorous plant growth.

From that, we can draw our own conclusion: we should pay attention when shopping and choose LED grow lights that have been designed for plant growth. Most are not cheap.

Red/Blue LED Grow Lights: Great for Greenhouses

red and blue grow lights

Basil plant growing in artificial red and blue light

This combination is also known as narrow spectrum LED lights. They’re really great and continue to be popular even nowadays.

These are the ones that give off a pink or sort of purple hue. In comparison, full-spectrum LEDs render a white light.

It’s a really good choice if you’re placing them in a greenhouse where a narrow spectrum is desired because the plants are already receiving the full spectrum of light from the sun.

Adjustable Spectrum LED Grow Lights: the Futuristic Choice

These actually sound quite futuristic and they might be exactly what some growers are looking for.

This type of LEDs allows users to wirelessly calibrate the spectrum, making it possible to speed up certain stages, like speeding up flowering times.

How to Use Grow Lights

Usually, artificial lighting for plant growth is used for about 14 hours on average. The rest of 10 hours is lights off. Plants need their rest to metabolize nutrients.

That’s the general rule but there can be exceptions because some plants might need more time under grow lights, while others might need less.

For example, hydroponic lettuce might be an exception to the lighting for 14 hours on average knowledge. Growers might leave the artificial lights on for 16 to 18 hours and only 6 to 8 hours off. Lettuce is definitely a long-day plant.

On the other hand, strawberries are short-day cycle plants that need longer periods of darkness. Short-day cycle plants should not be exposed to more than 12 hours of grow lights.

And there are also neutral plants, which are pretty much in the middle, between long-day and short-day plants. These can be mixed and grown together with either of the two categories.

In hydroponic systems, some choose to use a timer to set it up to their lights.

The placement of the grow lights is also important, you should pay attention to that, too.

FAQs on What Color Light Is Best for Plant Growth

To make things even more simple, let’s answer some frequently asked questions about what color light is best for plant growth.

Q. Is red or blue light better for plants?

Red light is the most efficient for photosynthesis, while blue light influences chlorophyll production and regulates a plant’s retention of water. They’re both essential for plant growth but we can’t say that red or blue light is better for plants because these two need to works together for successful plant growth. One can’t go without the other, otherwise plants’ growth will be negatively affected.

Q. Is white LED light good for plants?

Absolutely yes. White LED light is the best for plant growth because it’s the option that imitates sunlight. While it doesn’t come close to the complexity that light from the sun represents, full-spectrum LED grow lights are one of the best and most-energy efficient options for indoor gardens. It’s also the answer to what color light is best for plant growth.

Q. Will regular LED lights grow plants?

No. You absolutely need to get LED grow lights, which are designed for plant growth by maximizing red & blue light and by mimicking sunlight. Regular LEDs don’t emit enough of the light that plants require.

Q. Will 5000K LED lights grow plants?

Some growers consider the 3000K/4000K (warm) LED spectrum to be a decent growth spectrum, it can be a very good range for all plant growth stages. 3000K is very good for flowering. Others go for the 5000K to 6500K LED spectrum to grow plants. 6500K light is better than 5000K but, generally, both options work great for growing plants, especially for the vegetative growth stage.

And with that, I think we’re pretty much done on everything related to what color light is best for plant growth and how colored lights affect plant growth.