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What Color Light is Best for Plant Growth?

Whether it is lack of decent garden or yard space or if you live in a concrete jungle stacked with apartments, indoor gardening is the only way for some people who like to grow plants. These can be small decorative plants that brings out some green in the house or plants that grow flowers and food. One important and often misunderstood area in indoor gardening is lighting. Plants need light to grow. But what color light is best for plant growth? We will try to explore more about light color of light that plants require in this guide.

How Plants Use Light?

It is time to revisit our high school biology and understand how plants use light. This is a critical step if you want to successfully grow indoor plants and also select the right light and color.

Plants undergo a process known as ‘Photosynthesis’ that converts light energy into chemical energy. And the most abundant and obvious source of light for plants is Sun.

When sunlight hits the leaf or stem of the plants, they use the surrounding carbon dioxide and the energy from photons to convert it into hydrocarbons or sugars with a neat little byproduct that we call Oxygen.

There is actually a lot going on in the plants during photosynthesis that involves water, chloroplast, chlorophyll, carbon dioxide etc. but this is just the gist of it.

It is clear that light is the main source of energy for plants to perform basic biological functions. So, if you are planning to grow plants indoors, then you have to focus on the amount of light, type of light and also the color of light to successfully enable the stimulation of photosynthesis.

Electromagnetic Spectrum, Visible Light and Colors

While we see light in terms of color and brightness, plants see it as frequency, wavelength and spectrum. The Electromagnetic Spectrum consists of all the frequencies electromagnetic radiation, of which the visible light is also a part of.

Other types of frequencies in the spectrum are: Radio, UV, Infrared, X-Rays, Gamma etc. Sun is a natural source of electromagnetic radiation that contains primarily the visible light but also other frequencies (UV and infrared).

Speaking of visible light, it is a tiny portion of the electromagnetic spectrum with wavelength range of 400nm to 700nm (or frequency range of 750 terahertz to 450 terahertz). Humans can see only these frequencies in the entire electromagnetic spectrum and all the colors in the World fit in this range.

Sunlight consists of all the wavelength corresponding to visible light. That is the reason it appears White in color. Based on this analysis, it is wrong to assume that White light is the best for plant growth because each wavelength has a different impact on plants.

Effect of Light Color on Plant Growth

Let us now see the impact of different wavelengths (light colors) on plant growth.

Blue Light

Blue wavelengths are the most useful for plants as they help in the movement of chloroplast in plant cells. This in turn helps in transport of oxygen.

Red Light

The next important wavelength is Red. When we expose plants to red wavelength, the number of leaves increases, the plant blooms and quality of fruit will be better. Both Red and Blue wavelengths are not very useful on their own but only when we combine them together.

As a matter of fact, the ratio of Red and Blue must be in favor of Red i.e., Red should be slightly more than Blue.

Green Light

A common misconception with green wavelength is that plants reflect all green light and hence appear green. This is true but only to some extent. The green wavelengths penetrate deeper into the photoreceptors while other wavelengths can’t do that. You should have small quantity of green light in the spectrum.

Ultraviolet (UV) Light

Just as humans are sensitive to UV Radiations, UV Light similarly affects plants as well. Even though the Ozone layer filters out most of the UV Radiations from Sunlight, there is some UV Lights that enters the Earth’s atmosphere.

Severe exposure to UV Lights can damage plants at cell level. But there are some benefits to UV Light such as small exposure will stimulate the production of resins, oils and protective antioxidants that gives additional flavor.

When we expose Cannabis to UV Light, it produces a protective resin against harmful rays and makes the leaves more potent

Infrared Light

While plants do not use Infrared Wavelengths for growth, but it plays an important role in photomorphogenesis, a growth and developmental change in plants. Exposure to small quantities of IR Light will speed up the plant growth and also improves blooming.

Other Wavelengths

The impact of other wavelengths such as violet, yellow, orange etc. is very less on plant growth.

What Color Light is Best for Plant Growth?

Now, the important question: What Color Light is Best for Plant Growth? Simple answer is a combination of red and blue lights is very good for good plant growth. The Red Wavelengths help in increasing the biomass (additional leaf growth) while Blue Wavelengths control the flow of chloroplasts in the cells (which is responsible for oxygen transmission and also regulates the stomata opening).

This is true for a good variety of Plants. Hence, you can find some combination of Red-Blue Grow Lights in the market. Other popular color Full Spectrum Grow Lights. As the name suggests, it is essentially a cool or warm white lights and it emits some proportions of all the important wavelengths.

Cool Lights are mainly Blue with some red, yellow and green wavelengths while Warm Lights are predominantly Red with hints of Blue, yellow and green.

Another popular option among indoor gardeners is to mix and match different colors of light at different stages of the plant.

Types of Grow Lights

LED Lights

One of the popular types of grow lights for indoor gardening are LED Lights. You can get all the color and even full spectrum options with both cool and warm white. They are also cheap and you can precisely control the color and amount of light falling on a plant or on a specific area.

Fluorescent Lights

Before the wide spread availability of LEDs, fluorescent lamps were a popular choice for indoor gardening. Most fluorescent Lights produce slightly bluish colors, so leafy plants benefit from these lamps.

Fluorescent Lights also lasts relatively long and doesn’t produce much heat. Hence, gardeners use these lamps to save energy as well as space.

High-Intensity Discharge Lights

HID or High-Intensity Discharge Lights are really bright lamps, meaning they could cover a wide area with a single light. HID Lights are usually white with slightly yellowish tint, making it suitable for all kinds of plants.

Indoor gardeners with large plantation usually prefer HID Lights due to their light coverage.

Incandescent Lights

One of the least and often ignored lights for indoor plant growth are incandescent lights. Most of the energy of incandescent lamps is converted as heat and even the light has significant amount of infrared wavelength.

Their light has high yellow color, making it less usable for plants. Even though some gardeners use these lights due to their low cost, overall, the light isn’t great for plant growth, it doesn’t make the plants grow fast and lots of energy is wasted (as heat and IR).


Indoor Gardening is sometimes the only way for some people to grow plants. Getting sunlight indoors is quite difficult in today’s apartment culture. In such situations, investing in proper grow lights to help the plants grow indoors is a good choice. But what color light is best for plant growth? We saw answer to this question and we also covered other important topics corresponding to light and plants relationship, impact of colors on plant growth and different types of lights.

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