How Does Different Color Light Affect Plant Growth?

When we look at light, most of us see just that, light but light consists of many wavelengths so how does different color light affect plant growth?.

There is a full color spectrum in light, and each color affects plants in their various stages of growth.

Each color spectrum can affect how marijuana plants grow in each stage, and if you are using indoor LED grow lights, you can control the color spectrum and grow large, healthy plants that produce a high yield.

There is no best all-round spectrum for growing marijuana, but you can set up your grow room to have the best spectrum for your particular needs.

Why do Marijuana Plants React to Light Spectrums

Why do Marijuana Plants React to Light Spectrums?

You may be wondering why marijuana plants need a full light spectrum. When grown outdoors, they receive full sunlight, so they get that full spectrum naturally. The natural light spectrum changes throughout the day, so plants get the color spectrum they need at all growth stages. When grown indoors, you need to provide them with that same light, so they grow just as well as they would outdoors.

There are two main light spectrums that your plants will need to grow properly: blue light and yellow/red light.

  • Blue Light – During the vegetative stage, your plants will need the blue light spectrum. This is going to insure that they grow short and fat, and have large, healthy leaves. When grown outdoors, this is the summer growing period. Once plants have completed this stage, they need a different light spectrum.
  • Yellow/Red Light – When your plants are in the flowering stage, yellow/red light will encourage them to start to grow taller, and encourage budding. Switching to yellow/red lighting will help them to flower faster than when using the blue light.

When you monitor the color ratios in the light spectrum, you can help your plants to grow larger, in a shorter period of time. Basically, you are controlling the light, and telling the plant when and how to grow.

Is All of this Necessary?

This may seem like a lot of unnecessary work, and some growers will agree. You can get decent plants as long as they get some degree of red and blue light. They will grow normally. But, if you want significantly higher yields, it is best to train your plants in their growth stages so you can get as much out of them as possible, and get high quality bud. If you have the tools at your disposal anyway, in this case the LED lighting, there really is no sense in not using them to your advantage.

Color Spectrums and Strains

Color Spectrums and Strains

One thing to keep in mind is the strain you are growing. Different strains react differently to the light color spectrum. Some plants may be very much affected, while other strains aren’t affected at all. Also, sometimes, the plants just need light, period, and they don’t care about the color.

Without enough light, your plants can grow tall and lean, even if there is a lot of blue light, because they are still trying to get more light. On the other hand, if they are getting a lot of yellow light, they will be shorter because they have plenty of light and don’t need the blue light to grow taller.

Other Light Color Spectrums

Blue and yellow/red light spectrums aren’t the only color spectrums that can affect plant growth. Let’s take a look at the other types of light that are commonly used when growing marijuana indoors.

  • UVA/UVB/Ultraviolet Light – This lighting is often classified as being part of the blue spectrum, but it also has its own particular effects on plant growth. UV lighting can increase the THC levels in your plants. Most grow lights do produce UV rays, but not as much as the sun. Reptile lamps are a good source of UV lighting for indoor growing, and there are also new LED lights that have UVB, which has light in the infrared spectrum.
  • Green Light – Green light is not the most effective for photosynthesis, but it can affect plant growth. It should be used during the seeding and vegetative stages, as well as in the beginning of the flowering stage. It is not necessary to use green light, and you may or may not see any noticeable effects when using it.


Just because plants do react to the various color spectrums in light, it doesn’t mean that you have to go out and spend a lot of money on lighting gear. If you can only use one spectrum, that is okay, but be sure to use the right spectrum for what you are trying to achieve.

If you want bigger yields, it is best to use the red light spectrum for the entire grow. This is often done with great results, and some growers will even say that it is their preferred grow method.

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