LED Grow Lights: How Does LED Color Spectrum Affect Cannabis Plants?

by Nebula Haze

Did you know that the “color spectrum” of your LED grow light affects your cannabis plants? Light contains many colors, and this mix of colors is known as the color spectrum of light. Unlike most other grow lights, LED grow lights allow you to specify custom light spectrums (or “spectra” another way to write the plural of “spectrum”) which change how a cannabis plant grows, including with germination, growing new leaves and stems, and most important to growers, how buds grow (their potency, final yields, and overall bud quality or appearance).

The light spectrum, or mix of colors, contained in LED grow lights affect cannabis plant growth, including bud development

Photosynthetically Active Radiation (known as PAR) is a measure of light in the 400-700nm range.

Are the results of growing cannabis under LEDs different from those using other kinds of grow lights? What about the sun? The answer is a resounding yes. Unlike other grow lights, which have a relatively “set” spectrum based on the chemical reactions that cause them to create light, or the sun, which has a spectrum you can’t really affect, LEDs allow you to make a fully custom light spectrum.

And LED grow light companies have been working directly with cannabis growers for years to research how spectrum affects cannabis plants. They’ve discovered a remarkable amount of new information about how light spectrum affects plants and especially how it affects cannabis plants. They have used this information to develop custom LED grow lights that produce better yields and bud quality with cannabis than other grow lights, and even overall better bud quality than buds grown in the sun.

How do you take advantage of that power, which is only recently available to home marijuana growers? Find out today.

Quick Reference: How different colors in the light spectrum affect cannabis growth

  • Blue light – Helps keep cannabis short and healthy
  • Green light – Keep cannabis healthy and increase penetration into the plant
  • Red light – Makes cannabis grow more tall, helps with flowering
  • Far Red Light – Crucial to potency and bud formation
  • UV light – Increase trichomes and smells/terpenes

Read the full tutorial on how spectrum affects cannabis plants here.

 

Ideal Spectrum: What’s the best custom mix for LED grow lights?

The ideal spectrum for growing cannabis with LED lights is typically a wide-spectrum or full spectrum light. In other words, it contains significant amounts of blue, green, red, and far red. The light will typically appear white, or white tinged with blue/red/pink depending on the particular light. If your grow light is making “blurple” light, where the light almost looks like a black light, it means you are using old technology. These lights typically get lower yields and reduced bud potency compared to modern LED grow lights with a cannabis-friendly spectrum.

“Blurple” LED lights are old technology and should be avoided if you have the choice. They don’t grow weed as well as modern LED grow lights which contain a wider spectrum.

Note: If the leaves don’t look green under the light (for example if they look purple such as in the picture above), that means it’s an especially bad LED light. If you can’t see the green of leaves, that means there is no green in the spectrum, which is bad because green light is essential for the best growth and yields with cannabis plants. On top of not being ideal for the plants, the unnatural color makes it difficult to see whether your plants are experiencing nutrient deficiencies.

Good modern LEDs make light that appears mostly white, though often with a tinge of blue, yellow, or red/pink.

Good vegetative LEDs produce light that looks pure white or a little blue.

Good flowering LED grow lights typically have light that looks a little pink or yellow, but the plants should still appear in full color.

What else to pay attention to:

  • Form factor (shape and size) – make sure the LED is designed to fit the size space you’re growing in. A too-strong LED grow light can kill plants or overheat a small space.
  • Quality of parts – There are many aspects of an LED panel including LED diodes and drivers (Meanwell, etc.). The best way to make sure you’re getting the best technology is to choose modern LED grow lights from trustworthy manufacturers. Some of the cheap generic LEDs use hold-technology LED diodes and drivers which are less efficient. In other words, they put out less light and more heat for the amount of electricity used. Try to choose LEDs that talk about using the
  • Actual cannabis grow reports (Most important!) There are more factors going into what makes a great LED grow light than the average cannabis grower will ever care to learn. That’s why it’s often better to choose an LED light because it’s been proven to grow great cannabis as opposed to looking at the specs and trying to figure out which will be the best in theory. Just like with video games, theory-crafting doesn’t always end up how you expected when it comes to real life results.

When it comes to figuring out the best LED grow lights, pay most attention to how cannabis plants produce under them.

I grew this plant under the SF-1000 in a mini 2’x2’x4′ grow tent. Check out the grow journal here.

I grew these plants with an SF-2000 in a 2’x4′ grow tent, which produced over 10 ounces of buds. Here’s the grow journal.

The HLG 300 R-Spec really brings out the purple for many strains. Check out the full grow journal.

View my grow journals to see more examples of LEDs in action.

 

 

What are the best LED grow lights for cannabis?

You can get away with just about any LED grow light in the vegetative stage, but cannabis plants are a lot more picky in the flowering stage.

Best Vegetative LED grow lights

  • High in blue to help keep plants short
  • Often listed as…
    • “Veg”
    • “Vegetative”
    • “All-purpose”
    • “Full spectrum”
    • “4000k” or higher – This describes a particular “light color temperature” on the Kelvin (K) scale, which is another way of measuring light color. Any LED grow light with a Kelvin number from 4000k-6500k is good for the vegetative stage. 4000k or 4100k is most common.
  • You can also use flowering LED grow lights in the vegetative stage, but plants may grow more tall and stretchy

In the cannabis vegetative stage, plants only grow leaves and stems

Best Flowering LED grow lights

  • High in red and far red
    • May be listed as “Veg and Bloom”
    • Some are listed as “Bloom” or “R-spec” or Red Spectrum
  • Powerful (flowering cannabis plants want a ton of light)
  • Tested on flowering cannabis plants
  • Check out this list of recommended cannabis LED grow lights – This list is updated regularly.

It can be hard to keep track of all the new LEDs coming out, and it can also be difficult to compare them. I tried to make that easier by writing a list of recommended LEDs with pictures of them in use, estimated yields, specifications, and other helpful information.

Looking for LED grow lights that were tested on real cannabis plants? Click here.

Get the right LED grow light for the best results in the flowering stage. Cannabis needs the right kind of light for the best yields and bud potency

 

 

What else to know about LED grow lights

I hope this article about LED grow spectrum helps you get the right LEDs. Contact me and let me know what you think of the article.

~Nebula Haze

 

 

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