November 2, 2020

Can You Grow Weed With A Black Light? – Tested Results

Growing your own cannabis is a great way to get your own personal stash of bud, but it does take the knowledge and cannabis equipment to get a successful grow. If you’re attempting to grow indoors, then the absolutely most important piece of equipment, is the light you’ll use.

Cannabis lighting is a necessity because the sun is the driving factor of growth for cannabis plants, but if you’re inside then obviously the plant won’t be receiving sunlight fro growth, so you need a specialty light to recreate the sun.

Lighting for cannabis come in three main types of grow lights:

  • LED Lights
  • HID Lights
  • Fluorescent Lights

That being said, a common myth I’ve often heard is, “can you grow weed with a black light?”.

In this article, I decided to put this myth to the test, and went through a thorough grow process to test if black lights would provide the necessary growth.

Can You Grow Weed With A Black Light?

Short answer: No. You can’t grow weed with a black light. Black lights fundamentally don’t have the same sunlight properties (AKA they don’t have the light spectrum of light) that LED and other grow lights have.

1. Black Lights Don’t Have The Right Light Spectrum to Grow Plants:

The reason we use grow lights for indoor cannabis grows is to mimic the natural sunlight that causes the plants to grow naturally outdoors. This is traditionally found in blue and red spectrum light wavelengths, which actually causes the growth hormones to happen in cannabis and other plants.

can you grow weed with a black light?

The blue spectrum of the light encourages a plant to transition in photosynthesis which the plant will then use the light and transform it into nutrients to grow. Without enough blue spectrum light, photosynthesis will never happen.

Furthermore, when the cannabis plant gets into the flowering phase, they need red spectrum light. The red spectrum light helps to promote the growth of larger buds and flowers and without enough of it, your grow won’t flower any or enough buds. That being said, check out our guide on how to get bigger buds during flowering indoors!

To put it simply, black lights don’t emit high enough amounts of either blue or red spectrum light to trigger the growth hormone. They emit small amounts but simply not enough.

2. Black Lights Overheat and Aren’t Meant to Be Run Long Term:

Furthermore, when you’re using a grow light, they are usually on for hours at a time to mimic a natural sunlight cycle. The problem with black lights is that they are really only designed to be on for a few minutes at a time, and can overheat extremely easily if run for long periods of time. Since it takes a while to grow marijuana, you won’t want to me using a black light for weeks at a time.

This could lead to a fire (especially if you’re growing weed in your closet) or even make your grow room too warm for cannabis to grow and could kill your plants.

3. Black Lights Aren’t Bright Enough:

Similar to the light spectrum we mentioned earlier, when you’re using a light to mimic the sun, it needs to be bright enough that it actually reaches the plant in enough amounts that they can be absorbed.

That being said, black lights don’t emit enough lumens to actually travel to the plant and be absorbed (even if they did emit the correct light spectrum).

What Grow Lights Should I Use?:

If you’re looking for the best lights for a grow, then to put it simply you need to check out the VIPARSPECTRA 600W LED Grow Light.

You” definitely want to use an LED grow light if possible. LEDs are superior to other types of grow lights because they are much more cost and energy efficient as well as being designed specifically for indoor grows.

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Jacob is the owner and lead author here at  He's been involved in the cannabis growing industry since 2012.  Based outside of Denver, Colorado, his passion involves sharing his knowledge of growing and the cannabis industry.

Jacob Hydra

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