Is A Black light For Growing Weed Worth a Try?

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    Are Black Lights Good For Growing Weed?

    Blacklights or UV lights are somewhat controversial in the cannabis community. Some growers believe that using a black light will result in stronger weed. On the other hand, skeptics stated that there is not any scientific proof that it actually does increases weed’s strength.

    Because the cannabis plant is illegal federally in the US, there have been very few studies on its cultivation. UV light’s effect on cannabis cultivation isn’t an exception to this problem.

    Recent studies though have indicated that the UV wavelength can help increase weed’s potency, and also provide other benefits too in an indoor garden.

    So, the question that needs to be asked is:

    Is using blacklights for soil or a hydroponic grow space recommended, for your indoor garden or should you just stick to led grow lights, HPS lights, the HID light or even a fluorescent light?

    Black Light Vs. UV Lights

    Black Lights are the same as ultraviolet light. For variety, UV and black lights will be used interchangeably throughout this article.

    Many people think that all UV light spectrums are the same, which is not correct. Therefore, they do not differentiate UVA, UVB, or UVC rays. Because of this, you should assume, in this post, unless state otherwise, that any ultraviolet light spectrum is a black light.

    Safety Precautions When Dealing With The UVA Light, a The UV B Light

    Too much UV exposure can cause skin cancer and damage your eyes. So, if you decide to use a UV light in your grow room be sure to limit exposure and also wear protective goggles designed for the UV light bulb.

    Apollo Horticulture Grow Light Glasses Goggles for Wear Fit Over Glasses for LED Grow Light Room UV400 Grow Room Safety Protective Eyewear for Intense LED Lighting Visual Eye Protection
    Grow Light Goggles

    Black Lights, (“UV Lights Background”)

    In previous posts, I’ve explained the UV grow lights’ role in the light spectrum. So, I will only briefly go over the UV electromagnetic spectrum.

    UV is short for ultraviolet light, and there are three forms of UV electromagnetic waves:

    • UV-A
    • UV-B
    • UV-C

    UVA and UV B light reach the earth, and both can cause skin cancer and damage plants. However, as long as it isn’t overdone, UV can make cannabis stronger and provide other benefits.

    UV-C emits UV radiation, which is damaging to all life forms. You do not worry about UV radiation though because of the earth’s protective ozone layer shielding effect.

    The following video, by NASA, is an excellent overview of the UV light spectrum.

    Are UV Lights Mandatory for Growing Weed?

    A UV light is called supplementary for a reason, in that they are designed to complement other grow lights and will not work on their own in growing weed indoors. So, UV lights are not mandatory as you can grow perfectly normal and excellent crops without UV lights.

    As stated earlier, UVA and UVB light historically had never been scientifically proven to help increase THC levels. Now, with the increasing acceptance of weed, there have now been recent scientific studies showing that UV rays can, in fact, help increase weed’s THC percentage. I will get to this later. But, I would first like to go into the history of UV lights and weed.

    How Was UV Lighting for Weed Discovered?

    Historically, before cannabis became commercialized, the highest THC content in weed strains came from countries that were in the highest elevations, and the higher the elevation, the more UV rays reach the earth.

    The pioneers of medical cannabis theorized that using black lights would result in stronger crops, which was followed by an experiment by testing UV supplemental grow lights on a cannabis plant.

    Their experiment resulted in the black lights substantially raising the THC level. In fact, growers who use UV lighting have reached up to 30% more THC than when a black light was not used.

    These findings although promising were, as cannabis was nearly impossible to study, not scientifically proven. However, with weeds increasing acceptance, cannabis is now being studied by research institutions and even universities.

    One such study, from Maryland, has shown that UVB on average will help increase the levels to around 28%. There also have been studies that indicated that UVA lighting will also increase THC levels.

    Does UV Help With CBD?

    Unfortunately, No. At least according to the Maryland study, which stated that UV lights did not show any increase in CBD levels.

    In Theory, How Does UV Lighting Make Weed Stronger?

    UV rays, as they damage the human skin, they also damage a growing plant. Human skin, hit by UV sunrays, as a form of self-protection, forms a tan. Likewise, cannabis when hit by UV rays, as a self-defense mechanism starts to produce more trichomes, and an additional trichome mean a higher THC percentage.

    Can You Grow Weed With A Black Light?

    UV lights have been shown to be not just promising when it comes to raising the THC percentage. Studies have also shown that a black light can help with the following :

    • CBD -Increase CBD levels. This though at least by the Maryland study, has not been scientifically proven.
    • Quality -Enhances the taste and smell.
    • Plant Growth-Helps weed develops more branches and has less stretching.
    • Resistance -Shown to be more resistant to insects, and various other pests.
    • Moldy Weed-UVB lighting has been shown to help eradicate mold spores. According to California Light Works, black lights work best during the early stated of powdery mildew and should be used during the night.

    Best Practices for Growing With Black Lights

    If you decide to use a black light, you need to remember that UV lights can also be dangerous. A trichome is cannabis‘s natural means of self-defense from UV light rays. More trichomes mean stronger weed.

    Cannabis though obviously can only take so much abuse as UV rays still damage plants. This means that UV rays can be overdone and damage your prized crops’ beyond repair. So, you need to make sure that blacklights are intelligently used, and that you take care of the information below.

    When Should You Use Your UV Light?

    Based upon a 1987 scientific study; UVA light (UV lights only for the vegetative do make sense as it is the closest to visible light in the UV wavelength)should be used by the indoor grower, only for the vegetative stage of plant growth. This same study stated that UV B light should be used only in the flowering stage.


    There is though a bit of controversy on whether or not a UVA light will help with the flowering stage. A reputable, LED light manufacturer, Black Dog, states that the 1987 study was done incorrectly and that the UV A light should work well in the flowering stage. However, many growers swear that only the UVB light used during the last two weeks of the flowering stage will help increase the cannabis THC levels.

    I am not a scientist. However, as Black Dog lights are trying to sell their UV lights, I feel that their conclusions may be biased.

    What Type of Black Light Should I Use?

    There is quite a bit of mixed information on what types of black lighting are appropriate. For example, a few reputable authorities state that you do not need to purchase a fancy, UV grow lights. They go on to elaborate that simple UV reptile lights will do just fine.

    However, others state that not just any UV light spectrum will do and that their specific black light is designed to give you the best results.

    Of course, grow light manufacturers recommend specialized and expensive black lights. So, I am skeptical when it comes to their advice. And, the one that recommended a plain lizard lamp is the highly respected Royal Queen Seeds. As a result, if your current lights do not feature UV, a reptile light should be sufficient.

    All In One Option

    Black lights are commonly included with both high-end and lower-priced full spectrum LED grow lights kits. For example, KIND LED that are considered among the best has built-in UV lights.

    Kind LED K3 Series 2 XL300 LED Grow Light for Indoor Plants and Flowers - 210w with Full Spectrum and 3 Year Warranty

    Cheaper LED grow lights have, built-in, UV. So, you should consider buying a LED system that already has black lights.

    75W LED Grow Light for Indoor Plants Growing Lamp 225 LEDs UV IR Red Blue Full Spectrum Plant Lights Bulb Panel for Hydroponics Greenhouse Seedling Veg and Flower by Venoya

                                 This Cheap LED Grow Light Has UV Capabilities

    UVB Lighting Systems

    You also may want to consider buying a separate UVB grow light system. California Lightworks is a prime example of one and is shown below.

    This one costs more than most lower-priced LED lights. So, I would spend your money first on a top, LED, grow light, and grow tent first.

    Final Thoughts

    Based upon the recent studies and also its proven track record blacklights can help you grow stronger weed. However, using a black light for growing weed, when it is done wrong can also damage your crops.

    New cannabis growers need to keep it simple when they are just starting out. Learn how to properly use a grow tent and set up your grow room first. Then grow a few crops before you add black lights. But, for those that are experienced, I would definitely give them a try.


    Can you use UV light to grow plants?

    What color light is best for vegetative growth?

    Is UV light bad for plants?

    Can you leave a black light on all night?


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