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Can Blacklights Be Used for Growing Cannabis?

Growing cannabis has become a popular hobby for many people, especially with the increasing legalization of marijuana in various countries. When it comes to cannabis cultivation, proper lighting is essential for healthy growth and optimal yields. In this article, we will explore the use of blacklights for growing cannabis, the benefits and drawbacks, and whether they are a suitable choice for your cultivation needs.

What Are Blacklights?​

Blacklights, also known as ultraviolet (UV) lights, emit a specific wavelength of light that is invisible to the human eye. They are commonly used for various purposes, such as detecting counterfeit currency, enhancing the colors of fluorescent materials, and creating special lighting effects in parties and concerts. However, their potential use in cannabis cultivation is a topic of debate among growers.

The Role of Light in Cannabis Growth​

Cannabis plants, like all plants, require light to carry out photosynthesis – the process through which they convert light energy into chemical energy to fuel their growth. The quality and spectrum of light are crucial factors that influence the growth and development of cannabis plants. Different wavelengths of light correspond to different colors, and each color has a specific effect on the plant's growth.

Blue light, for example, promotes vegetative growth, while red light stimulates flowering and fruiting. Plants also utilize ultraviolet (UV) light to a certain extent. UV light is typically divided into three categories: UVA, UVB, and UVC. Among these, UVC is harmful to plants and is not recommended for cannabis cultivation.

The Effects of Blacklights on Cannabis Growth​

Blacklights primarily emit UVA light, which is a part of the ultraviolet spectrum that has minimal effects on plant growth. While UVA light can help promote the production of certain secondary metabolites, such as terpenes and flavonoids, it is not sufficient to support the overall growth and development of cannabis plants.

UVB light, on the other hand, has been shown to have a more significant impact on cannabis growth, particularly in increasing the production of THC – the primary psychoactive compound found in marijuana. However, blacklights do not produce enough UVB light to make a noticeable difference in THC levels.

Drawbacks of Using Blacklights for Cannabis Cultivation​

There are a few cons to using blacklights for growing cannabis:

  1. Insufficient light spectrum: Blacklights do not provide a comprehensive light spectrum required for optimal cannabis growth. They lack the necessary blue and red light wavelengths, which are crucial for vegetative growth and flowering, respectively.
  2. Decreased yields: Due to the insufficient light spectrum provided by blacklights, cannabis plants grown under them may have lower yields compared to those grown under full-spectrum grow lights.
  3. Increased electricity costs: Blacklights are generally less energy-efficient than modern LED grow lights, which means higher electricity costs for growers.

Alternatives to Blacklights​

Given the drawbacks of using blacklights for cannabis cultivation, it is advisable to consider alternative lighting sources that provide a more suitable light spectrum for the plant's growth. Some popular options include:

  • LED grow lights: These are energy-efficient and can provide a full spectrum of light, making them ideal for all stages of cannabis growth.
  • High-Intensity Discharge (HID) lights: These lights, such as Metal Halide (MH) and High-Pressure Sodium (HPS) lamps, have long been popular among cannabis growers due to their high light output and broad spectrum.


While blacklights do have some potential benefits in promoting the production of certain secondary metabolites in cannabis plants, they are not sufficient for supporting overall growth and development. Their lack of a comprehensive light spectrum, decreased yields, and increased electricity costs make them an unsuitable choice for cannabis cultivation. Instead, growers should consider investing in full-spectrum LED grow lights or HID lights to ensure optimal growth and yields.
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