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Friday May 13, 2022

By Trevor Ross

cannabis plants under a grow light Education

At the Smithsonian Institution in Washington, DC, the original Star-Spangled Banner — the American flag which flew over Baltimore Harbor during the War of 1812, and which inspired Francis Scott Key to write the words to the national anthem — hangs on display in a darkened room, where no flash photography is allowed. But why shouldn’t a national treasure of such magnitude be displayed in full light, or allow visitors to take clear pictures beside it? The answer is light degradation, or the process by which light damages organic material over time. The two-hundred-year-old flag is made of cotton which, like all organic material, is susceptible to light degradation. In this regard, cotton and cannabis are no different. So will light harm your weed? In short, yes, light will begin to degrade cannabis as soon as it is cut from the plant.

This article reviews the science behind light degradation, how light affects weed, and how to properly store your cannabis to reduce THC degradation.

Light and the Electromagnetic Spectrum

To understand how light degrades THC, let’s first review precisely what light is. Light is energy, specifically electromagnetic radiation. In fact, all color we perceive represents a small visible slice of the whole electromagnetic (EM) spectrum which includes harmless radio waves all the way up to dangerous gamma radiation. At low frequencies, like radio waves, this energy is harmless, and passes through organic material with minimal effect.

image showing the frequencies from a radio wave in pink and purple
Radio waves are an example of electromagnetic radiation that we are exposed to every day. photo credit

But at higher frequencies, this energy begins to strip electrons from the atoms and molecules it passes through in a process called “ionization.” This ionizing radiation harms organic material at the atomic level by damaging organic compounds, including DNA.

Thankfully, not all electromagnetic radiation is ionized, which is why a hundred radio stations can broadcast harmlessly through us every day. The threshold for ionization is in the ultraviolet range of the EM spectrum, which is typically divided between higher and lower energy ultraviolet (UV) radiation.

Higher energy UV regularly causes radiation burns in humans that we call sunburns. During a sunburn, the rest of the complex human organism is relatively unscathed, but the outermost layer of our epidermis suffers an assault of ionizing radiation, killing many of the skin cells affected, and the surviving cells risk becoming cancerous. This is also the same process that turns grass brown and fades untreated wood. One can imagine, then, what this light does to the sensitive resin on the surface of a cannabis flower.

Light and THC Degradation

THC is not a very stable compound to begin with. Though it develops in large amounts while the plant blooms, as soon as those blooms are cut THC degrades into CBN with exposure to light, as well as air and heat.

Even when left uncut, THC eventually develops into CBD (a process some growers allow to adjust the ratio of CBD in their harvest). For growers aiming to maximize THC, or for consumers hoping to retain as much THC in their product as possible, light degradation is a serious threat.

a flowering green marijuana plant
THC will develop when the plant is in the flowering stage, but you have to be careful once the buds are harvested in order to reduce light degradation. photo credit

UV light in particular is a more serious threat than the soft watts burning from filament bulbs. However, the fluorescent lights of most retail shops emit small amounts of UV light, as well as the energy-efficient compact fluorescent lamp (CFL) bulbs which are becoming more common in homes. To be clear, brief periods beneath UV lights, like viewing, grinding, or smoking cannabis, will have little effect on the consumer’s experience. But if that cannabis has been stored long-term, especially for days or weeks beneath the fluorescent lights of the dispensary or your own fluorescent bulbs at home, then it will inevitably lose potency.

One study in 1976 tested THC degradation over two years of various storage methods and concluded that exposure to light was “the greatest single factor in loss of cannabinoids especially in solutions,” and another more recent study found that cannabis can lose up to 16% of its THC over the first year of storage. Other contributors to this degradation include temperature and oxygen.

Other Factors of THC Degradation


a woman holds a small open jar of cannabis, examining what's inside
In addition to light, oxygen can degrade your cannabis too. photo credit

Light is the primary threat to THC because high-energy light can strip electrons from organic material, damaging its atomic integrity. But oxygen can have a similar effect. Oxidizers (oxygen being the most common) are substances that cause other compounds to lose electrons, or become oxidized. Much like light exposure, oxidation contributes to the process that converts THC to CBN. In fact, some luxury cannabis companies have taken to packaging in nitrogen to slow this process while the cannabis is in transit.


Research has also found that heat plays a role in cannabinoid breakdown. Studies in the 70s determined that lower temperatures showed a slower rate of cannabinoid loss, with temperatures below freezing exhibiting the lowest rate of loss. Anything between freezing and about 70° F proved fairly stable, but temperatures above that began to degrade THC more rapidly.

Thankfully, the solution to all of this is relatively simple. Cannabis should be stored in a dark, temperate area away from any hot devices like computers or ovens, and certainly out of sunlight.

How to Properly Store Cannabis

a white opaque container with a black top
Storing your cannabis in an opaque container is a great way to prevent light degradation. photo credit

Cannabis should be stored with consideration of all these factors — light, temperature, and air. Keep flower in opaque containers whenever possible. Glass mason jars remain a great option for storing and curing weed because their rubber seals keep oxygen out, but they will let a lot of light in. Rubber sleeves are available for most sized jars, but keeping them in a drawer or cupboard works just as well, as long as those areas don’t get too warm.

Freezing is viable for long-term storage, particularly for flower destined for edibles or home extraction, but thawed flower will likely be a bit wilted and difficult to smoke. Be sure to use an air-tight container when freezing cannabis as well. Not only will this block oxygen from getting in, but it will also block moisture that could result in freezer burn, destroying the flower and THC altogether like a deep winter frost.

Frequently Asked Questions

Does Light Affect Dabs?

Yes. Light, especially ultraviolet (UV) light degrades THC over time, so cannabis flower and concentrate should be stored in a cool, dark space.

Does UV Light Affect Cannabis?

Yes. UV light is capable of degrading cannabis at the atomic level by stripping electrons from the organic molecules, damaging THC and reducing potency.

How Much Light is Best for Cannabis?

Ideally, cannabis should be stored in the dark. Small amounts of intermittent light, like opening a jar to remove some, or rolling a joint, will not have much effect on the end experience. But cannabis stored beneath light over several weeks will begin to lose potency.

What Light Do You Use For Cannabis?

Cannabis is most safely handled under low-watt filament bulbs. Cannabis is typically grown beneath sunlight or LEDs designed to mimic the sunlight of different seasons; however, after cutting, that same sunlight will accelerate the degradation of THC into CBN. Fluorescent bulbs including compact fluorescent lamp (CFL) bulbs also emit small amounts of ultraviolet (UV) light which harms THC as well.

How do you keep your cannabis safe from light degradation? Share in the comments below!

Photo Credit: Shutterstock


Trevor Ross Trevor Ross

Trevor Ross is a writer, medical marijuana patient and cannabis advocate. He holds an MFA in writing from the School of the Art Institute of Chicago. He has previously worked as a copywriter, a teacher, a bartender, and followed Seattle sports for SidelineBuzz. Originally from Washington state, you can find him now working in his garden or restoring his house in Scranton, PA, and he can be reached through LinkedIn.

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