The rapidly expanding cannabis cultivation market has experienced many growing pains including excessive energy and water use that can cause negative environmental impacts. One little-known consequence of greenhouse marijuana cultivation, in particular, is marijuana light pollution. Greenhouse growers have many advantages over indoor and outdoor cultivation methods but also require artificial lighting systems to create a dark photoperiod.
Cannabis plants depend on a light-dark cycle to know when to switch from vegetative growth to flowering. Starting in late summer, daylight hours decrease signaling the end of the plant's life cycle and the start of the flowering period. Greenhouses that employ lighting systems at any point of a plant's life cycle can not only drive up energy bills but also disturbing neighbors and wildlife, if not properly contained.
Table of Contents
Marijuana Light Pollution
Generally, cannabis plants begin to flower when they are receiving 12 hours of daylight and 12 hours of darkness. Many other photoperiod plants also require certain daylight hours to start different life cycle stages. Some growers may opt for more hours of daylight depending on the strain. Greenhouse cultivators will use artificial lighting to compensate for the lack of sunlight through the vegetative state into the flowering stage. If there's no covering, the lights will shine out into the sky contributing to light pollution. Marijuana light pollution can end up harming the surrounding wildlife and humans, too.
According to the International Dark-Sky Association, light pollution is "the inappropriate or excessive use of artificial light." Light pollution is broken down into multiple components including glare (blinding light), skyglow (brightening of the night sky in populated areas), light trespass (bad control of lighting), and clutter (grouping of lights). The 2016 "World Atlas of Artifical Night Sky Brightness" found that 80 percent of the world's population lived under skyglow, and 99 percent in the U.S. and Europe. In terms of marijuana light pollution, light-abatement techniques are a necessity to reduce the consequences of ecosystems and humans.
The Consequences Of Marijuana Light Pollution
Marijuana light pollution can negatively affect plant life, birds, insects, and other nearby animals. Light pollution can affect nocturnal prey that are left exposed and more vulnerable to predators hunting at night. A complete ecosystem can be affected if certain prey become more scarce. One study found that frogs reduced their croaking or mating call when exposed to artificial light. Artificial light also has the power to confuse long-distance migratory birds and affect their reproductive physiology.
Marijuana light pollution also affects neighbors' circadian rhythms, the body's natural sleep/wake cycle. Sleep cycles can be dramatically affected by increased exposure to light. For example, the artificial blue light emitted from smartphones has been linked to heart disease, obesity, and diabetes. Another study on the negative effects of artificial light found that nurses who worked more rotating night shifts had a moderate increased risk in developing breast cancer.
Marijuana light pollution can sometimes be confused with a wildfire. When the cloud cover and fog is low enough, the moisture in the air can enhance the glow of the light. Wildfires are a real risk for many cannabis cultivators. Depending on the topography of the location, some neighbors may believe the glow of artificial lights is a wildfire. Distressed calls to firefighters can waste resources by pursuing a false alarm.
Marijuana Light Pollution Hits The Countryside
Marijuana light pollution from greenhouse sites is turning up more and more in rural locations, which can disrupt neighbors who enjoy looking up at the stars. Whether it's the lack of regulations or lack of knowledge about the light pollution issue, many cultivators are facing backlash from neighboring residents. Last year, Canopy Growth heard complaints from Langley, B.C. residents about the bright lights emanating from its facilities. In response, Canopy put up shades on the sides of their greenhouse facilities to reduce the light pollution.
Greenhouse growers can incorporate similar methods to reduce marijuana light pollution, but it may require a few weeks or months to install the shades or covers. Some areas don't have regulations for greenhouse cultivation, which can not only disturb neighbors, but also contribute to other negative effects on the environment including increasing energy use, damaging the ecosystem and wildlife, and harming humans. In the rural areas, the increased energy use can also increase the risk of diesel spills and wildfires from generators.
Humboldt County, for example, has regulations that state that "cultivators using artificial lighting for mixed-light cultivation shall shield greenhouses so that little to no light escapes. Light shall not escape at a level that is visible from neighboring properties between sunset and sunrise. Residents can complain to the Humboldt County Planning Division and cultivators have 10 working days to fix the light shielding issue.
How To Prevent Marijuana Light Pollution
Greenhouse growers are using blackout shields to reduce marijuana light pollution. When cannabis plants begin the 12/12 photoperiod, greenhouse growers can employ rubberized fabrics or portable awnings, for example, to contain light. Lighting curtains are helpful not only to reduce marijuana light pollution but also reflect light back to the cannabis plant. Blackout curtains increase the lighting efficiency by reducing the amount of light that goes out of the greenhouse.
Greenhouse Product News (GPN) suggests installing blackout curtains at the roof, sidewalls, and gable walls to reduce the light going out. They also suggest using roll-up screens or solid screens to avoid light pollution from coming out of the sides. Minimal gapping of the curtain can be used to reduce the humidity levels caused by the contained heat from lights.
Each municipality will have different requirements to reduce marijuana light pollution and maintain dark sky compliance. Some screens can block over 99 percent of light by using white reflective layers around a starting black layer. Lighting screens also enable greenhouse cultivators to use whatever lighting they please without concern for disrupting neighbors. Growers can make the daylight longer depending on the crop they're growing.
Issues With Blackout Curtains
The complementary use of blackout curtains and lights like high-pressure sodium (HPS) lights can generate a lot of heat. With bulbs emitting over 1,000 watts each, greenhouse cultivation sites that use blackout curtains can have an increased chance of fire damage. The distance between blackout screens and lights is vital. Depending on the type of screen used, the heated greenhouse can create a fire risk.
Cultivators recommend installing light fixtures as high as possible. GPN suggests installing the blackout curtains "as close to the bottom cord of the truss as possible to provide a flat surface to mount to." It's recommended to keep curtains between 30 to 50 cm away from the light fixture. Measuring from the ballast may still be too close and increase the chance for curtains to burn or melt. Growers can ask their screen manufacturer to determine melting points or ensure that their screens have fire retardants.
Marijuana light pollution doesn't have to cause widespread ecological damage before cultivators and regulators step in to prevent more consequences. Light pollution is not restricted to marijuana cultivation, but has gained more notice. Unlike other ecological impacts like threatening wildlife and damaging forests, marijuana light pollution has a fairly easy fix. Educating cultivators and regulators on the importance of blackout screens can reduce pollution from lights in greenhouse facilities.
