Kent Gruetzmacher | January 4, 2019

Takeaway: Light leaks in your sealed growroom can be disastrous for some kinds of plants. They can also be a sign that more than just light is getting in, including pests and other environmental variables.

When planning and setting up indoor gardens, growers spend time and money in the creation of environments where plant species thrive. For sealed growrooms, this process represents a careful balancing act between temperature, humidity, light, and CO2. However, once an indoor grow is operational, these synthetic environments create challenges for growers that are non-existent in the natural world. The reaction of indoor plants to light leaks during dark periods (nighttime) presents one of these unusual phenomena.

Certain species of plants are subject to photoperiodism, in which the varying duration of light cycles between day and night cause plants to enter new phases of growth. To illustrate, uninterrupted 12-hour periods of darkness (nighttime) causes some plant species to start flowering. This process occurs when a hormone called photochrome reacts to sunlight intensity and durations, directing plants towards the different phases of growth.

If a sealed growroom is not 100 percent dark during the nighttime period, photoperiodism cycles can be interrupted, causing photochrome imbalances as related to specific plant processes. These hormonal imbalances can have negative and sometimes detrimental effects on an indoor harvest.

For those looking to avoid issues with light leaks in their sealed growrooms, consider the following points.

Inconsistencies and Stress

Indoor gardeners should always strive for consistency in their growroom environments. Most crops perform best in stable environments, and bountiful harvests are the result of constant environmental balance—including stable lighting intervals—during both vegetative growth and flowering. A common misconception amongst indoor growers is that light leaks during the vegetative growth phase won’t disrupt crop growth. However, any irregularities in lighting patterns can stress plants out. Along this line of thought, all environmental stressors inhibit essential plant functions, such as nutrient uptake, and retard growth.

Light leaks can also prove troublesome regarding photochrome levels in plants, as unexpected or irregular doses of light can alter stable hormonal conversion processes. During flowering phases, excess light during dark periods can push photochrome activity to the point of converting a plant back into vegetative growth.

(Check out Three Considerations to Make When Designing Growroom Lighting.)

Hermaphrodites

One of the most widely known negative side effects of growroom light seepage has to do with the transformation of female plants into hermaphrodites. For those looking to grow seed-free flowering plant varietals, hermaphrodites can prove devastating for a crop. This is because male flowers on a single plant can pollinate an entire growroom and greatly devalue a harvest.

Expert horticulturists agree that certain plant species turn hermaphrodite as a result of environmental stressors, and light leaks are notorious for being associated with this phenomenon. However, it should be noted that the occasional beam of light on a garden from a headlamp won’t cause plants to “herm.” While indoor growers should strive to avoid any disruptions in regular light cycles, it takes rather consistent light exposure to force a plant into hermaphrodite growth. These sorts of leaks come from constant sources, such as under doorways and walls, that occur on a daily basis.

Light Leaks Mean Other Leaks

Indoor growers can be assured that if their sealed growroom is leaking light, it has issues with other leaks. Seasoned cultivators go to great lengths to ensure that their sealed gardens are functioning at their best when it comes to atmosphere, temperature, and sterility. All these contingencies are compromised with an improperly sealed growroom.

If leakage issues arise, growers, sacrifice the total environmental control that is so essential in sealed room growing. With this issue comes potential problems with maintaining ideal, static levels of temperature, humidity, and CO2. Moreover, as sealed rooms are wholly dependent upon CO2 injection technology, the regular loss of CO2 to leaks is financially burdensome and operationally threatening.

If light leaks can penetrate the confines of a sealed garden, so can airborne pathogens. As such, it is virtually impossible to fully sterilize an indoor grow if bugs and spores (of powdery mildew and botrytis) can continuously access the grow space via leaks.

Locating Light Leaks

Many indoor growers don’t know that their rooms have light leaks until it is too late, and the problem expresses itself by way of hermaphrodites and seeded flowers. As a result, it’s a good idea for cultivators to regularly check their growrooms to make sure they are 100 percent dark during the nighttime period.

To inspect an indoor garden for light leaks, it’s best to enter the grow with a green light when the primary lights are off. Once situated in the garden, turn off the green light and sit still for a while to let your eyes adjust to the blackness. At this point, it should be easy to canvass the walls and ceilings of the room and discern any potential points of light leak trouble. Also, this inspection process should be done during various parts of the day, as different angles of sunlight outside can cause light leaks during isolated time frames.

Gardeners should also be advised that control panels on grow equipment, such as atmospheric controllers and AC units, often give off light. This light is usually red or green and is residual from the digital readout. As such, it is recommended that growers cover up these light sources with electrical tape or some sort of removable opaque material.

Compared to any other form of controlled environment agriculture, sealed room growing provides the most mastery over environmental factors. However, these growrooms present novel challenges of their own, as seen with the issues surrounding light leaks. For the conscientious gardener, regular inspections of one’s garden should alleviate any light leak problems. All things considered, this knowledge will provide a better platform for troubleshooting on the macro-level moving forward.

(For info on new lighting technologies, check out You Light Up My Leaf: New Lighting Technologies for Growrooms.)

Written by Kent Gruetzmacher

Kent Gruetzmacher is a California-based freelance writer and the west coast director of business development at Mac & Fulton Executive Search and Consulting, an employment recruiting firm dedicated to the indoor gardening and hydroponics industries. He is interested in utilizing his Master of Arts in humanities to explore the many cultural and business facets of this emerging industry by way of his entrepreneurial projects.

Full Bio