The Effect of Grow Light Leaks in Sealed Grow Rooms

When setting up an indoor gardening operation, growers spend exorbitant time and money in the creation of environments where plant species thrive. For sealed grow room design, 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. Many of these challenges are relatively non-existent in the natural world. The reaction of indoor crops and cannabis plants to “grow light leaks” during dark periods (nighttime) presents one of these rather unusual phenomena.

Certain species of plants are subject “photoperiodism.” With these species, varying light cycles between day and night cause plants to enter new phases of growth. To illustrate, uninterrupted 12-hour periods of darkness (nighttime) causes cannabis to start flowering. This process occurs as a hormone named “photochrome” reacts to sunlight intensity and durations. Next, photocrome directs plants towards different phases of growth. If a sealed grow room is not 100% dark during the nighttime period, cycles of photoperiodism can be interrupted. This causes photochrome imbalances as related to specific plant processes like cannabis. 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 CEA and cannabis cultivation operations, here are some points of wisdom in dialing horticultural lighting:

Grow light leaks

Grow Light Leaks and Inconsistencies and Stress

Growers should always strive for consistency concerning grow room design. Because, most crops like cannabis perform at their best in stable environments. Consequently, bountiful harvests are the result of constant environmental balances during both vegetative growth and flowering. This notion includes stable lighting intervals.

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. A such things like nutrient uptake can be affected and eventually retard growth.

Light leaks can also prove troublesome regarding photochrome levels in plants. 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. This notion is explicit in cannabis cultivation.

Grow Light Leaks and Hermaphrodites

One of the most widely known negative side-effects of horticultural lighting seepage has to do with the changing of female plants into hermaphrodites. Hermaphrodites can prove devastating for a crop. This notion is especially true for those looking to grow seed-free flowering plant varietals. Because, male flowers on a single plant can pollinate an entire grow room.

Expert growers agree that certain plant species turn hermaphrodite as a result of environmental stressors. In cannabis cultivation, light leaks being notorious 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.” Still, indoor growers should strive to avoid any disruptions in regular light cycles. Either way, it takes rather consistent light exposure on a plant to force it into hermaphrodite growth. These sorts of leaks come from constant sources. Examples of these sources would be under doorways and walls, which occur consistently on a day-to-day basis.

Grow Light Leaks Mean “Other Leaks”

Indoor growers can be assured that if their sealed grow room 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. For this process, primary concerns are atmosphere, temperature, and sterility. All of these contingencies are compromised with an improperly sealed grow room.

If leakage issues arise, growers sacrifice the total environmental control that is so essential in sealed room horticulture. With this issue comes potential problems with maintaining ideal, static levels of temperature, humidity, and CO2. Moreover, sealed rooms are wholly dependent upon CO2 injection technology. Unfortunately, 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, its is virtually impossible to fully sterilize a leaking indoor garden. Because, bugs and spores (of powdery mildew and botrytis) can continuously access the grow space via leaks.

Locating Grow Light Leaks

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

To inspect an indoor garden for horticultural lighting leaks, its best to enter the grow with a green light when the primary lights are off. Once situated in the garden, one should turn off the green light and sit still for a while to let one’s 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 trouble with light leaks. Also, this inspection process should be done during various parts of the day. Because, 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 put off light. More often than not, this light is colored red or green and is residual from the digital readout on said equipment. 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 grow rooms 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 cannabis cultivation and CEA opertaions.

This article originally appeared in the January 2019 edition of Maximum Yield Magazine.