light deprivation greenhouse inside view

Advantages of Exterior Light Deprivation Systems Over Interior

Light deprivation systems are an important component of many greenhouse setups. Plant growth and flowering cycles are strongly influenced by seasonal light levels, and greenhouse growers have perfected techniques for manipulating those natural cycles through the use of artificial UV lighting and artificial light deprivation.

Most light deprivation systems take the form of a sheet of opaque material that covers the transparent walls and roof of a greenhouse, thus blocking out sunlight and UV rays and creating a dark environment for the plants inside. As the names would suggest, an interior light deprivation system is affixed to the inside of the greenhouse walls, while an exterior system is externally attached. 

There are many crops that can benefit from cycles of artificial light deprivation. Marijuana plants, for example, grow rapidly during the summer months when they are exposed to long hours of strong sunlight. Then, as the days begin to shorten at the onset of fall, the plants begin to flower and produce harvestable crops. Relying on natural seasonal light cycles might mean that a marijuana grower can only harvest one good crop in a year. If a grower manages several large greenhouses, it can also be a costly, labour-intensive operation to harvest all those plants at once. And at the end of that harvest boom, the grower is left with very little supplemental income for the remainder of the year. 

With a combination of artificial UV lighting and light deprivation systems, plants can be coaxed into producing harvest-ready crops several times a year. This gives farmers and growers the ability to stagger greenhouse growth timelines and reap 3-4 manageable harvests each year, creating a more stable source of income and avoiding the need to hire large numbers of temporary workers. 

Both interior and exterior light deprivation systems can provide this benefit, however, exterior light deprivation systems offer several benefits over interior ones.


It goes without saying that if you have to affix a system to the inside of a greenhouse, you lose some interior growing space. With interior light deprivation systems, the space lost due to the bulk of the material needed to block light from entering can be significant. Hanging what is essentially a heavy curtain on the inside of your greenhouse walls cuts off a large chunk of space.

Loss of workable space with an interior light deprivation system can mean fewer crops. In a personal greenhouse this may not be too much of an issue, but with a commercial operation, the space for those few extra plants can be crucial for meeting demand and maintaining a steady income stream.  

Exterior light deprivation systems are affixed to the outside of a greenhouse structure, so there’s no impact on interior space. Plants and workable space are unaffected. 

Less Expensive

Exterior light deprivation systems tend to be cheaper — this is largely because they don’t require extra fans. Since the opaque fabric is rolled over the outside of the greenhouse, there is minimal impact to existing ventilation and interior humidity levels. 

Interior light deprivation systems tend to create a pocket of space between them and the walls of the greenhouse. Because this pocket is still exposed to light coming in through the transparent greenhouse walls, it can heat up and cause a buildup of excess condensation, necessitating additional fans and ventilation equipment to combat the unwanted heat and moisture.

Greenhouse ventilation fans can cost thousands of dollars, and greenhouses using interior light deprivation systems will often require several additional fans on top of what would normally be used — in fact, interior light deprivation setups can double or even triple the amount of mechanical ventilation required in the greenhouse. And this is often an ongoing cost, since fans have a limited warranty. Many last less than 5 years before they need to be repaired or replaced, depending on the interior greenhouse conditions. 

On top of the cost of buying and installing extra fans, all the extra ventilation contributes to energy bills. Being able to ventilate a greenhouse properly without the need for extra fans running all day and night saves money and allows for more space and a more comfortable working environment for growers and harvesters. 

Allows for Easier Maintenance of the Greenhouse Environment

Clear-walled greenhouses are meant to let UV rays and sunlight in, trapping heat inside. When sunlight entering a greenhouse hits the blackout material of an interior light deprivation system, a warm, humid microclimate is created in that space, which encourages condensation to form. Extra condensation means a more humid environment inside the greenhouse.

For a variety of crops, and especially for cannabis, humidity levels are an important determiner in a crop’s overall success. Light deprivation is a great tool for increasing crop yields, but too much moisture can lead to mold and other issues, which can mean lost crops and lost profits. An overly humid greenhouse environment can also be detrimental for greenhouse workers who are spending long hours in that space. 

An exterior light deprivation system offers complete coverage from sunlight, with minimal interference to the interior environment of a greenhouse. If it’s employed correctly there should be no need for extra ventilation beyond what the greenhouse already uses.  

While both interior and exterior light deprivation systems are great ways to increase crop yields, there are clear advantages to using an exterior light deprivation system. Exterior systems can save space, energy, and money, and are the best option for minimizing disturbances to the plants and the environment inside the greenhouse.