What is Light Deprivation?

When do you need a light deprivation greenhouse?

Light deprivation (light dep) is a cultivation technique that takes advantage of a plant's photoperiodism capabilities, tricking it into flowering sooner than the natural cycle. This is accomplished by simulating the day and night cycles of late summer months with photoperiods of 12-hour light and 12-hour dark. Plants flower, bloom, and bear fruit at an accelerated rate providing more abundant and frequent yields. If you are looking to buy a light deprivation greenhouse, Hortitech Direct offers a variety of Light Dep Greenhouse Kits that you can compare!

Light Dep Greenhouse Overview

Light Deprivation Greenhouse Overview

To set up a light deprivation greenhouse, it is best to create your light dep systems at the time you are designing the greenhouse. It is possible to get light dep retrofit kits, but it makes sense to invest in a light dep system upfront if you are already building a new greenhouse.

It is also important to remember that using light deprivation plastics significantly changes the climate in your greenhouse. Having good ventilation to prevent crops from overheating and getting mold is very important.

When it comes to operating a light dep greenhouse, attention to detail pays off. The more precision control and consistent timing you have, the better the crops will yield.

What is Photoperiodism?

Some plants rely on cues from nature to tell them when it is time to move into the next growth stage. These are long-day plants and short-day plants. Long-day plants include many types of lettuce.

Controlling Photoperiods: Daylength and Timing

Photoperiod control can reduce cropping time because you do not need to wait for the seasons to change and give plants cues to mature. Instead, you can use light deprivation systems to trick them into thinking the season is ending sooner than it actually is. Timing is everything when it comes to light deprivation. You will need to schedule your light dep covering to be put on and removed based on local sunrise and sunset data.
Example: If you apply light dep during cooler times of day it will help prevent heat and moisture build-up. For a 12 hour cycle you may choose to take blackout cloth off at 8am and apply it at 8pm to trigger flowering.
Naturally, the amount of time between sunrise and sunset varies seasonally and based on latitude. Day length can be calculated based on sunrise and sunset times for a given latitude with civil twilight time added. 

The maximum intensity of moonlight is only 0.02 ft-c so the light from the moon will not have enough intensity to trigger flowering and is not of concern. Persistent fog or cloudiness is a concern and can shorten the perceived day length in photoperiod sensitive plants. In those situations, supplemental lighting or daylight extension lighting may be needed.

High-Level Light Dep Planning

Civil twilight is something to consider when dealing with calculating sunrise and sunset because that additional light may throw off your 12/12 hour light cycle. Taking civil-twilight into consideration with your light dep cycles will help you perfect your light dep schedule. The civil twilight time interval must be added to sunrise and sunset time when calculating day length to control flowering of short-day plants because even this very low intensity of light can trigger flowering. 

Example: Sunrise at 6am and sunset at 8pm would give 14 hours of light, if the sun will be in civil twilight for 15 minutes, twice per day, that would equal 14 hours and 30 minutes of daylength. Civil twilight is estimated by some as an additional 30-40 minutes of light.
Civil twilight is the time interval between sunrise or sunset, and the time when the sun is 6° below the horizon. In each 24 hour day, there are two civil twilights, one before sunrise, and one after sunset. Civil twilight is a time when the sun reaches very low intensities around 2 footcandles (ft-c). At sunrise and sunset, the sun’s intensity can be as much as 10 times that.
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