The primary way to increase the yield of a greenhouse crop is to increase the amount of photosynthetic light delivered to the plants. The amount of light that plants receive should be optimal as both excessive and deficient light can impact growth negatively. Since the natural light levels keep changing with the season, time of the day and geographic location, most of the growers depend on artificial lighting which provides the convenience of customizing the light to specific plant requirements. Artificial lighting allows growers to have controlled lighting environment inside the greenhouse. They can provide plants with only usable light (wavelengths between 400 and 700 nm – PAR radiation) and limit the amount of light provided to the plants on a daily basis. Most greenhouse growers monitor how much light their crops are receiving inside the greenhouse during a 24 hour day. This measurement of light received by the plants in a day is called Daily light integral (DLI). The measurement of DLI has many advantages in greenhouse farming as it will let the growers determine the optimal lighting requirements for their crops.

Measure of Daily Light Integral (DLI)

DLI is measured as the amount of photosynthetic active radiation (PAR) received per square meter over a 24-hour day period and is expressed as mol/m2/day. It is defined as the combination of light intensity (moles of light per square meter) and duration (per day). Technically speaking, it is the number of moles of light photons received per square meter per day. DLI is one of the useful metrics that determine growth, development and yield of the crops. The actual amount of light transmitted to the greenhouse crop is dependent on several factors like greenhouse structure, wall materials, hanging baskets etc. These factors will lessen the amount of sunlight transmitted through the greenhouse structure to be delivered to the plants. Generally, cultivators measure the DLI outside the greenhouse as well as simultaneously inside to compare the light intensities and determine the best lighting conditions for their crops. They can estimate how much light on the daily basis is being lost by greenhouse structure and what extra amount of light is required to maximize the yields. Thus, by measuring the light intensity during different times of the day in different areas of greenhouse, cultivators can determine the optimal lighting for their crops to maximize growth and production.

What happens when DLI is Not Optimized?

Plants respond differently when exposed to different light levels. Plant growth will be optimized if the correct amount of DLI is supplied to the plants as depends on the growth stage. Any excess or lack of light other than optimal can have adverse effects on plant growth. Plants grown under low DLI will have delayed growth and development. The leaves are generally yellow, stems are thin, flowers are typically smaller and fruit plants do not bloom on time.Similarly, too much light can be dangerous to the crops. It will burn and shrivel the leaves and may slow the normal plant growth.

The best way to avoid these problems is to provide the correct lighting based on the DLI values as needed by the crops. If DLI values are low, growers can consider installing supplementary lighting with LED grow lights, to increase the existing light intensity to more optimum levels.