Led Technology in Greenhouse Lighting


Light is as important to plants as it is to humans. If we go back to our basic high school education, let’s talk briefly about the photosynthesis process that provides the development of plants. In the simplest terms, photosynthesis is the chemical event that enables green leafed plants to make organic food with the sun’s rays. When plants do this, they absorb carbon dioxide and produce oxygen instead. Only organisms carrying chlorophyll can perform photosynthesis, and plants need sunlight to do this. However, today there are many light sources such as fluorescent lamps, halogen lamps, high-pressure sodium lamps and new LED lamps that enable plants to perform photosynthesis. The common feature of these light sources is that they give light between 400-760 millimicrons with wavelengths required for photosynthesis.

I think that since you are reading this article, you are in the lighting industry and you know very well how important definitions such as the number of lumens, efficacy, lux, CRI for a light source are when evaluating quality and performance. However, none of these definitions are important for the light source needed in greenhouse lighting.

In greenhouse lighting, there are 4 important characteristics in the light source:  Photosynthetic Active Radiation (PAR), Photosynthetic Photon Flux (PPF), Photosynthetic Photon Flux Density (PPFD) and photon efficiency.

Photosynthetic Active Radiation (PAR): Defines the light spectrum that plants need for photosynthesis. The wavelength is in the range of 400-700 nm. Like the perception of the human eye, there are certain wavelengths to which plants are more sensitive. These are typically found in blue-red colored spectra.

Photosynthetic Photon Flux (PPF): It is the total number of photons produced by the light source per second in the PAR range. Its unit is micromole/second (μmol/s). Similar to lumens, PPF does not show the amount of photons reaching plants. This is a good indicator of the efficiency of the light source.

Photosynthetic Photon Flux Density (PPFD): Indicates the density of active photons falling on the surface of the plant in the PAR range. It is measured in micromoles per square meter per second. Its unit is μmol/m2/s.

Photon Efficiency: It shows how many photons the light source produces per electrical energy. Explain the efficiency of the light source. Its unit is μmol / W.

Although High Pressure Sodium Lamps (HPS) are widely used in traditional greenhouse lighting today, with the rapid development of LED technology, the use of LED light source as a photosynthetic light source instead of HPS lamps is increasing rapidly. As the main reasons for this increase, LED sources have significant advantages over traditional lighting sources:

Higher yields
Long lasting
It can be adjusted to give light in the highest spectrum, specially for plant types and sizes (Traditional lighting sources give light in a fixed spectrum)
Low maintenance costs
Luminaire design flexibility (It can be applied to many luminaire designs as it emits less heat and due to its design)