LED Technology in Greenhouse Lighting

LED Technology in Greenhouse Lighting

 Light is as important for plants as it is for humans. If we go back to our basic high school education, let’s briefly talk about the photosynthesis process that enables plant growth. Photosynthesis, in the simplest terms, is the chemical process that allows green-leaved plants to produce organic nutrients using sunlight. While performing this process, plants absorb carbon dioxide and produce oxygen instead. Only living organisms that contain chlorophyll can carry out photosynthesis, and to do this they need sunlight. However, today there are many light sources that can enable plants to perform photosynthesis, such as fluorescent lamps, halogen lamps, high-pressure sodium lamps, and new LED lamps. The common feature of these light sources is that they emit light within the wavelength range of 400–760 millimicrons, which is required for the photosynthesis process.Since you are reading this article, I assume you are in the lighting industry and that you know very well how important definitions such as lumen count, efficacy, lux, and CRI are when evaluating quality and performance for a light source. However, none of these definitions are important for the light source needed in greenhouse lighting.In greenhouse lighting, there are 4 important characteristics that must be considered in a 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 in order to carry out photosynthesis. Its wavelength range is 400–700 nm. Just like the human eye’s perception, plants also have certain wavelengths to which they are more sensitive. These are typically found in the blue-red color spectra.Photosynthetic Photon Flux (PPF): The total number of photons produced per second by the light source within the PAR range. Its unit is micromoles per second (μmol/s). Similar to lumens, PPF does not indicate the amount of photons that actually reach the plants. It 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 within the PAR range. It is measured in micromoles per square meter per second. Its unit is μmol/m2/s.Photon Efficiency: Indicates how many photons the light source produces per unit of electrical energy. It describes the efficiency of the light source. Its unit is μmol/W.Although High Pressure Sodium Lamps (HPS) are commonly used in today’s conventional greenhouse lighting, the use of LED light sources as photosynthetic light sources in place of HPS lamps is rapidly increasing with the fast development of LED technology. The main reasons for this increase are the significant advantages LED sources have over conventional lighting sources:

• Higher efficiency
• Long lifetime
• Can be adjusted to emit light at the spectrum with maximum efficiency specifically for plant types and sizes (Conventional lighting sources emit light at a fixed spectrum)
• Low maintenance costs
• Luminaire design flexibility (They emit less heat and, by design, can be applied to many luminaire designs)