12. Lighting


Light is an essential factor for plant growth. Greenhouses are designed to create an optimal environment for growing plants. They are transparent to sunlight, yet sufficiently enclosed to reduce convective heat loss. Because natural sunlight is the cheapest source of light available, translucency of the greenhouses and greenhouse shading are important factors. Unfortunately natural sunlight isn’t always available in sufficient quantities for commercial growing. As commercial greenhouse growing has become more advanced, the use of artificial light has become very common in greenhouses to increase production and quality. Greenhouse grow lights are increasingly applied for commercial purposes. Artificial lighting allows growers to increase their productivity and extend the growing season. The application of grow lights started with ornamental crops for off season production but is now also increasingly used for vegetable crops. For plants to grow, they use a relatively small portion of the total input (spectrum). Artificial greenhouse lighting is designed to enhance plant growth and to be as energy efficient as possible. Therefore greenhouse lighting systems deliver a different spectrum than usual light sources and are constantly innovating to optimize their energy efficiency.

Supplemental Greenhouse Lighting

For commercial greenhouse production, supplemental lighting is most beneficial in areas that receive less than 4.5 hours average daily sunshine. In many greenhouse growing regions this occurs in winter as a result of the combination of high northern or southern latitudes and overcast weather. By ‘supplementing’ artificial light to the natural daylight, growers can significantly extend growing seasons and dramatically increase crop production.

Replacement Greenhouse Lighting

Because sunlight is a free input, it is usually best to take maximum advantage of the solar conditions. Seldom has it been shown that 100% artificial lighting is economically feasible for commercial greenhouse crops. For propagation purposes however, replacement greenhouse lighting can be a useful method.

Even though it is highly variable, sunlight is far more intense than any commercially practical artificial sources and it is has a broader, fuller spectrum of photo synthetically active wavelengths. When constructing growing environments where the total lighting is from artificial sources, it is normal to mix grow lights types to achieve a more balanced spectrum, and many configurations have been devised and studied. However, there remain practical difficulties in achieving a uniform distribution of light when using grow lights.