Light in the greenhouse: quality or quantity?

The advantages of diffuse glass are well known to most growers: more light distribution and a more uniform horizontal light distribution. This reduces the shadow effect in the greenhouse and ensures a more even climate. Also, the light penetrates deeper into the crop, resulting in more photosynthesis. "Ten percent more haze (light distribution) usually causes one percent more production," says Ralf Derksen, Product Manager Glass at Saint-Gobain Cultilene. "At the same time, however, the rule is one percentage point more light means one percent more production. Therefore, both the quality and the quantity of light play a role in the greenhouse."

For an optimum light program, a grower should actually choose for as much diffusion as possible with the highest possible light transmission. However, the problem is that these issues do not go together: the higher the haze factor (diffusion) of glass, the higher the reflection and the lower the light transmission. Especially in winter, when the sun is low, the light transmission of diffuse glass is lower than with clear glass. "Growers must choose between diffusion and light transmission," says Derksen. "And of course, it's also possible to take a middle course, choose ‘the best of both worlds’. "There is no clear answer as to which strategy is best. The choice for a particular type of glass depends on a variety of factors : The cultivation method of a grower, the location of the greenhouse, whether or not there is assimilation lighting, the desired harvest time, etc. It is a matter of custom work."

Saint-Gobain Cultilene indicates that both its diffuse Albarino glass with AR (antireflection) coating and the extra clear flat glass with double AR coating is popular with growers. The special hydrophilic AR coating of Saint-Gobain Cultilene provides a few percent more light transmission under wet conditions. "We also see an increasing demand for our extra clear and low-iron flat-glass with double AR coating, a unique product of Saint-Gobain Cultilene. This glass allows a lot of PAR and UV light to pass through. With UV light, you just get ten percent advantage compared to diffuse glass with double AR coating. More and more growers see this added value: so far we have realized projects, among others, in lettuce, tomato and strawberry cultivation."

Derksen emphasizes that it is also important that growers take the durability of the glass they choose into consideration. "Saint-Gobain can guarantee this durability because of its unique anti-reflection treatment. During the curing process, a chemical reaction occurs between the AR coating and the glass, making it an even uniform product, which reduces sticking of dirt to the glass and warrants light transmission for many years. High light transmittance at the time of purchase is beautiful, but after ten years it still must be excellent. In short, the choice for Saint-Gobain glass is a sustainable and future-proof choice."