Light in the greenhouse: quality or quantity?

In recent years, there has been a lot of attention on diffused glass. Diffused glass gives better light distribution through the greenhouse, with deeper penetration into the crop. Also, Cultilene has noticed a growing interest in extra clear glass with a double AR coating that gives a considerable increase in light transmission. Whether a grower favours diffusion or light transmission depends on various factors, including cultivation strategy, location and marketing period, among others.

Most growers are familiar with the advantages of diffused glass: more light dispersion and a more uniform horizontal light distribution. This decreases the shadow effect in the greenhouse and gives a more even climate. The light also penetrates deeper into the crop to give more photosynthesis. 'Ten percent more haze (light dispersion) usually increases yield by one percent', says Ralf Derksen, Product Manager for Glass at Saint-Gobain Cultilene. 'At the same time, however, a rule of thumb is that one percent more light will increase yield by one percent. This means that, in the greenhouse, both the quality and quantity of light play a role.

Customised solutions
For the best possible light conditions, a grower should opt for the highest percentage of diffusion combined with the highest possible light transmission. The problem is, however, that these two factors cancel each other out: the higher the haze factor (diffusion) of glass, the higher the reflection and the lower the light transmission. Particularly during winter months, when the sun is low in the sky, the light transmission of diffused glass is inferior to that of clear glass. 'Growers therefore need to choose between diffusion and light transmission', Ralf Derksen explains. ‘Naturally, it's also possible to opt for a middle ground: the best of both worlds.' There is no single answer to the question of which strategy is best. Various factors go into choosing a certain type of glass: a grower's growing method, greenhouse location, whether or not assimilation lighting is used, desired harvesting period, etc. The right choice will always be based on a customised solution.'

Diffused and clear glass
Saint-Gobain Cultilene has noticed that both its diffused Albarino glass with AR (anti-reflection) coating and its extra clear float glass with double AR coating are liked by growers. Under wet conditions, Saint-Gobain Cultilene’s special hydrophilic AR coating increases light transmission by several percent. 'We're also seeing an increasing demand for our extra clear, low percentage iron oxide float glass with double AR coating: a unique product supplied only by Saint-Gobain Cultilene. This glass admits very high rates of PAR and UV light. With UV light, you easily increase your yield by 10 percent as compared to diffused glass with a double AR coating An increasing number of growers are becoming aware of this added value: we have now realised projects for crops such as lettuce, tomatoes and strawberries, to name but a few.

Durability
Derksen emphasises that it's equally important for growers to consider the durability of the glass they select. 'Saint-Gobain can guarantee this durability because of the unique anti-reflection treatment it provides. During the hardening process, the chemical reaction which happens between the AR coating and the glass fuses both into a single, uniform substance. Dirt collects on the glass slower, so ensuring that light transmission is safeguarded for a good number of years. High light transmission when buying your glass is great, but this quality should be maintained for at least another ten years. In short: choosing Saint-Gobain glass is not only a durable, but also a sustainable choice.'

For more information:
Saint-Gobain Cultilene
Zeusstraat 2
5048 CA Tilburg
Netherlands
t + 31 (0)13 578 00 57
info@cultilene.nl
www.cultilene.com