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A Growers Climate: about diffuse light

Diffuse light is priority number one simply because there’s money to be earned with it. Growth improves under diffuse light while both greenhouse and plant temperature is lowered. According to Hugo Plaisier from Svensson, diffuse climate screens offer further advantages too. Cultivation can be lighter, and the dissemination of light is then better than using a diffuse coating or diffuse glass.

Before the emergence of the term ‘hortiscatter’ it was tricky, if not impossible, to compare diffuse percentages from glass, coatings and screens. Hortiscatter indicates how the light penetrating the material is spread from the penetration points. The Hortiscatter value lies between 0% for clear glass and 100% for material that spreads penetrating light evenly across all points. This creates greater clarity when comparing the performances of various materials used to create diffuse light in the greenhouse.

‘Diffuse screens for maximum cultivation performance, even in summer’


The old measurement method for ‘Haze’ provided an ambiguous overview of light permeability or the degree of light scatter for highly diffuse glass. ‘With high-haze glass, you rapidly approach 100% haze, even though in reality there is very little scatter’, says Gert-Jan Swinkels from Wageningen University & Research. The new measurement methods for single glass with or without (temporary or permanent) coatings and screens were recently confirmed in an updated NEN-norm. The terms ‘Haze’ or ‘F-scatter’ (the precursors to Hortiscatter) have thus been superseded. As a result of the new concept of Hortiscatter, the diffuse percentages of existing materials have been slightly reduced.

Lighter cultivation

Svensson has applauded the development of the term Hortiscatter and worked hard on its creation as it simplifies the process of comparing the diffuse percentages of various materials. It is great news for growers as diffuse light can substantially improve growing performance. This could include shorter growing periods, higher production rates, an earlier season and savings on chalk. The quality of the products also improves thanks to the use of diffuse screens. Various growers, of gerbera and roses for example, have dared to use lighter cultivation patterns, under diffuse screens, thus increasing light levels. For gerbera, for example, growers are increasingly opting for a screen percentage of 23% instead of 40%. Growers and cultivation advisers have been very enthusiastic, since the introduction of the Harmony climate screen in 2009.

Customized diffuse light

It's not only growers of cut flowers, but also pot plants who are working with higher lighting levels. A disadvantage of (temporary or permanent) coatings is that they do not distinguish between lighter and darker days or moments. Light permeability also varies, as does the degree of diffusion if the coating is not applied evenly. Diffuse glass does scatter light but is much less effective in doing so than Svensson’s screens. There are also many issues in relation to wear and tear, contamination and condensation on the diffuse glass. The biggest disadvantage regarding diffuse coatings and diffuse glass is that it always takes away light. With Harmony climate screens, diffuse light can be provided according to need. They offer protection against the sun, even with open windows, however the benefits of the sun can also be increased, for example in the morning to heat the greenhouse in winter, when there is very low light. Penetrating light can also be used more effectively when a diffuse screen with high light transmission is used.

Performance versus costs

If the costs of a diffuse climate screen are compared to diffuse coatings and glass over fifteen years, the climate screens come out on top. Can a Harmony screen be used to replace diffuse glass? No, Harmony improves shadow effects so effectively ‘upgrades’ the light generated via diffuse glass. This creates better growing conditions.
Is the greenhouse temperature under a diffuse coating better than under a diffuse screen? No, the results are similar, even on sunny days. Can a Harmony screen be used to replace diffuse coating? Yes, because a coating costs light particularly on cloudy days and in evenings/mornings.

Conclusion: diffuse climate screens are more effective than any other system in spreading light and retaining maximum light benefits and offer comparable performances in relation to lowering greenhouse and plant temperature.  

Kas Magazine

September 2018

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