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What is optimal light distribution?

It is difficult in the greenhouse to measure light well. Certainly on clear days, shadows thrown by parts of the building cause a large difference in the light that falls upon the crop.

On cloudy days when all the light is diffuse, or when using diffuse glass or a diffuse coating, light distribution is much better. The advantage of better light distribution is less variation in growth between the different plant rows. Also the efficiency of photosynthesis improves.

When building a new greenhouse the choice of glass is determined partly by the light transmission values that are specified by the supplier. This is usually the transmission value measured for perpendicular light. If light falls onto the glass at a smaller angle, more light will be reflected so the transmission will be lower. Therefore it is better to compare glass based on hemispheric transmission values. This value gives an average transmission under different angles of light.

How can we determine the light transmission of a greenhouse now?
This can be done with calculation models that take into account the hemispherical transmission, structural parts and light scattering. However, it remains difficult to take into account all the structural parts and the influence they have on each other. Measuring the light transmission is possible but a large number of light sensors are required. We assume a minimal of 20 measuring points in the greenhouse spread over an area of 30-40 m². At the same time another measurement is taken outside. The light transmission of the greenhouse can be determined by using the average of all the measurements in the greenhouse and the one from outside.

ReduSystems has carried out a series of measurements according to the method above to see the effect that ReduFuse has on light distribution in the greenhouse. These measurements show that the light distribution is clearly improved when using ReduFuse and light transmission hardly decreases. The graphic below clearly shows that the difference between maximum and minimal radiation when using ReduFuse is much smaller than in a greenhouse with clear glass. The data below was collected on a clear day. When the sky is completely clouded over and therefore the light is mostly diffuse the difference in light distribution between glass covered in ReduFuse and clear glass will be much smaller.

Left: Light distribution at sunrise under ReduFuse. Right: Light distribution at sunrise under untreated clear glass.

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