Measuring light in practice
All our coatings are measured annually by the light lab at Wageningen UR. They determine a number of values including direct transmission, hemispheric transmission and diffusion.
Direct transmission is the light that falls at a perpendicular angle to the glass. Hemispheric transmission takes into account the variation in the angle at which the light falls onto the glass during the day. If the light falls onto the coated glass at a smaller angle there will be more reflection, so less transmission.
To better understand how light transmission is affected by a coating under practical conditions, we regularly carry out our own measurements. For this we prefer to take measurements at crop height. The measurements are taken at nurseries where different coatings have been applied next to each other on the same type of greenhouse. Several nurseries have our new product ReduFuse IR next to ReduHeat. Often it appears that the transmission by ReduHeat is higher than that by ReduFuse IR but this is an optical illusion. The diffusion by ReduFuse IR produces a different sort of light pattern; the measurements indicate that there is hardly any difference in PAR light transmission.
We see the same effect when using ReduFlex Blue, which has been used a lot this year on rose nurseries. The greenhouse appears darker inside because part of the blue light doesn’t enter but in practise the transmission is higher than it appears.
During a few large commercial trials, where we compared for example, ReduFlex Blue with ReduHeat, we measured crop temperature and air temperature. In addition, we analysed, together with the grower, crop growth, yield and quality data.
Over the coming years, all this data will form the basis for even more detailed cultivation advice in future.
