Meetprotocol voor lichttransmissie van materialen met condens

Measuring the light transmittance of greenhouse covering materials has become a standard procedure for the
horticultural industry. This measurement is based on dry materials. However, transmittance changes (strongly)
when water condenses on the inside of the material. For example, transmittance of traditional clear non-diffusing
greenhouse glass usually decreases because the condensed droplets tend to reflect the light instead of transmit
it, while some varieties of diffuse glass could increase light transmittance. Because a greenhouse is wet on the
inside during a large period of the year it is important to be able to measure transmission with a standardized
protocol. In this research a measurement protocol and associated equipment are developed for determining the
effect of condensation on the hemispherical light transmission in a standardized way.
The protocol is based on natural condensation on a material under a slope according to common greenhouse roof
slopes, which is forced by a combination of temperature and humidity. In this way the natural process of draining
of condensate is taken into account. The results show that the transmission of traditional clear uncoated (new)
horticultural glass drops with about 3%-points while the effects on the behaviour of the tested types of diffuse
glass vary between -1%- point up to + 1.5%-point.