Legal demands to keep the surroundings of a greenhouse dark are becoming stronger and stronger. 'Light pollution' harms the flora and fauna near a greenhouse, so is said. That's why screening-producers developed screens with a lightabsorbtion of 85% to 100%.
While at the same time they let pass through as much heat as possible . In The Netherlands a grower is obliged to keep at least 95% of the light inside his greenhouse in the timespan between dusk and dawn.
Of course there are lots of possibilities to achieve the best reduction in light-emission with two screens , one below the other. At the same time ventilation is optimized. And the white colored underside of the screen increases light intensity within the greenhouse. So by using the newest screens the costly energy stays where it belongs, inside the greenhouse. So you optimize the in-greenhouse-climate and reduce the light-emission to the max.
With this technique too, slip-systems must provide the perfect closure and minimal temperature-differences. At the same time at day-time, the smallest possible screen package optimizes light fall and so growth conditions.