For the first time, I put white 50% shade cloth over my 18 ft x 10 ft lean-to greenhouse. Besides reducing light and heat, it diffuses the light.
Notice the white capillary matting on the benches and the reflective plastic sheeting on the right wall. The purpose of the matting is not to water the plants but to raise the humidity and help cool the greenhouse.
Here you can see plastic milk bottles with a pin hole on the bottom to drip water on the matting.
To stop algae from growing on the matting, I periodically spray it with a solution of Physan 20. It is too early to tell whether it works but I can guarantee that, without it, the matting will become an ugly mess. Also, I will have to do something to prevent roots from growing into the matting. It would be nice for the matting to remain a pristine white to reflect light. I know from experience that the matting can be washed in undiluted laundry bleach which removes algae and roots. Unfortunately, the price of laundry bleach tripled during the pandemic.