This is another type of PVC cover where you could get it at the Hardware shop. It is good for 4inch pipe. It was used by my contractor at one of the Stanalone farms.
It holds the PVC pipe tightly as it holds from outside and it is hard to come out. It is tough and best of all it is black in color.
To reduce the light density from the ventilation pipe, use the black cover for external and use the grey color cover for internal. It would reduce the light density in farm.
Young Swiftlets need light to guide them to fly in and out of the farm. The light from Vent-Hole would create confusion if it is not under control. If the Vent-Hole light is too bright young Swiftlets would fly to the Vent-hole and circling around it and couldn’t find the way out.
Secondly to reduce brightness you could also paint the inside of the elbow with black color paint. I would recommend matt finishing type as it doesn’t reflex under bright light.
If you can’t get it at your nearest Hardware Shop you could always call me.
Good Swiftlet farming all!
The Best is to Share and teach!