[Paul B]

I have a few problems with the design but it would still work with a lot of maintenance.
In the first picture with the enclosed box, algae would grow on the inside of the box weather it was underwater or not. It will always be damp enough for algae. The water splashing on the sides will cause the light to diminish greatly very quickly. You can't use the plastic wrap method wery well because it would melt.
You can modify the box to be a little wider and put the screen in on an angle from top to bottom, put the light over the top and solve those problems but the unit would have to be larger and you would only be able to light one side of the screen.
I am not crazy about any method where there is plastic between the lights and the screen.
Whatever method you finally come up with I use plastic window screen but I first sandpaper it very well then rub wet cement over the screen. That will cause a thin layer of cement to stick into the sand paper scratches greatly increasing the growth of the algae.
Algae love cement. Thats the method I use in my trough which by the way uses no seperate pump or light.
Keep designing, You will get all the bugs out after many models and modifications.