[crazygringo]

Do they make "directional" or "angled" Fresnel lenses?

Because you also really want the light to come out of the vertical window at something like a 45° angle downwards.

The physics of it should be fine, I've just never heard of them being manufactured.

And then just add a translucent blue diffusing layer on top.

It seems highly commercializable.

[skykooler]

I suppose you could buy a big Fresnel lens and then cut out a square near the side, and only use that; it would focus the light but also change the angle.

[corty]

There are flat sheets of prisms, that do what you need there. You probably know them from pictures you had as a child that change what they display depending on the angle you are looking under.