I have considered rotating space habitats of various forms for my worldbuilding projects (i.e. cylinders, rings/torii, spheres) and recently discovered this intriguing design by physicist Pekka Janhunen https://arxiv.org/abs/1806.09808
To summarize, the habitat is a squat cylinder that is passively stable in its rotation. It is fairly large (10 km in diameter) to optimize for a number of variables such as structural and shielding requirements, and material expenditure per inhabitant. The cylinder is open on both ends; its inner volume is exposed to space, with two low-g docking ports and tubes that connect them to the cylinder. The equatorial region has substantial volume for "urban block space", which I imagine would be structured as a sort of arcology.
The landscaped part of the habitat housing its biosphere is under a transparent roof 50 meters high, to save on the amount of nitrogen required for the atmosphere. But this layer is itself enclosed within the "light channel", the most novel aspect of the design. The outer layer of the cylinder, half of which will be facing the sun at any moment, is a vast array of parabolic concentrators which funnel light into the channel. The inner surface of the channel is composed of a highly reflective material, such that light fills the volume, even the half that is anti-sunward. Semi-toroidal mirrors at the equator deflect the light by 180 degrees so that it fills the volume directly "above" the rural, landscaped part of the habitat.
Here are a couple cutaway diagrams from the paper to help visualize the habitat as a whole:
The amount of light that reaches the surface is regulated by an array of blinders positioned along the transparent roof, so that diurnal and seasonal cycles can be simulated. The actual design of blinders used is not specified in the paper. This is where my problem arises, and it is a problem I've run into with other habitat designs as well, when mirrors are used to redirect and scatter sunlight.
Essentially, I'm having difficulty visualizing what the sky would look like to a person standing in this rural space, and the ways this could be adjusted using various types of blinding mechanisms and/or different transparent materials for the ceiling 50 meters overhead. The theoretical builders of such a habitat would want to provide a proxy to normal skies for the psychological well-being of inhabitants, and particularly in this case where the roof is only 50 meters high, they would want to prevent a sense of claustrophobia. I know the sky would not have a point source of light as we do with the sun, so I imagine all light would be diffuse, like an overcast day but perhaps much brighter?
I am also unsure as to the scale of blinders that would be preferable to the builders—they could be meters across, or centimeters, or even smaller, perhaps built into the transparent roof itself [in theoretical settings where space habitats are being built I always assume that material science has advanced significantly]. If they were too large I'd suspect that inhabitants could perceive them visually, giving the sensation of being inside a large room, unless the intensity of light was great enough that you couldn't look at the sky directly, which is something I think would be avoided. Small blinders might allow for variations in brightness that feel more natural, like clouds passing overhead, but depending on the size used you're left with anywhere from hundreds of billions to hundreds of trillions of individual blinders which require monitoring and maintenance. In any case, my problem is that I don't have an intuitive sense as to the behavior of light when it is being reflected and scattered in this context.
Hopefully that didn't come across as directionless rambling; I wanted to provide some of my thoughts. To boil it down to the question itself: What would the sky look like in the habitat described above, particularly with regards to illumination, and how do these conditions change when you adjust the size of blinders, or method of blinding? [Note: this is my first question posted on this site. If necessary I will edit it, or add more information]