# What geometry would an artificial sun take in a domed city?

My alien world has advanced to living in domed cities powered mostly by wind. They need to emulate a diurnal sunlight cycle and get the maximum full-visible-spectrum sunlight to the largest portion of the city possible, trying to avoid permanent dark areas, and also trying to make something of a cycle with shadows moving through the day. They certainly don’t need infrared on this world. In other words, it’s not just switch light on at 8, switch light off at 7 or whatever. It can’t be perfect but I think it can draw an arc.

To emulate seasons I was considering rotating the entire geometry through a year, where shadows would merely change orientations in a sinusoïdal cycle.

I was wondering if any pattern can emulate a sun crossing a sky for most of the city. It’s obvious different areas have to get light at different times, I think.

# City Construction

The city dome is constructed by airships with solid insulating material, so it can reach a good height of 120 meters with an 8 km radius (less than 2% grade), buildings are typically 4 stories at best. The city edges are the focus of industry which benefits from access to the outside atmosphere via chimneys. They can be shorter at the edge.

Streets are laid out in a geometry that maximizes light reaching the ground. I was thinking spider web, or offset spider web; ultimately the sun geometry decides this, which tries to get the most light on the ground in the smallest footprint to try to make shadows, so people can have some 3D perspective when walking around.

# Lighting

Light is provided by anti-stokes shift lattice up-conversion of ambient infrared wavelengths. Lattices are arranged to fluoresce many sunlight wavelengths; vapor pressure lamps fill the rest. This arrangement would work best as a permanent mounting switched in segments, but a moving mechanism fits the theme best.

• A few questions: 1. How wide is the biggest city? (assuming more than 240 m so the dome can't be a simple hemisphere, not much of a city otherwise) 2. Is this question just about light (please) or does the artificial sun also need to be the apparent source of heat? 3. Can the "real" sunlight be ignored by assuming the dome is opaque? 4. Are "seasonal" variations required or is repeating the same daylight cycle every day fine? 5. Can it be assume that sustained high-output electric spotlights are available with the available technology? Mar 11, 2022 at 4:11
• @KerrAvon2055 I’ll update in the question Mar 11, 2022 at 4:22