The atmosphere haze settings.
Main tab
Haze density affects how thick, distance wise, the atmosphere looks.
Haze horizon color is a blend of colors which include the Bluesky horizon color, Bluesky density color and red sky density colors (both are in the tweaks tab)
Bluesky density works on the higher altitudes of the sky. This blends down into the haze horizon density and color. All the above are effected by changing the haze exp height and bluesky exp height in the height control tab.
Height control tab
Haze exp height controls how high the haze occurs in the sky by altitude. Reducing the haze exp height to 500 or 1000 can make for a more smoky or smoggy atmosphere. A use for this is the inversion layer over cities or between mountains/hills. Warmer temperatures above the lower area trap air below this layer; clearer sky above, thicker haze below.
Bluesky exp height can be used to lower the highest sky color so it is closer to the horizon.
I have not used the Ceiling or floor adjustments. I think they would control the depth of the atmosphere. Default settings are Earth like, but other settings used could be for Mars. (Smaller planet and much less altitude for the atmosphere)
Lighting tab
I have not used these too much. The glow amount works on the sun disk and a small area around it.
The glow power controls the scattering of sunlight through the atmosphere. Higher settings make the sunlight create more glow in the atmosphere. A low setting tightens the glow area around the sun, making the glow closer to the sun disk.
Tweaks tab
These can mess up a scene. I use these in very small amounts, because I do not understand how they work very well. The RESET TWEAKS button at the bottom of the tab is great! Remember to use it.
Quality tab
I only adjust the Number of samples. 24 samples with ray traced atmosphere is a high setting. 12 samples will work in many cases.
I have never used Sample jitter. I leave it at the default setting.
Receive shadows from surfaces, controls the sun calculation near or behind the terrain or object/s. It basically will hide the sun's light when it is behind the terrain or an object/s.
There is much more that can be explained. I am only now getting a feel for good lighting in my scenes. My understanding of the atmosphere and lighting settings is still quite basic. Maybe this will help. (There are probably things I have wrong here.)
