Lighting Setup for HDRI Sunset through Clouds

Support Lighting and Rendering
1

Hopefully someone who knows what they are doing can help me with this. The goal is to create a HDRI of a sky with a bright sun, and rainbow colored clouds.

Like this:

sunset

But without the water, I don’t really need a bottom.

I can create clouds that look good (in solid view) with a smoke simulation, but everything falls apart (read: looks like muddy garbage) when I try to create a render with the sun, a background, world volume and the clouds. (It doesn’t help that nice looking clouds take all night to bake and get messed up and need a re-bake if you want to move them).

Before we get to rendering, let me first ask if I have the setup right. I have a panoramic camera at the origin, a single spot light pointed at the camera, the light and camera are inside a sphere with a color ramp of sunset colors on the inside, and the smoke domain is on one side of the sphere.

World%20Setup
World Setup.png879×623 451 KB

Here’s the view through the camera:

Cloud%20Preview
Cloud Preview.png1246×612 410 KB

Clouds look fine here.

So first question, is this even the right approach?

Should this be done with one light like the real world, or is it necessary to cheat on lighting? Ultimately I’d like to use this for lighting an outdoor scene as well as for the sky background.

What material should the dome be? Emission? Something reflective to bounce the one light around?

What intensity should the spotlight be? What beam angle (“size”) should it be? The goal was to have a bright spot that looks like the sun, but with a narrow beam angle the clouds don’t get lit and with a wide beam angle, the circle of the sun disappears.

Here’s some terrible renders with various things turned on and off. They don’t look like what I’m trying to achieve. Part of it might be the freaky panoramic camera angle, and they are low quality to save render time, but you can tell that they don’t look right.

Piece1-sun
Piece3-egg%20sun%2C%20muddy%20colors Piece2-add%20world%20muddy%20colors muddy%20render

The Blender file:
Cloud Sim 7.blend (1000.5 KB)

2

I think what you are looking for is atmospheric scattering.
first you have to know the difference between mie scattering and rayleigh scattering.

in short mie scattering happens if the particles greater than the atmospheric particles,for example water particles,fog clouds mist ect.

rayleight usally is around smaller than 0.25 % of a mie scatter particle to count as rayleight scatter particle.in this case the atmospheric scattering that happens if you see the blue sky.

since the atmospheric particles are scattering the blue “away” the red is left to longer wavelengths(that you dont see,because the particles are to small to be visible or better the blue has much more freqency).

however if the lightwave is hiting the mie particles (clouds)then they are scatter the full colorrange from blue to red(because the water particles are so big,that they scatter all visible colors).this is the reason why you see red clouds if the sun goes down(and white clouds at midday, because the atmospheric way is shorter,and less blue is scattered)

the longer the light path (if sun light goes trough the atmosphere)the more the blue light is scattered and the more reddish all mie particles are in that lightpath way.

here you can play with this atmospheric effect.is quite realistic.then you know how it works.