Apologies if this is answered before - I haven’t found an answer in the forum.
The Sun Light in Blender takes strength input in the units of W/m2. Earth has a solar irradiance value of 1361 W/m2 - this seems to be really really bright and needs scaling by nearly 10000 times to get something visible. How to model the physically realistic solar irradiance value for the sun emitter? Please help!
I’ve gone through the forum and this source but nothing seems to help!
Hi,
You can try to use the Sky Texture node that could help you to simulate real sun appearance. To find out more about it, I’d suggest to watch this one video below:
As for your main question, I didn’t find anything useful either, except this one below:
Hope it helps
Cheers,
Sergey
Thank you Sergey! But the sky environment texture is for Earth atmosphere (right?). I’m trying to get a realistic light for asteroid like objects. Any suggestions? I am chasing empirically valid models for lighting and textures for a true-to-physics observation.
Try to check out the second video I’ve dropped above
Sure. Can I not get away with using the Sun Light emitter? Why is my mesh so bright with the actual solar irradiance strength?
Maybe it is because of your camera focal length, but I’m not sure. Try to reduce your focal length in your Camera settings.
Well, there you have 4 types of light, which is: Point, Sun, Spot and Area. Two lasts probably won’t satisfy your needs. You can use Point instead, but I’m not sure that it would satisfy you either. Based on that I’d suggest to use Sun Light anyway.
You can bring the scene exposure down, that’s what I do when using the sky texture, since it also defaults to real units.
Thank you @Hadriscus
I explored adjusting the scene exposure (film/color management) for better results. I want to associate photorealism to the rendering result. Can exposure control be associated with realism? I mean the sun light has a strength that the camera model perceive in real-world. I can control the camera exposure but not the scene is too bright in the real-world anyway? I also want to ensure that I’m not using the sun emitter in the wrong way.
Sky texture (Nishita/Pritam) is good and empirical but I’m thinking its only valid for earth (not free space) atmosphere, right?
I would say yes, real world values ensure the shaders react how they’re supposed to, this is also valid for dimensions, the scale of objects. Working to scale makes things predictable.
I’m not sure what the second sentence means, your question ? You would need to lower the exposure, yes. But you don’t have to work like this, you can keep the exposure unchanged and work your lighting from there.
There an altitude component in the sky texture that lets you go hiiiiiigh and mostly annihilate the atmospheric perspective
I would render out a reference image using Nishita sun & sky at default values. Then replace the Nishita sun portion with a sun lamp at correct orientation, re-render and adjust until the sun lamp matches. Use blackbody node to set its temperature for its angle. Iirc - and it’s a big if 
- it should end up around 50-100 strength to match. The source you mentioned is kinda outdated, and even the manual still says “Typical values are around 250 for an overcast day and 1000 or more for direct sunlight.” (closer to your source), and is from before we had Nishita Sun & Sky at strength 1 as a fixed reference light ad we had to “make up” our own system (I wasn’t part of it though).