I made a video showing an experiment I conducted in an attempt to find out what the “size” value on a sun in Cycles should be to be as close to the real world as possible.
Here is the video: http://youtu.be/qHs2Am55HP4
My conclusion is that 0.005 Blender units (or 5mm if you’re using metric) is pretty close to what the real world looks like.
If you have any comments I’d be happy to hear it! 
Moved from “General Forums > Blender and CG Discussions” to “Artwork > Blender Tests”
thanks very much for the effort! It’s all the details that make the difference. I’ll be using this as my default from now on
Nice video, I (just for “fun”) enabled the YouTube Auto Subtitles, in some parts strange things appeared…
Glad to hear you got use from the video! 
Those can be fun. ^^
Glad you like it!
Unfortunately, with sun size so small shading of some faces is too harsh.
sun 5mm
sun 5cm
sun 5m
p.