But people gave you fantastic, in-depth (Romullus) answers.
The default "exposure" in framebuffer is 'arbitrary' (ok it's not I know,..but it's not "sunny f/8", or something common,etc..), so if you place your physical Sun (AND sky in environment, it's one button click within Sun now),
it will be over-bright because:
1) It's fully linear, ie: Highlight compression=1. Solution: Set this to higher number, for example 8.
2) A) Exposure parameter in Framebuffer is set at 0. Set it -2 for example.
OR B) Use photographic exposure (Shutter/Aperture/Luminance) and it will match to your real-life expectations.