With the Sky brightness you can control the exposure of the sky (background) without affect the illumination of the render. For example, Usually when you are rendering an interior using the sun you have to increase the exposure in order to get more light coming to that interior and your sky is completely white (over bright). Now with the sky brightness you can reduce brightness of the sky in order to see the blue sky and still having the correct illumination coming from the sun. The sky Brightness Don’t affect the illumination, only the brightness of the Sky mapping.
Best
sorry to dig up an old topic, but i have found that this isn’t true! if i increase the sky brightness (exterior scene) the illumination of the scene also increases.
the left side is rendered with sky brightness at 1, while the right side is rendered at sky brightness 3. strangely enough, the actual sky image remains unchanged.
the reason i bring this up, is because this thread is exactly about my problem. i want to lighten the image without changing the illumination of the scene.
I’ve always used the physical camera and just adjusted the shutter speed. My rule of thumb is around 50-80 for interior shots and 150-300 for exterior.