Questions about rendering with sun

Hi,

I have a question about the rendering with sun. I generate the sun and
sky using
"gensky 3 21 10:00EST -a 40.77 -o 73.967 -g .2". The sun brightness is
6.63e+06. It's a big number. When I render my scene with the sun &
sky, and adjust the exposure. The generated image can be viewed in
http://www.cs.rpi.edu/~shengyu/sunny.png. However, the exposure is
only 4.537687e-02. If the sun light directly reach the
sunlight-redirecting panel in the scene, how can an exposure of
4.537687e-02 can adjust the color in the range of 0 and 1 because the
sun brightness is such a big number?

Thanks.

Yu Sheng