Rendering Using Sky Images as Light Sources

I rendered the following bunny images in Photorealizer using equirectangular HDR sky images as light sources.

Bunny at sunrise / sunset.

Bunny during twilight.

Below are LDR versions of the sky images that I used for the bunny renders above. These are the same images that I posted and described in the previous post.

Sunrise / sunset.

Twilight.

Note the realistic deep blue tone of the twilight images. This blue is a result of ozone absorption. Without ozone, these images would be a dull gray.