This set contains 12 different HDRIs meant to bring beautiful sunsets to your Iray renders.  Each image was made at 8192x4096 resolution for plenty of detail and provides all in one lighting/backgrounds for your scenes.  Included are 6 maps high up inside the clouds as well as 6 maps with clouds high in the sky above.  Those "inside the cloud" presets are perfect for tall mountains or towers and flying aircraft or bird renders, while the others are better suited for cityscapes or landscapes.