Active D-Lighting optimizes high contrast images to restore the shadow and highlight details that are often lost when strong lighting increases the contrast between bright and dark areas of an image. It can be set to operate automatically or manually, and it's also possible to bracket pictures to get one with Active D-Lighting and one without.
The image on the left shows the balanced lighting achieved when Active D-Lighting is turned on. The image on the right was taken with D-Lighting turned off. Notice the dark areas in the foreground of the image.
Active D-Lighting's image optimization, which takes place in the camera at the moment the photo it taken, applies digital processing only to the necessary portion(s) of the image. Even when shooting a subject with a wide dynamic range, Active D-Lighting is able to reproduce a realistic image that retains natural contrast.