For smartphone designers, extending battery life on the devices is a complex dance of sharing a limited amount of milliampere-hours between the cellular radio, the device's display and the processors that are converting digital bits into viewable content. Apple has been awarded a patent for a "Portable media device with power-managed display," which describes a way to adjust the brightness of a smartphone screen depending on what is being displayed.
The patent describes how the content being displayed is identified and categorized as a type (link to PDF of patent document) -- say images, photos, video or an e-book page. If the content shows characteristics of being light in color, the intensity of display brightness could be lowered, saving battery power in the process. For more complex content such as video, the system would sample frames every so often to ensure consistently bright viewing.
Further, the patent delves into user management of the system's auto-dimming. If a user would rather have a steady, bright display at a preset level, they could choose a setting that would make that possible at the expense of battery life. If power efficiency was the user's goal, the system would provide more agressive dimming based on the screen content.
As with all of the patents filed by Apple, whether or not this system actually ever appears in a future product is up to the whims of the engineers.