Use Vivid to browse the web at your iPhone's full brightness. 

Wether you're reading a long article in the sun or you're browsing through your Twitter feed, with Vivid you'll be able to utilise the full brightness of your screen. Use the Action Extension to quickly open pages in Vivid from Safari or other apps and quickly go back to Safari as well.

Note that Vivid Browser does not work make full screen videos brighter.