If you head back to the main Accessibility menu, you can create a shortcut to turn this on and off a little more quickly. Scroll down to Accessibility Shortcut option and tap it. Hit Reduce White Point so a checkmark appears. From now on, you can triple-click the home button to enable the feature, which will dim your phone when it's just too bright. While you're in this menu, you can also check some of the other options. If you do so, then triple-clicking the home button will pull up a menu with all the Accessibility options you've assigned to that shortcut.