Adjust Your iPhone 5′s Screen Brightness

Apple gives you the freedom to adjust your iPhone’s screen brightness, so you can set it as high or as low as you want. Although many people set their screen brightness somewhere in the middle, the brighter your screen shines, the faster your battery will drain.

The iPhone’s Auto-Brightness setting also does a decent job of adjusting brightness based on the ambient light around you, but if you’re willing to set the level lower, you can save more juice. Here’s how to adjust your screen brightness manually  to save crucial battery life.
Navigate to the Settings menu, then tap Brightness & Wallpaper.

Toggle Auto-Brightness to Off. This will disable Auto-Brightness, so your iPhone 5 won’t automatically adjust based on your surroundings. Instead, you’ll manually set your screen brightness, which will conserve more battery.
Move the slider as far to the left as you can while still being able to comfortably see your screen. In other words, you shouldn’t be straining your eyes. You want to minimize the brightness, but not by so much that you can’t see what’s on your display.

As you move from environment to environment, you may find it necessary to adjust the brightness manually. For example, if you’re in direct sunlight, you’ll need to pump it up to maximum, but if you’re in a dark place, you may be able to get by with the lowest setting.