Adjust the Nintendo 3DS's Brightness Levels

Unlike many modern backlit devices, the brightness levels for the Nintendo 3DS, 3DS XL, and 2DS don't automatically adjust according to your surrounding light. They need to be adjusted manually. 

Steps to Adjust the Screen Brightness

1. Enter the Home menu by pressing the Home button on the bottom half of the system.
2. Look for a sun-shaped icon on the upper left-hand side of the bottom touch screen. Tap it.
3. Select your desired brightness level. 2 is good if you're in a dark area, whereas 3 or 4 is sufficient for a brighter environment. Remember, the higher the level, the faster your 3DS / 2DS's battery will drain.
4. Tap OK.

Remember, you can enter the Home menu and adjust brightness levels even when you're in mid-game.