Answer to: Ambient Light Sensor Not Working?Instructions Grab a flashlight or go to a dark room. This might sound like a joke, but bear with us, since the end results are completely worth it. Launch the stock Settings app on your iDevice and head to the ‘Brightness & Wallpaper’ section. Turn off the ‘Auto-Brightness’ toggle. If you went into a dark room and there is no light around, drag the brightness slider to its minimum level. For those who can’t find a dark place, hold a flashlight (or any light source) as close the iPhone’s screen as possible, and crank the slider to the maximum. Now that you have calibrated the sensor, toggle on ‘Auto-Brightness’.