Do you have enough light? Measure the ambient illuminance using the light sensor of your Android device. Just tap the LuxNow icon: the current illuminance is instantly displayed floating over your screen, and it automatically disappears in a short while. No need to touch anything to 'close' the app. LuxNow reports the raw illuminance value in lux, and adds short human descriptions like 'Maximum sunlight?', 'Overcast sky?', or 'Indoor shade?'.