Today for some reason a small white light at the top of my Moto G 3rd generation started glowing and it won’t stop. Not even when I power off the phone. It didn’t get wet. I didn’t drop it. This just happened out of the blue. How can I turn it off? Will it cause a lot of battery drain while it is on?
I see that no one has responded to your inquiry. Usually, that white LED indicates that the phone doesn’t have enough power to light the screen up…and needs time to power up the battery enough to light the screen. This appears to be a different issue.
I would suggest going into Safe Mode and see if the anomaly continues. If it does not, you most likely have an app that is misbehaving.
I would also suggest performing a Clearing the Cache which remedies many odd behaviors on Android devices, and is something I do as regular maintenance monthly for good measure.
edit: To answer the question “Will it cause a lot of battery drain while it is on?”, no, LED’s use very little power, however, the reason it remains lit may indicate something is going on in the background.