How can I turn of the green light in back of my watch?

That is the light sensor for taking your pulse. Once you have removed the Watch from your wrist, it should lock and the light go off. The only other option is if you do not have the Watch set to lock when off with Wrist Detection.

connorfromgrinnell wrote:

It’s just the heart rate sensor. No way to turn it off. It’s fine.

...but why is it on continuously? I have never seen or heard of that happening under normal circumstances. I have only briefly seen it on my watch when removing it from my wrist, while it was apparently active.

I would also recommend the Restart which was recommended by ckuan.

connorfromgrinnell wrote:

Pretty sure it’s checking to see if it’s on a wrist. The Watch is designed to be either on your wrist or on a charger. If it’s not on either, it’s probably checking to see if it’s on wrist.

...but (pardon the repeat) why is it on continuously? I just experimented with mine. When I removed it immediately after activating the heart rate function, I briefly observed the light, but it extinguished several seconds after wrist removal. When I removed it without activating the sensor it did not illuminate.

Which Watch Series do you have?

Try Restart Apple Watch - Apple Support

ChrisJ4203 wrote:

The only other option is if you do not have the Watch set to lock when off with Wrist Detection.

That's the ticket!

les06 wrote:

The green light on my apple watch came on and I do not know how to turn it off. Help

It’s just the heart rate sensor. No way to turn it off. It’s fine.

Pretty sure it’s checking to see if it’s on a wrist. The Watch is designed to be either on your wrist or on a charger. If it’s not on either, it’s probably checking to see if it’s on wrist.

👍