The motion sensor lights turn on as/when Sam steps out the front door.

[Topstudent]

Inside house:
Sam unlocks the front door and opens it.
Outside house:
The motion sensor lights turn on as/when Sam steps out the front door.

I can't figure out whether is should be 'as' or 'when' here. Can someone please help me? Thank you.

 

[Barque]

If you use "as", it sounds as if you're narrating something that's happening.
With "when", it sounds like a statement of fact, describing what usually happens.

But if you replaced "Sam" with "a person" or "someone", it'd be just a general statement of fact. I'd prefer to use "when" in this case.