In most juridic systems, there is the letter and spirit of the law to deal with that. A judge would settle that detecting that somebody approaches your shop is not in the spirit of the law against surveillance based advertising. And so you'll rapidly have a jurisprudence.

That would seem trivial - the PIR used in such a system isn't recording anything about the person.

A motion-detecting light isn't surveillance. It follows the same principle as your refrigerator light: when someone opens the door, shine the light so that they can see.

Surveillance is the monitoring of peoples activities. A very, very different thing from an energy saving device -- I'd even argue the opposite, as surveillance requires constant energy. To monitor someone in the current system is to literally follow them around. To use your example, surveillance would be placing sensors in your products so that when your customers buy them, you can follow them around and record how they're using it. But I don't think an energy saving light can be called surveillance.

This is what I find difficult about these things, we (mostly) intuitively know that some cases it's okay to use information about users to tweak their experience, while we also know that what Facebook/Google/etc are doing is absolutely wrong. The big question is, where do we draw the (legal) line?