I think the ethics of the situation turn largely on what's in your mind.

It's been my experience that people who are wondering about the ethics of a course of action often (usually?) do so because they already have a sense that it isn't.

If you're genuinely unhappy with then light, return at at your first convenience. If you're genuinely on the fence about keeping it, then think about it a while then decide to either keep it, with the understanding that you still may return it if it fails, or return it now.

In my mind, you're trying to game the system, and I suspect that you agree, which is why you asked in the first place.