Excuse me??? I have every right and business to be on my property at any time, day or night, to find out what a stranger is doing on my property!
(Not that you said anything directed at ME personally, but to recommend that he had no justification to go outside ... well, there you go :shocker
That is why I have the 80lb alarm sentry outside ... and when he barks, I get up and go check ... including going outside with whatever level of defense I feel I need at that time ... it is usually the .45, cell phone and my high powered flash light. What I don't do is go out to 'sneak up' on someone ... they are pinned in the spot of the flash light and I or the ex are asking them, "What do you want?"
Personally, I would recommend that the OP turn the porch/outside light on before exiting the house, and to have exited the house from the front door ... yes, he would have been visible in the light, but that is the point. Most BGs are in the dark/out at night for a reason ... to hide in the shadows, so throwing some light on the situation will generally drive the BG to somewhere else.
Just my .02, take it or leave it as you like