Mike:

I think what you're asking is whether the roads between Northport and points west are safe to ride at night. I would say that the route I suggested via Pulaski Road would be a death trap after dark. In fact, there's one pretty substantial section that passes by an old farm on a two lane straightaway with no lights at all. Kids like to "open it up" on this road because there are no cops around.

Regarding your personal safety in neighborhoods you'll pass through, Huntington Station is not the safest area at any time of day. It's a small stretch, but you'll undoubtedly get stuck at the light on NY Avenue and, depending on how dorky your biking gear is (insert smirk here), you might be made to feel a little uncomfortable. Or you might not.

The more I'm thinking about this whole thing, the more I think you might want to set up your commute so you can take the train all the way home when it's dark at night. That last ten miles or so between Hicksville/Syosset/Cold Spring Harbor and Northport are probably the darkest, most dangerous miles of your proposed commute.