I have a wider beam light on the bars and sometimes a spotlight on my head - when I do have a headlamp, it's a narrow beam one.

It is actually a problem...in the city where I don't need it as much I turn it off. People have said it's great at intersections, but I happen to be fortunate enough to ride most on trails. I think the best thing is to get a narrow beam, then point it just above cars when you look around - won't hit anyone in the face, but you can still see behind you.

I don't think there's a 100% solution - if there was you'd probably get better responses than you're getting here (don't worry you won't blind anyone, you'll blind everyone, it won't function, etc).

P.S. If your headlamp doesn't work in the cold, you got the wrong headlamp. Mine works *better* in the cold (with the battery pack tucked into my jacket), though it still works with the battery pack on the bars, just reduced runtime.