Under the FARs, unless the aircraft has a MEL, aren't you required to have everything working? I know a landing light isn't required for VFR flying, but one of my instructors told me that since the aircraft is equipped with it, if it's inop it has to be placarded inop and a maintenance logbook entry made by an A&P. And if you're going to go through that much effort, you might as well just change the damn thing unless you're not planning to use the aircraft at night for a long time.