Specifically, the lights in question are "outboard" landing lights, and in the photo, one is indeed just burned out. These outboard landing lights are on all of the 737 series from the -100 to the -500, but not on the next generation
(-600 thru -900). On those aircraft, the lights have been relocated to the underside of the fuselage (near the centerline) just forward of the wing. The "inboard" landing lights are the same on all models, located at each wing root behind a plexiglass cover.
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