Changing a light fixture in the ceiling can be a tricky proposition. You have stand on a ladder juggling tools and wire and somehow hold a ceiling fixture in place over your head while you do it. All of this is difficult enough on flat ground, but what do you do if you have to work over a stairway? Fear not. There's an easy, secure solution for working in stairwells and some suggestions you can use on flat ground, too.
Cut two pieces of 2-by-4 lumber to 48 inches. Hold one of these flush to a stair tread and measure the distance from the other end to the tread or floor below it. Add 1 1/2-inches to this measurement.
Make two rectangles out of 2-by-4. The short side will be 24 inches and the long side will be the measurement you just calculated. Use 3-inch wood screws to join them. Add a diagonal piece that spans from corner to corner.
Lay one more piece of 2-by-4 flat on a stair tread and lay one end of each of the two 48-inch boards on top of it at either end of the short piece. Use the rectangular support piece you just made to hold the other ends of the long boards. Screw all four corners together with 3-inch screws. Verify that the ends of the screws don't protrude or they will scratch the stairs.
Lay a sheet of plywood on top of this frame and screw it down with 1 1/2-inch screws. Test the platform before you use it.
Position your stepladder on the platform and install the light fixture.