Wouldn't it be easier to just put in a dimmer switch? Or perhaps to switch to appliance bulbs.I think some of those disks caught fire.
A 3A, 400 PIV diode may work for up a 60w incand. My two front 40w lights keep burning out so I may put a diode in each, but in free air inside the lantern box, not in the socket.
Or, wire the two lamps in series at the junction box, if the brightness isn't too uneven.