Is it just the light on the dash that is lit or is the overhead light also on? The dash light won't drain your battery; the overhead light will.
That said, these door switches that control the light are simple contact switches. When the door is open, the button is allowed to spring out inside the switch, completing the circuit. Sometimes the switches get a bit rusty on the backside, allowing the switch to complete the circuit when it shouldn't. Remove each switch by removing the 10MM bolt and pull the switch just slightly out from the door area. No need to disconnect the wiring. It can easily fall inside the door if you do disconnect it. Check the back of each switch for rust. If you do find rust, clean the rust up with a wire brush or some sandpaper and apply some dielectric grease to the area. You can use petrolium jelly in a pinch but dielectric grease is better. Also clean up the bolt and the bolt threads if there is any rust on them. That bolt acts to ground the circuit to the car's frame. Reinstall each switch and check to see if the problem is resolved. This is an easy DIY task.
Mike