Wow old thread. Has nothing to do with Airbus, limitations or ILS, because the DC-6 has the same dots. It has nothing to do with 3 position switches since planes like the 737 and the L1011 use two position switches.
The other clue you have is that the Douglas products, up to the 717 use three pieces of white plastic glued to the switch instead of molding it in.
Here's the story. In the bad old days, airplanes didn't have backlit instrument panels. They used red lights that illuminated the panels from the front. When you were on short final and looking for the airport, the lighting of the overhead panel would become an issue. It would cause glare, so you would switch it off. The thing you would need on the overhead panel at this point would be the landing lights.
The three dots were radioluminiscent tritium markers, and later, glow in the dark plastic, to help you find the switches in the dark.