I love pointing out the history of the Refreshment Corner at Disneyland. For example, I point out the Coca-Cola Tiffany lamps and mention that Coke is one of the few-remaining Opening Day sponsors still in Disneyland today? While that's an interesting bit of trivia, it's not nearly as fun to see as the famous red and white light bulb.
The legend of the bulb is that when Disneyland was being built in the 1950s, Walt Disney wanted all the red and white bulbs at the entrance of Refreshment Corner to alternate. But, upon realizing there were an odd number of bulbs, suggested one be painted half white and half red to keep the sequence going.
How to find it? Walk to the exterior corner door and look up and to the right.