Can a one-way CFL bulb be used in a three-way socket?
The way that three way sockets work is they have one neutral (the socket threads) and two hots. The two hots are only different in that the four positions of the switch are: Off-Off, Off-On, On-Off, and On-On. If you look at the business end of a 3-way bulb, you’ll see that the two hots are a ring contact and a center contact. A normal 3-way bulb has two elements in it, one that’s a low number of watts and one that’s a high number. A regular bulb (CFL, halogen or regular incandescent) only has the center contact for a hot, so it completely circumvents the ring contact. End result, the four positions of the switch result in the following behavior when you have a regular bulb installed: Off, Off, On, On. The reason the warning is there is because if the contacts are just out of alignment, there could be some sparking from intermittent contact between an oversized center contact and the socket’s ring contact. YMMV, but I’ve used many single-way bulbs (CFL and otherwise) in 3-way sockets a
