CFLs (compact fluorescent lamps) don’t burn out the way incandescent light bulbs do. Instead, as they near the ends of their lives, they grow dimmer. While some CFL bulbs merely stop emitting light when they finally quit working, others kick the bucket with a dramatic “pop”! sound and then vent a distinct odor. A few even release a bit of smoke at their termination. Sometimes the bases of the bulbs turn black. This seemingly cataclysmic reaction has to do with the breakdown of the bulb’s ballast, which is contained in the part of the bulb that is screwed into the socket. As the bulb ages and degrades, so does its ballast. Yet as scary as odors, smoke, and even blackening of the base of the bulb might be, these lamps are fireproof and are meant to fail safely at the end of their lives.

John Drengenberg, consumer affairs manager at Underwriters Laboratories (UL), said about how CFLs expire: “People expect to see the bright flash and to hear the popping like a traditional incandescent bulb, but the burn out of a CFL is different. The light dims over time and might produce a more dramatic pop, emit a distinct odor, and maybe even release some smoke.”

National Geographic’s Green Guide says of CFLs: “Bulbs burn out when the ballast overheats and an electronic component, the Voltage Dependent Resister (VDR), opens up like a fuse in your home’s fuse box, shutting off the circuit and generating heat and possibly a small amount of smoke. This might sound dangerous, but the VDR is a cut-off switch that prevents any hazards. The melted plastic you’re seeing where the glass coil connects to the ballast is simply a sign that the heat is escaping as intended in the design of the bulb.”

In a nutshell, healthy CFL bulbs may emit a bit of smoke and smell and have burnt-looking bases when they die, but that’s as it should be — there’s no fire danger to any of that, and indeed the bulbs are functioning properly when they act that way.

Read about the Globe CFL legend at snopes.com: CFL Bulb Fire Risk.