Stupid question but what will happen if I switch on a CFL bulb that has a hole in it?


Flashlight Enthusiast
Aug 1, 2007
SW Ohio
The filaments at the tube ends will attempt to light and probably burn out since there is air in the tube and no arc (technically more of a low pressure discharge than an arc) can be struck. The CFL ballast circuit is a simple push-pull oscillator/driver that depends on the electrical load of the arc tube to function. Without that load the circuit is designed to fail due to excessive voltage across the transistor junctions or possibly current shoot through of the two transistors. You'll probably hear a little pop sound as the ballast circuit dies.

I haven't actually investigated how the driver circuit is designed to quietly kill itself at end of life of the CFL tube. Early CFLs often died with smoke and/or odors because the ballast tried to continue to drive a dead tube and it would melt down capacitors inside the ballast. This obviously would scare consumers away from the product so they designed the circuit to die quietly at EOL. I do notice that before the EOL, some CFLs get very hot near the electrodes as the voltage drop there becomes very high and much power gets dissipated. I've seen the glass crack, even melt and the plastic casing near the electrode burn and emit odors. When the glass cracks or melts, air enters the tube and the arc is lost. The ballast circuit will then quietly kill itself.