What's the physical reason that makes compact fluorescent lamps (CFLs) burn out earlier if we frequently switch them on and off?
CFLs typically have a rated service life of 6,000–15,000 hours, whereas standard incandescent lamps have a service life of 750 or 1,000 hours....
The life of a CFL is significantly shorter if it is turned on and off frequently. In the case of a 5-minute on/off cycle the lifespan of some CFLs may be reduced to that of incandescent light bulbs.
In incandescent bulbs, the heating-cooling causes thermal shock in the material making it break eventually. But in fluorescent lamps the gas glows and it can't wear out in the same way the regular filament does. Also the glow only sputters the electrodes when the lamp is on, so this also doesn't explain why switching have negative effects.