From Home Depot.
"Dimmable CFLs are designed to work with fixtures wired to a dimmer switch. A dimmable CFL cannot produce the same range of light levels as an incandescent bulb connected to a dimmer, however. Dimmable CFLs typically dim down to about 20% of total light output. Below that, the bulb switches off. If you want to use a CFL with a dimmer switch, make sure you choose a bulb with “dimmable” on the packaging."
Compact Fluorescent Light Bulbs Buying Guide