TIMERS -- If the timer is a manual clock type, acting as a simple mechanical “on-off” switch, a CF bulb will work just fine. But if the timer is electronic, there is a 50-50% chance that the electronics of the timer will scramble the electronics of the CF bulb and cause it not to start. The best way to determine compatibility is to call the 1-800 number on the timer’s package and ask the manufacturer.