There are several factors that can contribute to flickering in fluorescent light bulbs. A fluorescent light bulb's ballast is usually but not always, the cause of flickering in such bulbs.
The Lighting Research Center states that ballasts are employed in light bulbs to control the flow of electricity from a power source to the light source. When a steady flow of electricity to the light bulb is disrupted, the bulb will flicker.
There are two types of ballasts used for lighting including electronic ballasts and magnetic ballasts. Magnetic ballasts are an older technology, fluorescent light bulbs that feature magnetic ballasts are much more likely to flicker than electronic ballasts.
According to Sam's F-Lamp FAQ sources, a defective or cheap ballast may be the cause of a compact fluorescent light bulb's flickering. Ballasts can be replaced but repair costs are steep compared to the costs associated with buying a new bulb altogether.
If a compact fluorescent bulb is loosely fit in its socket, the bulb can flicker. If the mounting plate that the ballast is attached to is loose, the ballast can vibrate causing the bulb to flicker.
Most fluorescent light bulbs are not equipped to be attached to a dimmer system. Compact fluorescent light bulbs may flicker if they are operated on a dimmer switch.