This is not to be confused with the amount of illumination reaching the work space. A fixture intended for an incandescent lamp may not distribute light where needed when fitted with a CF lamp. Fixtures are designed for specific lamp sizes and shapes, and light from a different lamp will not necessarily be distributed at optimum efficiency. Lamps and fixtures should be properly matched to avoid occupant dissatisfaction. When existing fixtures must be used, the designer or retrofitter may have to install higher-lumen CF lamps to achieve desired illumination levels.
Flicker can occasionally produce headaches and eyestrain in some people.
The stable nature of phosphorescence smooths out the effect of this cycle, but the instantaneous variations in fluorescent light output known as flicker still occur. The 120-Hz variation is too fast to be seen by most human eyes, but a stroboscopic effect can be observed when rapidly moving or rotating objects are viewed. High-frequency ballasts that send current through the lamp at frequencies up to 40 kHz can be used to prevent flicker problems. In addition, the physical appearance and brightness of luminaires can affect one's impressions of brightness in a space. Light from CF lamps, in comparison to incandescent lamps, is typically more uniformly distributed over a larger portion of the lamp surface area.