According to the DOE, another issue is that "dimmable" has no standard definition and claims of dimmability cannot guarantee any minimum level of performance. In addition to the differences in the maximum and minimum light output in the dimming range, the rate of dimming may change during dimming. Performance attributes such as LED package efficacy, driver efficiency, complete product efficacy, chromaticity, flicker, and power quality may also change during dimming.
The DOE notes that some phase-cut dimmers change the behavior of some LED lamps, and vice versa.These compatibility problems can result in undesirable behaviors such as changes in dimming rate, dead travel (little or no change in light output despite changes in dimmer setting), pop-on or dropout (sudden change in output not corresponding to the limit of the dimmer signal), flashes or ghosting, audible noise, reduced lifetime or reliability of the dimmer, and reduced lifetime or reliability of the LED product. These challenges result in highly unpredictable LED dimming performance.