The effect of capacitance on drive current of general lighting LED luminaires

The reliability of a LED luminaire depends on the reliability of each of its subsystems. Experience suggests that, of these subsystems, it is the LED driver that tends to fail earliest. Any LED driver has an electrolytic capacitor to limit the ripple current, which helps the luminaire to function appropriately. This paper describes the effects on ripple current of changes in the capacitance and thus on LED luminaire performance. A capacitor bank is developed containing electrolytic capacitor combinations to obtain 27 capacitance values in the range 0.017 to 1570 µF. Two commercially available LED downlighter luminaires of the same model and manufacturer were used for this study. The ripple current and lumen output values are observed after connecting each capacitance from the bank, and the percentage flicker is calculated. LED light output shows visible flicker for low capacitances up to 0.1 µF with percentage flicker above 100%, while percentage flicker for capacitors up to 100 µF is more than 50%. For capacitance values of 220 µF and more, the percentage flicker is less than 50%. For the LED driver the capacitor decides the amount of ripple in the output current, so this work helps in formulating metrics for determining the service life of LED luminaires.