Apparent brightness of LEDs under different dimming methods

High-power LEDs of different color have generated much enthusiasm because of the potential energy savings and reduced maintenance cost due to long lifetimes compared with traditional light source. Two schemes are widely used for LED dimming: continuous current dimming, or pulse-width modulation (PWM) dimming. The visual felling to the LEDs is the most intuitive judgment in the LED illumination and display. But the apparent brightness of the LEDs under these dimming ways has never been studied. In this paper, the research of the apparent brightness is approached through experiments. The results show that when the average intensities are the same, the apparent brightness of the PWM dimming LED is higher than that of the continuous dimming LED. In addition, to the PWM dimming LEDs, the contrast apparent brightness of various color LEDs is obviously discrepant as the duty cycle is less than 40%, but when it is above 40%, the gap between the contrast values becomes much smaller. Thus, in the LED applications, the LEDs using PWM driving method has higher brightness efficacy, and the duty cycle of the PWM should be above 40% to achieve the consistent apparent brightness between LEDs. The results have great availability to optimize the driver for the LEDs.