Effects of low duty cycle pulse modulation to the"visual luminance"and efficacy of white LED

Two different kinds of circuit, pulse circuit with 60Hz frequency and 1:7 duty cycle and DC circuit, were used to drive two white light emitting diodes, respectively. Visual luminance of the two LEDs was considered to be equal by 22 observers with adjusting the power of the DC-driven LED, and then the emitting properties of the two LEDs were compared. Our study shows that the measured flux of pulse-driven LED is 66% of that DC-drived LED, this result is consistent with that reported by Masafumi Jinno whose measurement was done at monochrome LED. Meanwhile, the efficacy of the pulse-drived LED is found a little decreased, this could be improved by developing efficient pulse operation circuit.