The Study Of Phantom Array Effect In AC LEDs

Compared with DC LED light source,AC LED can be directly drived by AC power without AC/DC converter and constant current source,and it's cheap with long service life.However,its temporally intensity fluctuation can result in visible temporal artifacts in the light output,such as flicker,the stroboscopic effect and the phantom array effect.These temporal artifacts not only impair lighting quality,but also affect users' comfort and even safety.This thesis is dedicated in studying the phantom array effect of AC LEDs.The visibility of phantom array effect were investigated using the psychological evaluation methods in different cases.The AC LEDs were driven by a programmable waveform generator.Firstly,pilot experiments were conducted to determine the formal experimental set-up.The results show that whether the fixation points are still or moving,as well as the saccade amplitude,have no significant effect on the visibility of phantom array effect.Up-down-ratio of step size has significant effect on the visibility of phantom array effect.Larger up-down-ratio of 3 can effectively increase the accuracy of experimental results.Thus,in formal experiment,still fixation point and 400° saccade amplitude were adopted,and the up-down-ratio were set to be 3.Secondly,the influence of frequency of driving sine waves on the visibility of phantom array effect was studied.With the increasing of frequency,visible threshold of phantom array effect shows a trend of U shape.Between the range of 600-900Hz,the phantom array effect is most visible.Based on this results,the reason of U shape was analyzed in principle.Finally,the effects of driving waveforms on the visibility of phantom array effect were studied.The results show that there is a certain proportional relationship between the visibility threshold of phantom array effect when LEDs are driven by square wave and sine wave.The proportion is almost the same as the flicker index ratio of sine wave and square wave.