Luminous flux to input power ratio, power factor and harmonics when dimming high

This paper presents experimentally obtained luminous flux to input power characteristics of high-pressure sodium and LED luminaires used in road lighting, confirming that when applying dimming scenarios more percentage energy savings can be achieved by an LED than by a corresponding high-pressure sodium lighting installation. However, both workshop and field experiments showed that the tested LED drivers (of either standard or improved dimming characteristics) have the disadvantage of poor power factors (down to 0.67) at low light levels achieved by dimming. In addition, an increased presence of current harmonics and high values of the current total harmonic distortion were noticed at low light levels, representing another serious disadvantage of LED technology regarding power quality. The relevant electrical characteristics of commonly used LED drivers were analysed in detail and the reasons for the poor power quality when dimming LED luminaires were recognised. A new generation of LED drivers with a considerably narrower range of input (AC) voltage will allow acceptable power factors and limited emissions of current harmonics to be achieved in practically all lighting regimes