Dr. Biswanath Roy’s scientific contributions

Design and development of a daylight responsive automatic dimmer circuit for compact fluorescent lamp (CFL) is presented in this paper. LDR is used as daylight sensor and the variation of daylight level is shown by the output signal generated by LDR circuit. The CFL lamp dimming is done by the variation of the lamp input voltage through variation of firing angles of the triac by using pulse width modulation (PWM) technique. LDR output signal is fed to the lamp dimmer circuit to adjust the CFL lumen output according to available daylight.

In the present work a control circuit for dimming of compact fluorescent lamp has been designed and developed. The dimming is done by varying the lamp’s supply voltage through variation of firing angle of a triac, controlled by the firing pulse generated through Pulse Width Modulation (PWM). The output waveforms generated at the output terminal of every stage of the dimming control circuit are recorded. Experiment has been carried out to know the dimming characteristics of 18 Watt compact fluorescent lamp which showed non-linear relationship of lamp lumen with supply voltage. This characteristic has been incorporated in the developed dimmer circuit.

In recent times it is observed for Kolkata city roads that the conventional High Pressure Sodium Vapour (HPSV) lamps are being replaced by white light sources like Metal Halide (MH-T), Ceramic Discharge Metal Halide (CDMH-T). Moreover in some cases entire HPSV streetlights have been replaced by white LED streetlights. It is being claimed that white LEDs are used for its high efficacy than other lamps. In this present paper a sample city road stretch has been taken as a case to study energy saving potential of white LEDs in comparison with HPSV, MH-T and CDMH-T while meeting all lighting design parameter– National (i.e. IS:1944,1970) and International(CIE 115-1995 and IESNA RP-8-00). The theoretical simulation has been done with lighting design software DIALux 4.9. This study revealed that Unit Power Density (UPD), a parameter connected to installed electrical power, is minimum (i.e. 1.08 Watt/m2) for HPSV lamp and maximum (i.e. 1.79 Watt/m2) for white LEDs –which is more than one and half times the value of the previous one.