The Starting Energy of the Discharge Lamps and the Design Criteria of the Ballasts

Abstract

The glow-to-arc transition mechanism of the discharge lamps has been investigated using an idealibed temperature distribution model, wnich is characterized by the following conditions:(1) The temperature of the active part of the electrode is assumed to be uniform.(2) heat current continuity is fulfilled by assuming an appropriate layer (the area is S, the thickness is Δx) between the active part and the rest of the electrode.(3) The transition occurs at the critical temperature Tc.(4) The radiation loss is neglected.The results are(1)The minimum starting energy, which is defined by the electric energy to heat the cathode up to the temperature Tc in the infinitesimal time interval after ignition, is given by mC (Tc-T0).(2) The minimum starting power, which is defined by the electric power to heart the cathode up to the temperature Tc in the infinite time interval after ignition, is given by KS(Tc-T0).Where m and C are the mass and the specific heat of the active part, respectively. T0 is the ambient temperature and K=kΔx, where k is the thermal conductivity of the layer material.The value of mC (Tc-T0) is about 280 joules and that of KS (Tc-T0) is about 42 watts for the 400 watts metal halide lamp.To start the lamp reliably in appropriate time interval more power than the minimum starting power is necessary. The ballast design criteria areVn2/πωL{βcosα+sinα-sin(α+β)-β2/2-Vg/Vn}Vg/Vn>KS(Tc-T0)where Vn is the peak value of the supplied vollage, L is the ballast inductance, Vg is glow discharge voltage, ω is angular velocity of the applied voltage, α and β are the starting and extinguishing phase angles of the glow discharge, respectively.