Method of operating HID sodium lamp to minimize lamp voltage variation throughout lamp life

摘要

High-pressure-sodium HID lamps characteristically display an increasing operating voltage throughout life. The industry has established operating standards as a trapezoidal figure on a graph wherein lamp wattage is plotted on the axis of ordinates and lamp voltage is plotted on the axis of abscissas. The parallel trapezoid sides represent minimum permissible and maximum permissible operating lamp wattages and the remaining sides of the trapezoidal figure are two lines of sharply rising positive slope which represent minimum permissible and maximum permissible lamp voltages. The lamp-life operating characteristics are describable by a curve which enters into the trapezoid through the line representing minimum lamp voltages and which exits from the trapezoid through the line representing maximum lamp voltages. To minimize lamp voltage variations throughout normally anticipated life, the lamp is initially operated for a relatively short period of time until the operating voltage is a predetermined value and the wattage consumption is relatively high as compared to the minimum value. Thereafter, the lamp is operated so that the operating characteristic curve of lamp wattage consumption versus increasing lamp operating voltage displays a slope which is negative in nature and which does not exceed an operating wattage drop of about 1.5 percent per one volt increase in lamp operating voltage. Thereafter, the lamp is operated in such manner that the characteristic operating curve ultimately exits from the trapezoidal figure proximate the lower right-hand portion thereof.