LAMPE A DECHARGE A VAPEUR DE SODIUM HAUTE PRESSION

HIGH PRESSURE SODIUM VAPOR DISCHARGE LAMP The specification discloses a high pressure sodium vapor discharge lamp comprising an alumina tube envelope containing sodium, an inert starting gas, a mercury or cadmium buffer gas source and a pair of discharge electrodes. The inner diameter d in mm of the tubular envelope and the average potential gradient E in volt/cm has the following relationship: E ? 37.7-2.05d. The lamp further comprises a radiation suppressing means at least partially surrounding the tube envelope for selectively, and at least partially, absorbing red radiation having wavelengths longer than 620 nm. The lamp achieves a higher color temperature and a higher general color rendering index than conventional lamps of this type without an undesirable increase in the tube voltage, and is suitable for highly efficient indoor illumination.