A High Pressure Sodium Lamp with a Improved Color Rendition

High Pressure Sodium Lamps have the highest efficacy of all high pressure discharge lamps and have been commercially available. However, for their poor color rendition, their uses have been restricted to the places where higher color rendition is not required.This paper describes the new high pressure sodium lamp with high luminous efficacy (120 lm/W, at 360 W) and superior color rendering properties (Ra 60) and moreover, being able to be operated on the conventional ballast for the high pressure mercury lamp.For the development of the new lamp, the effect of Xenon was quite important, that is, Ra value increased with Xenon pressure, the same as luminous efficacy.In addition to it, new sealing glass composition and newly designed electrode had been investigated for th e lamp.The former had superior property that high temperature sodium diffusion layer was estimated to be less than 1. 7 mm thickness at 900°C after 10, 000 hours treatment and the latter had good stability of the arc spot at the lamp starting.