The convection phenomena in the high pressure sodium lamp

Abstract

High pressure sodium lamp is known as a light source in which convection phenomena of the arc are so small. Recently, arc tubes with larger diameter and high pressure xenon filling have been used for the HPS lamps with high color rendition or high luminous efficacy. It was found that the convection phenomena were not negligible in such HPS arc tubes. This was confirmed by measuring the 475 nm sodium line intensity and knowing by the displacement of the arc axis. The results are:
(1) The convection becomes larger with increase in arc tube diameter and filling xenon pressure.
(2) The convection becomes smaller with increase in the power input.
The temperature difference between the upper and lowerside of the arc tube wall in the horizontal operation reaches 40-50°C and this local heating of the arc tube will be a problem in the life of HPS lamps.