| abstract |
The efficacy of a high-pressure sodium lamp is increased significantly by enlarging the arc tube diameter and deploying a composite infrared-reflective film on the interior of the outer lamp envelope. The infrared-reflective film acts to maintain the wall temperature of the enlarged arc tube at the same optimum temperature as the arc tube wall in a conventional high-pressure sodium lamp. In one embodiment, the IR reflective film is a multi-layer composite film of In 2 O 3 :Sn or SnO 2 :F overcoated with a TiO 2 or SiO 2 dielectric film. In another embodiment, a three-layer composite film is made up of TiO 2 , In 2 O 3 :Sn, or SnO 2 :F, and SiO 2 films sequentially overlaid on the outer envelope. The dielectric films improve lamp efficacy and enhance the high temperature chemical stability of In 2 O 3 :Sn and SnO 2 :F. Such IR reflective films are substantially transparent to radiation in the visible region of the spectrum, but are highly reflective in the infrared portions of the spectrum. |