Abstract: An alkali metal vapor arc discharge lamp which operates on DC and employs an amalgam of mercury and an alkali metal such as sodium, has a cathode to anode pressure ratio no greater than 5 and a cathode end temperature at least 50.degree. C. hotter than the anode end temperature to prevent cataphoretic separation of the mercury and alkali metal in the arc discharge during operation of the lamp. The lamp is designed to have a cataphoretic driving parameter (CDP) value of less than 150. The CDP is defined as the product of the arc current in amperes, times the arc gap length in centimeters, divided by square of the inner diameter of the arc tube in centimeters.

Abstract: An improved incandescent lamp comprising an inner envelope disposed within an outer envelope is disclosed. The inner envelope contains a halogen gas along with a relatively high pressure efficient fill gas. The inner envelope houses a tungsten filament which is partly surrounded by a separate light-transmissive cylinder. The separate cylinder has on one of its surfaces a selective infrared reflective filter capable of efficiently operating at a temperature range of up to and including about 950.degree. to about 1050.degree. C.