GB1071102A - Electric discharge lamp - Google Patents

Abstract

1,071,102. Discharge lamps. SYLVANIA ELECTRIC PRODUCTS Inc. Aug. 10, 1964 [Aug. 16, 1963], No. 32523/64. Heading H1D. A high pressure white-light-emitting discharge lamp, the filling of which includes mercury and a halogen other than fluorine, has a heater coil surrounding, but disposed behind the emissive end of, at least one of its cathodes, whereby, upon switching on the lamp, the heater evaporates from its surface any condensed material, to provide a clean surface for initiating the discharge. Each main electrode of a lamp having a quartz or alumina envelope 1 (Fig. 1, not shown) is formed of a wire coil (2) wound upon a tungsten or molybdenum core (13), a heater coil 17 (Fig. 2, not shown) being interwound at its end with the coil (2), but thereafter spaced from and encircling the core (13) and connected to a separate lead-in (6). When starting the lamp, the heaters (17) and (15) are in series across the supply, and vaporize metal from their surfaces. With rise in temperature, a circuit-breaker (35) opens to cutout the heaters, whereafter a glow discharge is initiated between the heater surfaces and their adjacent starter electrodes (25) and (23), and subsequently an arc discharge is initiated between the primary electrodes (11 and (13), the starter electrodes being cut-out by bimetal circuit-breakers. It is stated that, in some cases, the starter electrodes may be dispensed with, the initial arc occurring between the two heater coils before transferring to the main electrodes, and that only a single heater coil may be sufficient. Reference is also made to thorium as an additional constituent of the filling.