US2181291A - Reflector bulb lamp - Google Patents

Description

Patented Nov. 2 8, 1939 UNITED STATES PATENT ,oFFlcE 2,181,291 fnEFLEC'roR BULB LAMP Orrick `H. Biggs, Beverly, Mass., assigner to Hygrade Sylvania Corporation, Salem, Mass., fcorporation of Massachusetts g Application December 7', 1936, Serial No. 114,562

3Claims.

' reflectivity, which retains its brightness throughsure above half an atmosphere.

' ber k691,322 filed September 28, 1933. The iilml out the usual lamp manufacturing procedure and throughout the life of the lamp. This object is attained by the use of Aa vacuum-deposited'aluminum mirror, covered by a thin transparent film of aluminum oxide, in the bulb. of an incandescentlamp filled with an inertgas. At the same time that it protects the aluminum mirror, the oxide lm acts as a getter to remove water vapor from ,the atmosphere of the bulb, thus prolonging the filament life.

Previous attempts to use metal lms for such a purpose have failed because they either required the shielded evaporation of a metal after the bulb was sealed, in which case a .shield remained within the lamp to absorb light, and in vwhich case also it was impossible to secure a sharp cutoff of the reector edge; or if they used a mirror deposited in the bulb before the lamp was assembled and sealed, they used metals which tarnished when subjected to the heat of exhausting-and sealing operations, and which were not protected by a thin transparent film ofl oxide.

vThe present invention overcomes such defects.

The figure .shows a lamp according to the invention. The lamp comprises any usual form of contact base, such as base I in the figure; a glass bulb 2 with a restricted neck 6, and a filament 3. The aluminum mirror 4 may be located in any part of the bulb, but is preferably located on the bowl portion as shown, in orderto be eifective for indirect lighting. The mirror is protected by the thin transparent lm. 5 of aluminum oxide which covers the mirror. evaporation of the oxide film, a lling of an inert gas is provided in thebulb, preferably at a pres- The bulb, if desired, may have ripples orridges on its Vbowl or reflectingportion, for example, as shown in the drawing, to distribute the reecting light desired portion of the inside surface of the lamp I bulb While the latter is evacuated, preferably as described in copending application Serial Numso depositedwill form a metallic mirrorjsurface In order to prevent uncovered by oxide. Air or oxygen is then admitted to the` bulb, causing the formation of a thin transparent lm of oxide over the surface of the metal. If desired,'a heavier protective film of oxide may be formed by means of the Well- 5 known anodic. processes. 'lihe lamp mount may then be sealed into the bulb in the usual manner,

(for the sealing ilame will not affect the aluminum surface, but will merely enhance the oxide coatingv on it. The bulb may then be exhausted, heated 10 .v to drive `oi occluded gases' and iilled with, an

inert gas, vfor example, argon or nitrogen 'in a manner usual in the art. The oxide-coated aluminum mirror will preserve its reectivity throughout this process. y

Such a lamp finds many uses where the light from the lam'p is desired in -certain directions and not desired in others particularly for indirect lighting. In many indirect lighting fixtures, a

vlamp with a metallic mirror coating deposited on the outside of the bulb is now used. The lamp is often placed so that this metal coating is in contact with a grounded fixture. A current can then ow from the hot filament, through the gas inside the bulb,` through the hot glass tothe grounded mirror. The consequent electrolysis and decomposition of the glass leads to early failure of the bulb. The present invention provides an effective, long-lived mirror surface inside thVbulb, thus both insulating the mirror from the grounded fixture and cooling the glass in the region of the mirror, by reflecting the radiation 1 before it hits the glass.

The reflection in the present invention occurs from the surface of the aluminum metal, and not from the surface of the oxide exposed to the atmosphere inside the bulb; that-is, the aluminum metal, and not the oxide, reflects the light. To achieve this result, the oxide must be present in athin translucent layer; and it is preferably present in a transparent layer. l

At the same time that it acts as. a protection for the aluminum mirror, the oxide lm acts as a getter to remove any water vapor which may get into the atmosphere of the interior of .the lamp bulb, the oxide apparently combining iwithvthe water to form the hydroxide. The latter does not spoil the transparency of the oxide film.

This applicationvis a continuation in part of application, Serial Number 623,504, filed July 20, 1932, and of Serial Number 691,322, led Septemf ber 28, 1933. u l

1. In an electric incandescent lamp, a sealed .glass bulb, an opaque light-reflecting layer consisting oi.' substantially pure over part of the inside surface of the bulb, a transparent protective articial coating of aluminum oxide covering the aluminum layer, a wire iilament within the alumium-coated portion of the bulb,

and a lling of argon ata pressure above half an atmosphere within the bulb.

' `artificial coating oi aluminum oxide over .the

aluminum layer, a 'gaseous lling of argon at a pressure above half an atmosphere within the bulb, and a wire lament within the aluminumg coated portion ci the bulb.

pure aluminum extending -over the entire hemispherical bowl portion oi the bulb and a transparent protective articial coating of aluminum oxide covering the said aluminum, the line of cutoff between the coated bowl and the uncoated portion of the bulb being at the place of maximum bulb diameter perpendicular to the longitudinal axis of the bulb, and a lament positioned entirely within the metal coated bowl portion and disposed in a plane perpendicular to the longitudinal axis of the bulb in order to direct the reiiected'light out of the bulb. A

ORRICK H. BIGGS.

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