US 2181295 A
Description (OCR text may contain errors)
NOV. 28, 1-939. Q, BIGGS 5 AL 2.181295 REFLECTOR BULB LAMP Filed April 18, 1939 Orrick 5132].? a nd SfuafiSDav 1's INVENTORS,
Nov. 28, 1939 UNITED STATES PATENT OFFICE amass moron BULB mm Application Apr-I118, mo, Serial No. scam 1' Claim. (01. ire-icy This invention relates to reflector lamps, and in particular to reflector lamps of the tubular type, with a reflector coating'on the interior of the bulb.
An object of the invention is to provide such a lamp of rugged construction and of long life. A further object is to provide a lamp producing a beam of light freefrom objectionable shadows.
Features of the invention are a mount for the filament of such a lamp, andthe combination of such mount with the proper reflecting surface and atmosphere inside the lamp bulb.
Other objects and advantages of the invention will be apparent from a considerationjof the'following description, taken in connection with the accompanying drawing, in which: I
Figure 1 is a profile view, partly in section, of a lamp according to the invention, and
Figure 2 is an enlarged cross-sectional view of the same lamp.
In Figure 1, the tubular lamp bulb I has the reflecting coating 2 over a portion of its interior surface, and has the reentrant stem l2, projecting into the bulb at one end. The stem l2 terminatesin the press 3 through which the lead-in wires, which also serve as supports for'the ends of the filament M, are sealed. A glass rod or arbor 5, extends out of the stem 12, a molybdenum wire 6 being sealed into the glass button I at the end of the arbor 5, to support the middle of the filament, around which one end of the wire 6 is curled loosely in a small loop 8. One of thele'ad wires 4, is shorter than the other lead wire l5,
and curves outward from. the press toward the reciency when arranged with its axis straight and parallel to the axis of the tubular bulb. The lamp is preferably filled with argon gas at about 600 mm. of mercury pressure, to provide an atmosphere with which the coating 2 will not react and to increase the temperature at which the fllament may be safely operated. The coating 21s preferably an opaque smooth specular reflecting film of vacuum-vaporized aluminum, and may be covered'with aluminum oxide.
The lead-in wire IE will be directly in front of the filament and will cast a narrow shadow.
However, the shadow will be in the straight forward direction, and the light from the reflecting surface will be nearly all reflected in that direction, so that at ashort distance from the lamp the shadow will not be noticeable. To reduce the '8 shadow at short distances from the bulb, the bulb, is preferably frosted slightly, so that the frost will be sufficient to smooth out any irregularities in the beam, but not sufiicient to diffuse the light enough to spoil the narrowness of the 10 beam. The bulb may be frosted over its entire interior surface before the metal coating is applied, and then the reflecting surface itself willbe roughened slightly, which will also tend to diffuse the reflection slightly to avoid shadows. The arbor 5 terminates in the glass button I,
at a'point below the filament, that is at a point nearer to the stem than is the axially perpendicular plane containing the nearest end of the filament, thus not only providing a rugged mount,
but also keeping the arbor and button out of the path of the direct light froin'the filament, thus further tending to reduce shadows. As a further step toward the reduction of shadows, I may, instead of keeping the filament exactly parallel to the bulb axis, turn it to a slight angle, about ten degrees to a plane through said axis, keeping the middle of the filament in a plane through said axis.
As shown in Figure 2, the filament supports 4 a0 and I5 and thefllament H, are all in one plane with the center of the filament supported by, the wire 5 from the arbor button 1. This provides an easily assembled mount, and one which makes the lamp resistant to vibration or jarring. If the supporting wire went back directly to the stem, instead of being supported by the arbor, the whole filament supporting structure might vibrate easily and could be easilyjarred out of place and out of focus. The filament is prefer- 40 v ably placed half-way between the axis of the bulb and the reflecting surface.
The bulb is attached to a lamp base, l6,-which may be of the usual screw type. In order that the reflector lamp may be capable of being turned in its socket through a considerable angle without'breaking the circuit contacting with its terminals, a flexible extension contact H may be soldered or otherwise secured to the usual central contact of such a base, as shown for exam- 5o ple in United States Patent 988,416, issued April 4, 1911,- to M. H. Welsh. A small raised protuberance l3, may be placed on the screw threads at one or more places to insure that the base is held firmly in the socket while being turned.
The part of the lead-in wires inside-the bulb .may be or a soft nickel wire, while the central support wire 6, may be of a stiff molybdenum wire, and the filament of tungsten, to provide a rigid support which withstands vibration and jarring without harming the filament or shifting its position appreciably. r
What we claim is:
In an electric incandescent reflector lamp, a tubular glass bulb, of circular cross-section whose interior surface is lightly frosted to produce a smooth but narrow beam of light from the reflector, one end of said tubular bulb terminating 'in a hemispherical portion and the other end terminating in a reentrant stem, a metallic re,-
flecting coating on part only of the interior frosted surface of said tubular bulb and extending around more than half of the circular crossin a straight line parallel to the axis of the tubular bulb and approximately half-way between said bulb axis and the reflecting surface, leadin wires sealed through the press of the stem,
.end bent back away from the coated portion of the bulb to support the other end of the filament,
a glass arbor extending from the press of the 1 stem along the axis of the bulb and terminating in a glass button nearer to the stem than the axially perpendicular plane containing the nearest end of the filament,'a stiff wire of smaller diameter than the lead-in wires sealed into said button and ex- 1 tending from it substantially parallel to' the bulb axis but bent at the end to support the middle of-the filament coil by being looped around it, and a filling within said bulb of gas inert with respect to said filament and to said metallic reflector coating. ORRICK H.- BIGGS.
STUART S. DAVIS.