US2394495A - Diffusing projector lamp - Google Patents

Description

v Feb. 5, 1946. R E, sMlTH 2,394,495

DIFFUSING PROJECTOR LAMP Filed Nov. 21, 1944 [/vvEA/TUR: R/EHARD E EM/TH H/5 ATTUH/VEY Patented F eb. 5, 1946 mrrusmc Pnomo'ron LAMP Richard E. Smith, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Application November 21, 1944, Serial No. 504,434

(on. ne -a4) 3 Claims.

This invention relates to electric lamps, and.

particularly to projection lamps for diffuse illumination. The invention is concerned with controlling the degree or angle of diffusion of the visible or other radiation for such lamps. The invention is very useful in connection with lamps of a general type such as disclosed in U. S. patents to Daniel K. Wright Nos. 2,148,314 and 2,148,315, granted February 21, 1939, and 2,324,972, granted July 20, 1943, commonly known as the Sealed Beam type, and is hereinafter explained in connection with its application to such lamps. Various novel features and advantages will become apparent from the description of species and forms of embodiment of the invention, and from the drawing.

In the drawing, Fig. 1 shows an axial section through a sealed beam type of lamp embodying the invention; and Fig. 2 is a side view of a diffuser slightly different from that shown in Fig. 1, on a larger scale.

Fig. 3 is a diagrammatic illustration corresponding to Fig. 1 and showing a somewhat different type of diffuser.

A sealed beam lamp bulb or envelope I is shown in Fig. 1 as comprising a rear concave pressed glass reflector portion 2 internally surfaced with a reflective metallic coating 3, and a front radiation-transmitting cover portion 4, also slightly concave and preformed out of pressed glass. The reflecting surface 3 of the rear portion 2 is shown as a paraboloid, and the front portion 4 is shown as spherical. The parts 2, 4 may be separately formed out of low-expansion heat-resistant glass such as the borosilicate glass disclosed in U. S. Patent No. 1,304,623 to Sullivan et al., known commercially as Pyrex, and may afterward be sealed together by fusion at suitably mating surfaces.

Within the envelope I, at or in definite optical relation to the focal point 5 of the reflecting surface 3, is mounted the electrical energy-translation means or light source which may consist of a filament 6 of refractory metal extending coaxial with the reflector 3' at and through the focal point 5, which is preferably at mid-length of the filament. Current connections I, 8 may be sealed through the reflector 2 gas and vacuum tight as in Wright Patent No. 2,324,972, and are shown as first extending straight inward and as being then bent toward and parallel with one another, so that they overlap and intersect the reflector axis at opposite sides of the focal point 5. The straight ends or legs of a coiled tungsten fllament 8 are shown as welded to the overlapping lead wire ends I, 8 with the axis of the coil coincident with the reflector axis at the focal point 5. As shown, the wires I, 8 are interconnected, spaced, and braced together inside the reflector 2, behind the laterally bent end of the lead 1, by means comprising an insulating length of hard or quartz glass rod 8 into whose ends are fused short wires III, III whose other ends are welded to the leads I, 8.

For the purposes of the present invention, a diffuser I I is shown around the filament coil 6. in position to intercept practically all or most of the light from the filament that would otherwise reach the reflecting surface 3, but with its interior open into the interior of the envelope I. As shown in Fig. 1, the diffuser I I is of globular or elipsoid form, with opposite open ends I2, I2 coaxial with both the legs of the filament 6 and extending to the overlapping parallel portions of the inleads I, 8, or nearly so. The diffusing globe I I is centered coaxial with the filament coil, preferably with its wall substantially concentric with the focal point 5. The diffuser I I may be mounted and held in this position by means of V-bent wires I3 welded to the parallel leads I, 8 and lying in diametral planes of the ends I2, I2, which concurrently fit on both Vs substantially without looseness or play. The diffuser Il may be of any light-permeable but diffusive material, such as frosted glass, for example.

The effect of the diffuser I I is that its external surface virtually becomes an ellipsoidal light source so far as the reflector 3 is concerned. Accordingly, practically every point on the reflector surface 3 receives a cone of light whose vertical angle is that subtended by the diffuser I I at the point in question, or, in other words, is equal to the angle between tangents It, It -drawn from the point to the opposite sides of the more or less elliptical outline of the diffuser II in Fig.1. From each point I5 where the angle of the tangents I4, I4 is A, a cone of light of the same vertical. angle A 'Is reflected, as indicated by the lines I6, I5. To illustrate this, several such pairs of lines I4, I4 and I6, I6 have been drawn in Fig. 1 for points I5 widely separated on the reflector surface 4. For points II far out on the reflector 3, the angle B between tangents I4, I4 and lines I6, I6 may be less than A, owing to their greater distance from the diffuser II; but it is nowhere greater than A. The direct light from the source 6 issuing through the ends I2 has a much smaller angle of divergence. Accordingly, the projector I throws a cone of light (visible or invisible) whose observed angle of divergence is the angle A. -By making the difluser ll of suitable size, this angle A can be made 20, 30, or practically anything in reason that may be desired. As compared with an incandescent lamp oi the same size as the difiuser II, the candlepower maintenance oi my device is much better, and the light source or filament 8 can be of much higher wattage.

Fig. 2 shows a diffuser ll essentially very similar to that in Fig. 1, but divided into halves which are separated to afford annular opening 18 between them, and without end openings as in Fig.

1. As shown. the filament c0116 extends in the general plane of this opening, perpendicular to the axis of the associated reflector (not shown).

The opening I8 allows circulation of the atmos-. phere in the envelope I around the filament 6.

Fig. 3 illustrates a lamp whose envelope I may comprise reflector and light-transmitting components more or less like those in Fig. 1. Associated with its light source 8 is a difi'user ll' somewhat different from those illustrated in Figs. 1 and 2, in the form of a deep bowl enclosing the source I behind, at the sides, and to a distance forward such that only a cone ofdirect light having the desired angle of divergence or diffusion A gets out. As in Fig. l, the diifuser ll functions as a virtual source of illumination which subtends substantially the desired angle of difiusio'n or di-.

vergence A at all points ll on the reflecting surface 4, while at points I! the angle B is less than A. Thus the device as a whole throws a cone of light of angle A, as already explained in connection with Fig. 1. Y

In Figs. 2. and 3, various parts and features are marked with the same reference characters as those corresponding in Fig. 1, in order to dispense with repetitive description.

.What I claim as new and desire to secure by- Letters' Patent of the United States is:

1. In a diflusing projection lamp for producing a beam of light having a desired angle of divergence, the combination of a sealed envelope comprising a rear concave reflector portion and a front transmitting portion, a light source at the focus of the reflector, and an open difluser in the envelope interposed between the light source and the reflector and correlated in shape with the reflecting surface to subtend substantially the same angle at substantially all points of the re- 3. In a diffusing projector lamp, the combination of a sealed envelope comprising a rear concave reflector portion and a front transmitting portion, an incandescent filament in said envelope extending axially of the reflector at its focus, and an ellipsoidal difi'using globe in the envelope having its major axis substantially coincident with said filament and having end openings opposite the ends'of said filament.

RICHARD E. SMITH.

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