US3325679A

US3325679A - Electric projection lamp having specially configurated envelope

Info

Publication number: US3325679A
Application number: US435589A
Authority: US
Inventors: Emmett H Wiley
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-02-26
Filing date: 1965-02-26
Publication date: 1967-06-13
Anticipated expiration: 1984-06-13
Also published as: GB1113407A; NL6602311A; DE1299905B

Description

June 13, 1967 E. H. WILEY 3,325,679

ELECTRIC PROJECTION LAMP HAVING SIECIALLY CONFIGURATED ENVELOPE, Filed Feb. 26, 1965 5 Sheets-Sheet 1 Figl.

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June 1967 E. H. WILEY 3,325,679

ELECTRIC PROJECTION LAMP HAVING SPECIALLY CONFIGURATED ENVELOPE Filed Feb. 26, 1965 5 Sheets-Sheet 2 H \iq His A td: FTWH lnven tov: Emme t lr l-LWiLe June 13, 1967 E. H. WILEY 3,325,679

ELECTRIC PROJECTION LAMP HAVING SPECIALLY CONFIGURATED ENVELOPE Filed Feb. 26, 1965 3 Sheets-Sheet 3 ITWVEBTTLOTI Emmett HWILe b9 Q27 [5 His AfttO neg United States Patent M 3,325,679 ELECTRIC PROJECTION LAMP HAVING SPECIAL- LY CONFIGURATED ENVELOPE Emmett H. Wiley, Chesterland, Ohio, assignor to General Electric Company, a corporation of New York Filed Feb. 26, 1965, Ser. No. 435,589 6 Claims. (Cl. 315-71) This invention relates generally to electric incandescent lamps comprising a sealed glass bulb containing an incandescible filament, and more particularly to projection lamps of the type comprising an internal reflector.

In lamps designed for use in film projectors, such as movie projection for home use, restrictions on physical size are imposed by the compactness of the housing in which the lamp is to be placed. In lamps having an internal condenser reflector, this siZe limitation has a direct bearing on the performance of the condenser optics. To be fully effective as a condenser, a reflector must be as large in diameter as the diameter of the cone generated by the limiting rays through the film gate and lens aperture.

It is therefore an object of the present invention to provide a lamp having a high degree of compactness and optical eflectiveness. It is a further object to provide a novel bulb construction which permits moving the reflector closer to the face of the bulb and therefore closer to the projection aperture or film gate, whereby the same sized reflector will more completely fill the lens aperture system and provide more light and better uniformity of illumination. It is a still further object to provide this improved performance without changing the standard base and socket location and preferably with no change in bulb dimension along the optical axis.

Briefly stated, and in accordance with one aspect of the invention, the above objects are achieved by providing a bulb having a main tubular portion which is non-circular in cross-section and has a flattened front face with the concave reflector facing said flattened face and having its mouth in a plane adjacent to said face. In a preferred form, the cross-section of said main bulb portion may be described as being of generally partial elliptical form with a rear face of partial circular form and sides flaring divergently toward the widened and flattened front face. In a further preferred form, the said main bulb portion terminates in a generally cylindrical neck portion having its axis coincident with the axis of the circular rear face portion of the bulb and sealed to a circular stem member which carries lead-in and support wire members from which the reflector and filament are supported, with the reflector offset from said axis toward the flattened front face of the bulb.

Further features and advantages of the invention will appear from the following detailed description of species thereof and from the drawings wherein:

FIGS. 1 and 2 are fragmentary diagrammatic representations of optical systems of a movie projector;

FIG. 3 is a fragmentary diagrammatic representation of an optical system incorporating a lamp in accordance with the invention;

FIGS. 4 and 5 are top and side elevation views of a lamp bulb prior to assembly with the rest of the lamp components and having a shape in accordance with the invention;

FIGS. 6, 7 and 8 are a top view and two side views of another bulb shape in accordance with the invention;

FIGS. 9, 10 and 11 are respectively, side and front elevations and a top view of a completed lamp comprising the invention;

FIGS. 12 and 13 are rear and side elevations of a modified lamp having a ballast filament behind the reflec- Patented June 13, 1967 tor in accordance with a further feature of the invention; and

FIG. 14 is a section of the bulb of FIGS. 12 and 13 along the line 1414 in FIG. 12.

In order to be fully effective as a condenser, a reflector (preferably of ellipsoidal shape) must be as large in diameter as the diameter of the cone generated by the limiting rays through the film gate and projection lens aperture. As illustrated in FIG. 1, for a distance L behind the film gate G, the reflector must be a minimum diameter D to be fully effective. The greater the distance L from the film gate G, the larger D must be.

In actual projection equipment there is usually some space required behind the aperture or film gate for shutter mechanisms such that a lamp bulb must be some minimum distance away from the aperture, usually on the order of one-half to one and a half inches in an eight millimeter projector. For the angle shown in FIG. 2 and the indicated allowance for shutter room S, a tubular cylindrical bulb would need to be of the size indicated as T20, 2 /2 inches in diameter, in order to enclose a reflector large enough to fill the pick-up cone. Even this size bulb Would not allow the reflector clearance needed for normal manufacturing tolerances. Furthermore, this larger size and volume of merely larger bulbs are undesirable. For the smaller bulb sizes indicated in FIG. 2 by the letter T (for tubular) followed by a numeral, the numeral designates bulb diameter in eighths of an inch.

Referring to FIG. 3, in order to overcome these problems, the cross-sectional shape of the bulb B may be as represented n said FIG. 3. The bulb may be said to be bulged laterally to permit moving the reflector R close to the flattened front face f.

Referring to FIGS. 4 and 5, there is shown one form of bulb 1 prior to its assembly with the rest of the elements of the lamp, part of which are indicated in broken lines in FIG. 5. As shown in FIG. 5, the bulb 1 is of standard cylindrical (circular cross-section) form in the sealing area indicated generally by the numeral 2 at the lower part of the bulb which has a longitudinal axis A. However, the main tubular or reflector area of the bulb indicated at 3' is bulged or expanded to allow adequate clearance for any reflector narrow enough to pass through the cylindrical portion 2. The main portion 3' of the bulb may be said to be of generally semi-elliptical shape in cross-section having a partial circular rear face r (FIG. 4) joined by divergently flaring sides s to the flattened front face at the opposite side of the axis A from the rear face r.

Referring to FIGS. 9 to 11, the bulb 1 is joined to a so-called mount structure comprising a glass stem 3 which may be of the flat disc-shaped or button stem type having lead-in and support conductors or

pins

4, 5, 6 and 7 (FIG. 5) sealed therethrough and which support the reflector 8 and filament 9. The reflector 8 may be of a wellknown sheet metal type or, as herein illustrated, of the glass base type such as shown in Patent 3,160,776 to Cardwell et al., and having on its inner concave surface 10 (FIG. 10) a reflecting coating of metal such as vapordeposited aluminum or silver, or a multiple layer interference film or dichroic coating which reflects light and transmits heat. The reflector 8 is supported on laterally extending inner lead wire portions 11 and 12 which also support the filament 9 in accurate predetermined relationship to the reflector 8. Each of the inner lead wires extends through an opening in the reflector and is insulated therefrom in known manner by

ceramic members

13 and 14 in said opening. The said lead wire portions 11 and 12 are, in turn, supported from and electrically connected to vertical inner

lead wire portions

15 and 16 which may be welded at respective ends to said lateral 6 and 7 by bowed or

arcuate wire braces

17 and 18 which are welded at respective ends to the respective vertical

lead wire portions

15 and 16 and to said pins 6 and 7.

Each of said

braces

17 and 18 is also preferably welded V to a wire stud 19 (FIG. 9) having an end embedded in a boss 29 on the back surface of the glass base reflector 8. The stem 3 is also provided with a glass exhaust tube 21 (FIGS. and 9) for exhausting and gas filling the bulb 1.

In accordance with conventional practice, the mount assembly comprising stem 3, reflector 8 and filament 9 and associated support structure, is first assembled with the filament 9 located in exact predetermined relationship to the reflector 8. It is then assembled in sealing relation with the bulb 1 as indicated by the fragmentary showing of the mount in FIG. 5, and the seal area 2 of the bulb is heated by gas burners to soften it and cause it to collapse down into a generally cylindrical neck portion 22 (FIG. 9) which has its axis coincident with the bulb axis A and which is fusion sealed to the periphery of the circular stem 3, the remainder of the bulb 1 below said stem 3 being severed by sharp gas flames. The bulb is then exhausted through the tube 21 and filled with gas, such as nitrogen, after which the exhaust tube is tipped off as shown in FIG. 9. A conventional base 23 may be secured by cement 24 to the bulb neck 22.

The reflector 8 has its sides cut away along parallel cords as best shown at 25 in FIG. 10, in order to permit the use of a reflector of as large a diameter as possible to be passed through the cylindrical portion 2 of the bulb.

It will be noted from FIGS. 9 and 11 that the bulged bulb shape permits moving the reflector 8 closer to the face 1 of the bulb and therefore closer to the aperture or film gate of the projection apparatus than in conventional cylindrical bulbs where the mouth of the reflector 8 is substantially in a plane including the bulb axis A in order to permit use of a reflector of maximum size. For example, in a standard prior art lamp having a tubular bulb of about 1 /2 inches diameter, the face of the bulb is 1 inches from the aperture and the reflector of 1% inches diameter has its side cut away to leave a width of 1% inches. This width leaves enough clearance in the bulb for manufacturing variability without the reflector touching the bulb if the reflector is placed near the center of the bulb. The reflector in this standard position does not completely fill the pick-up angle of an eight millimeter aperture and a one inch f/ 1.6 projection lens with which it is normally used.

on the other hand, in a lamp having a bulb shape as shown in FIGS. 4, 5 and 9-11 and designated TB12, i.e., a tubular bulged shape with a cylindrical portion 2 of about 1 /2 inch diameter, the width of the reflector '8 can be almost as large as the inside diameter of a T12 bulb (tubular, 1 /2 inch diameter) since the bulges allow generous clearance once the mount structure is in position in the bulb. The new bulb shape in this case permits locating the reflector about inch farther forward so that the same sized reflector will more completely fill the lens aperture system and provide more light and better uniformity of illumination.

, This improved performance is accomplished with no change from standard base and socket location since the axes of the base 23 and bulb neck 22 are coincident with permit larger reflectors to be used, the reflector size is still limited to that which will pass through the cylindrical 4 portion 2 of the bulb. However, even larger reflectors may be used with a bulb 1a blown to the shape shown in FIGS. 6 to 8 wherein the entire effective length (i.e, exclusive of the cullet 26) is of the same shape in crosssection as the bulb of FIGS. 4 and 5.

While the glass stem portion of the mount structure might be of a shape corresponding to that of the crosssection of the bulb 1a, it is preferable to use the same circular stem 3 of FIG. 9 so that the finished lamp is the same as in FIGS. 9 to 11. For this purpose it is preferable to form the bulb 1a with appropriate glass distribution or thickness which becomes uniform and round when driven down or contracted by the sealing fires to formthe neck portion 22 (FIG. 9). A glass distribution in which the wall thickness is approximately inversely proportional to its distance from the center line, or axis A, may be used.

More particularly, if the bulged or generally partial elliptical form is blown from a bulb of originally uniform circular cross-section tube, the glass walls in the bulged portions will be thinner than in the unbulged rear face portion 1'. When the bulbs are placed on a sealing machine, with the

mount structure

3, 8, 9, etc,, of FIGS. 9 to 11 located therein as represented in FIG. 5, the bulged or expanded portions heat up fastest because they are thinner and shrink back in a manner that returns the glass to its original uniformity by the time it approaches the button stem 3 (FIGS. 5 and 9) to which it is sealed. It will be understood that, in accordance with standard sealing practice, the assembly of bulb and mount. is rotated about its axis A relative to the sealing fires.

With bulbs of the shape shown in FIGS. 6 to 8, lamps have been made in which the reflector width is greater than the front to back (r to j) dimension of the bulb.

Lamps of the type shown in FIGS. 9 to 11, and employing a single coiled-coil filament in 150 watt rating, have satisfactory strength for projection service in 21 volt designs; but not in volt designs. For operation directly from a 120 volt home current supply, the lamps are provided with a ballast filament connected in series with the effective or main lighting filament. Such ballast filament has heretofore been located at the front of the reflector in a vertical position below the effective main filament.

In accordance with a further feature of the present invention, the ballast filament of the high voltage type lamp is advantageously located behind the reflector, this feature being made feasible because of the substantially greater space between the back of the reflector and the rear face of the bulb in lamps made in accordance with the present invention.

Such a lamp is illustrated in FIGS. 12 and 13 wherein corresponding parts are designated by the same numerals as in FIGS. 9 to 11 with the addition of the letter b. Thus, the bulb 1b is of a similar shape as the bulb 1 of FIGS. 9 to 11, but in this case it is of smaller size designated TB12, i.e., a nominal diameter of 1 /2 inches, as compared to a TB14 or nominal diameter of 1% inches in FIGS. 9 to 11. In this case, the reflector 8b may be of the sheet metal type which may consist, for

example, of copper sheet which may be plated with nickel and then coated with vapor-deposited silver. The said reflector 8b may be supported from the inner ends of the

front pins

6b and 7b (7b being behind 6b in FIG. 13) through a curved brace wire 27 which is welded to said

pins

6b and 7b and is secured to tabs 28 on the reflector. Alternatively the reflector may be formed with tabs which are so spaced that they can weld directly to

front pins

6b and 7b. Of course, other variations are possible. The inner lead wire portions 11b and12b are i in this case shown by way of example as arranged one above the other, with the coiled-coil filament 9b vertically disposed therebetween, and they extend in known manner through openings in a ceramic insulator 13b in an opening at the apex of the reflector 8b. A rigid vertical lead wire portion 16b is welded to and between the inner end of the pin 5b and to the end of the lead wire portion 11b at the rear of the insulator 13b.

In accordance with the invention, a ballast filament 29 of coiled-coil tungsten wire is located behind the reflector 8b and is electrically connected in series with the effective lighting filament 9b by connection thereof between the lead wire 12b and the inner end of the pin 4b. A fuse wire 30 may also be interposed between one end of the ballast filament 29 and the pin 4b and it may, if desired, be enclosed in an insulating tube 31 (FIG. 12) such as glass. In some cases, the fuse 30 may be omitted and the ballast filament 29 itself may function so as to quench the arc formed upon burn-out of the filament 9b and thereby obviate the need for the fuse. In that case, the ballast filament 29 may be connected directly between lead wire portion 12b and pin 4b.

The location of the ballast filament 29 behind the reflector 8b is made practicable by virtue of the bulb shape and the location of the reflector in an offset position towards the front face fb, thereby leaving adequate room between the back of the reflector and the rear face rb for the filament and, if desired, a fuse.

The relocation of the ballast coil 29 to the rear of the reflector provides several advantages over the prior art structure wherein the ballast filament extended vertically below the filament 9bfrom the lead wire 12b and was connected to a wire which extended laterally under the reflector 8b through a fuse wire section to the pin 4b. One advantage of the physical separation of the effective filament 9b and the ballast filament 29 is that at burn-out of the filament 9b ions are formed which start an arc. With the prior art design, this arcing process continued from the top of the main filament coil 9b down through the ballast coil to the fuse. This long sustained arc is detrimental and may generate excessive heat and/or splatter metal on the relatively fragile bulb. In the present arrangement, as the main filament coil 9b fails and ionization begins, the ballast coil 29' drops more voltage and suppresses the arc in the main coil, assisting the fuse in stopping the are or, in some cases, eliminating the need for a fuse.

The location of the ballast coil 29 behind the reflector isolates it from the window area or front face fb of the bulb. This window area becomes very hot and is susceptible to violent failure if contacted by molten metal or arcs. With the present construction, any arcing may be quenched and fusing action may be confined behind the reflector away from the critical front window area. It also avoids the reflector forming unwanted images of the ballast filament which images can be annoying heat or light problems.

The new design also contains fewer parts and is more simple. The spaces involved are also much greater. Even in the absence of the fuse 30, if the ballast coil 29 arcs and burns out it will open into a gap many times longer than the prior art fuse. There is less loose metal at burnout. In the prior art design the sustained are converted both main and ballast coils and the loose end of the fuse lead wire into hot projectiles; this does not occur in the construction disclosed herein.

It will be understood by those skilled in the art that while structural details of presently preferred species have been shown and described herein, they may be widely modified within the true spirit and scope of the invention as defined in the appended claims.

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

1. An electric projection lamp comprising a glass bulb having a main tubular portion having a flattened front face portion and closed by a glass stem member sealed to the end thereof, a separate concave reflector within the main portion of said bulb and facing said flattened front face portion with its mouth adjacent to said face portion, a filament in predetermined relation to said reflector and between said reflector and said flattened face portion of the bulb, current supply and support members supporting said reflector and said filament and having portions thereof sealed in and supported from said stern member.

2. An electric projection lamp comprising a glass bulb having a main tubular portion terminating in a cylindrical neck portion closed by and sealed at its end to a circular stem member, said main tubular portion having a flattened front face portion, a separate concave reflector within the main portion of said bulb and facing said flattened front face portion with its mouth adjacent to said face portion, a filament in predetermined relation to said reflector and between said reflector and said flattened face portion of the bulb, current supply and support members supporting said reflector and said filament and having portions thereof sealed in and supported from said stem member.

3. An electric projection lamp comprising a glass bulb having a main tubular portion of generally semi-elliptical cross-section with a flattened front face and terminating in a generally cylindrical neck portion, a circular glass stern member sealed to and closing said neck portion, a separate concave reflector within the main portion of said bulb and facing said flattened front face with its mouth adjacent thereto and of a size closely approximating that of said front face, a filament in predetermined relation to said reflector and between said reflector and said front face, and current supply and support members supporting said reflector and said filament and having portions sealed in and supported from said stem member.

4. An electric projection lamp comprising a glass bulb having a main tubular portion including a partial cylindrical rear face joined by divergently flaring sides to a flattened front face, said front and rear faces being at opposite sides of the longitudinal axis of said cylindrical rear face, said main tubular portion terminating in a reduced cylindrical neck portion having its axis coincident with said longitudinal axis, a circular glass stem member sealed to and closing said neck portion, a separate concave reflector within the main portion of said bulb and facing said flattened front face with its mouth adjacent thereto and offset substantially from said longitudinal axis toward said front face, a filament in predetermined relation to said reflector and between said reflector and said front face, and current supply and support members supporting said reflector and said filament and having portions thereof sealed in and supported from said stern member.

5. An electric projection lamp comprising a glass bulb having a main tubular portion including a partial cylindrical rear face joined by divergently flaring sides to a flattened front face, said front and rear faces being at opposite sides of the longitudinal axis of said cylindrical rear face, said main tubular portion terminating in a reduced cylindrical neck portion having its axis coincident with said longitudinal axis, a circular glass stern member sealed to and closing said neck portion, a separate concave reflector within the main portion of said bulb and facing said flattened front face with its mouth adjacent thereto and offset substantially from said longitudinal axis toward said front face, a filament in predetermined relation to said reflector and between said reflector and said front face, current supply and support members supporting said reflector and said filament and having portions thereof sealed in and supported from said stem member, and a ballast filament located behind said reflector and electrically connected in series with the firstmentioned filament.

6. An electric projection lamp comprising a glass bulb having a main tubular portion of generally semi-elliptical cross-section with a flattened front face and terminating in a generally cylindrical neck portion, a circular glass stem member sealed to and closing said neck portion, a separate concave reflector within the main portion of 7' V 8 7 said bulb and offset toward and facing said flattened reflector and electrically connected in series with the front face With its mouth adjacent thereto and of a size fil'st-melltloned filamentclosely approximating that of said front face, a filament NO mferences fled in predetermined relation to said reflector and between said reflector and said front face, current supply and sup- JAMES w LAWRENCE, Primary Examiner port members supporting said reflector and said filament ARTHUR GAUSS, Examiner.

and having portions sealed in and supported from said I stem member, and a ballast filament located behind said DEMEO! Amslam Exammer-

Claims

1. AN ELECTRIC PROJECTION LAMP COMPRISING A GLASS BULB HAVING A MAIN TUBULAR PORTION HAVING A FLATTENED FRONT FACE PORTION AND CLOSED BY A GLASS STEM MEMBER SEALED TO THE END THEREOF, A SEPARATE CONCAVE REFLECTOR WITHIN THE MAIN PORTION OF SAID BULB AND FACING SAID FLATTENED FRONT FACE PORTION WITH ITS MOUTH ADJACENT TO SAID FACE PORTION, A FILAMENT IN PREDETERMINED RELATION TO SAID REFLECTOR AND BETWEEN SAID REFLECTOR AND SAID FLATTENED FACE PORTION OF THE BULB, CURRENT SUPPLY AND SUPPORT MEMBERS SUPPORTING SAID REFLECTOR AND SAID FILAMENT AND HAVING PORTIONS THEREOF SEALED IN AND SUPPORTED FROM SAID STEM MEMBER.