WO2000052737A1

WO2000052737A1 - Incandescent lamp

Info

Publication number: WO2000052737A1
Application number: PCT/US1999/011676
Authority: WO
Inventors: Thomas A. Hough
Original assignee: Vari-Lite, Inc.
Priority date: 1999-03-05
Filing date: 1999-05-26
Publication date: 2000-09-08
Also published as: AU4209899A

Abstract

An incandescent lamp (60) is characterized by a plurality of linear, helically-coiled filaments (21-28) located within a transparent glass bulb (52) having a central longitudinal axis (31) and arranged substantially symmetrically around the central axis (31) such that longitudinal axes of the filaments (21-28) comprise skew lines, which are not parallel and do not intersect each other. This minimizes mutual shadowing of the plural filaments (21-28) to increase the efficiency of an illumination system using the lamp (60) and provide more even distribution of light energy from the lamp (60).

Description

INCANDESCENT LAMP

FIELD OF THE INVENTION

The invention relates generally to incandescent lamps, and especially to lamps adapted for use with a concave reflector for collecting a high proportion of the emitted light and projecting a high-intensity beam with even light distribution.

DESCRIPTION OF RELATED ART

The efficiency of a light collection apparatus in any illumination system depends in part upon the amount of light radiating from a light source that is actually incident upon a light collector, such as a concave reflector. The evenness of light distribution in such a system depends in part upon even distribution of light radiating from the light source towards the light collector. For incandescent lamps having only a single filament, especially a single helically-coiled filament arranged with its longitudinal axis parallel to and coincident with an axis of light beam projection, there is no decrease in efficiency nor evenness of distribution owing to one filament or filament section shadowing another filament or filament section. However, when plural filaments or filament sections are enclosed within a single transparent envelope or glass bulb, there is a tendency for the various filaments or filament sections to obscure or shadow each other, thereby reducing the amount of light energy that radiates from the lamp towards a light collector in certain planes in which the two filaments or filament sections lie, which reduction in light energy radiation contributes to uneven distribution of light in the corresponding illumination system.

Alexander discloses in U.S. Pat. No. 2,592,102, an incandescent lamp having plural filaments arranged in a W form which in front view may be more or less annularly arranged about a central axis of the lamp. Since longitudinal axes of adjacent filaments appear to intersect, any two adjacent filaments must therefore lie in the same plane and will consequently shadow each other. Further, the proximity of the ends of the respective adjacent filaments contributes to excessive heating of the filament wires, which promotes premature failure of the lamp as the filament wires burn out near their respective proximate ends.

Nygorden et al disclose in U.S. Pat. No. 3,364,377, an incandescent lamp having three parallel filaments symmetrically arranged about a central axis.

Although the respective ends of adjacent filaments are no closer together than the nominal separation of the filament coils themselves, thereby avoiding excessive heating thereof, the parallel filaments are each one co-planar with each of the other two filaments, thereby shadowing each other to the detriment of efficiency of light collection and evenness of light distribution.

Cunningham discloses in U.S. Pat. No. 5,268,613, an incandescent lamp characterized by plural filaments that are arranged parallel to each other and also parallel to the axis of light projection of a cooperating concave reflector. The array of filaments, typically four filaments symmetrically arranged in a substantially square-pattern, radiates light generally transversely to the axis of projection where it can be more easily collected. The array of filaments is compact, being no wider transversely than the length of the filaments. Even though the filaments are tightly wound, each filament obscures the other in certain planes in which both filaments lie, thereby causing a lessening of intensity directed in those planes. This lessening of intensity in the planes in which the parallel filaments lie limits the efficiency of the system and contributes to uneven distribution of light from the lamp to the cooperating reflector.

A multi-filament array 1 for an incandescent lamp, as shown in Figure 1, consists of several coils 2-9 suspended between two coaxial mounting circles 10 and 11, connected in series electrically by connecting wires 12-18. The coils 2-9 are symmetrically arranged about a central axis 19, and in accordance with the prior art, arranged parallel to each other and parallel to the central axis. SUMMARY OF THE INVENTION

It is an object of the present invention to provide more even distribution of light from a multi-filament lamp by minimizing the shadowing effect of the plural filaments upon each other.

A further object of the present invention is to provide a light system that converts a maximum of energy input into the lamp into useful light output.

These and other objects are provided by an embodiment of the present invention which includes: a transparent glass bulb having a central longitudinal axis; and a plurality of linear, helically-coiled filaments located within the bulb and arranged substantially symmetrically around the central longitudinal axis such that longitudinal axes of said filaments comprise skew lines, which are not parallel and do not intersect each other.

An additional embodiment of the invention provides an incandescent illumination system including : a concave reflector having a longitudinal axis; and an incandescent lamp including a plurality of linear, helically-coiled filaments located within a transparent glass bulb and arranged substantially symmetrically around the longitudinal axis of the reflector such that longitudinal axes of the filaments comprise skew lines, which are not parallel and do not intersect each other

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of an embodiment of a multi-filament lamp array concept according to the prior art; Figure 2 is a perspective view of an improved lamp array concept according to the present invention;

Figure 3 is a perspective view of a preferred lamp array concept according to the present invention;

Figure 4 is a side view of a multi-filament array apparatus;

Figure 5 is an end view of a multi-filament array apparatus;

Figure 6 is a side view of a multi-filament lamp; Figure 7 is a graph showing distribution of light intensity from a prior art lamp;

Figure 8 is a graph showing distribution of light intensity from a multi- filament lamp according to the present invention;

Figure 9 is a view of an alternate multi-filament array; Figure 10 is a view of another alternate multi-filament array; and

Figure 11 is a side view of a lamp in a concave reflector.

DETAILED DESCRIPTION

The described embodiments of the present invention comprise an incandescent lamp filament containing, for example, six, seven, eight, or nine helically-coiled segments anchored on two circles. Each coil is angled in two orthogonal directions with respect to a central axis of symmetry of the filament array such that longitudinal axes of the various filaments comprise skew lines with respect to the central axis and also with respect to each other. In geometry, two or more lines that have no intersections but are not parallel are called skew lines. Because two lines in a plane must intersect or be parallel, skew lines cannot lie in the same plane. Because the longitudinal axes of the filaments are symmetrically arranged about a central axis such that no filament lies in the same plane with any other filament, the filaments do not shadow each other along the entire lengths of any two filaments. For a given line of sight perpendicular to the central axis of the filament array, one filament will only shadow another filament at a single point.

One embodiment of the present invention consisting of a filament array is shown in Figure 2. Filament array 20, according to the principles of the present invention, comprises eight helically coiled filaments 21-28 of substantially the same length. Filaments 21-28 are suspended between two co-axial circles 29 and 30 of substantially the same diameter, and are arranged symmetrically around central axis 31. Filaments 21-28 are skewed relative to each other and central axis 31 by rotating one of the circles 29 or 30 by 45 degrees about central axis 31. It can be seen from Figure 2 that the filaments 21-28 are disposed at an angle with respect to the central axis 31 and also with respect to each other. Particularly, each filament is inclined in two directions with respect to the central axis 31 because one end of each filament has been revolved through 45 degrees about central axis 31 as a consequence of the rotation of one of mounting circles 29 or 30. Filament array 20 can be fixed in this position for mounting in a lamp.

A preferred embodiment of the present invention is shown in Figure 3. Filament array 40 consists of eight coiled filaments 41-48. Filaments 41-48 are skewed relative to central axis 51 by rotating one of the mounting circles 49 by 90 degrees relative to the other mounting circle 50 about central axis 51. Doing this places one end of each filament 41-48 in a position which is revolved 90 degrees about the central axis. The rotation of filament array 40 is 90 degrees as compared with a rotation of 45 degrees in filament array 20 of Figure 2.

Filament array 40 shown is in a side view in Figure 4. Filament array 40 has an overall length of approximately 15 mm. Mounting circles 49 and 50 have a diameter of approximately 10 mm. The coiled portion of each of the individual filaments 41-48 are approximately 13.5 mm in length and are separated from each other by approximately 2.5 mm at their points of closest approach. Figure 5 is a bottom view of filament array 40.

A further embodiment of the present invention is shown in Figure 6. Lamp 60 includes filament array 40 suspended within a transparent envelope 52. Transparent envelope 52 is preferably a hard, high transparency, durable glass capable of withstanding high temperatures. Transparent envelope 52 is mounted to a standard, ceramic base 53. Two electrodes 54 and 55 extend through ceramic base 53 and are electrically connected to the filament array 40. Electrodes 54 and 55 are designed to provide connection to an electrical power source for the lamp. The lamp may be constructed as a Tungsten-Halogen (i.e. tungsten filament in an inert, halogen-bearing gas) lamp rated for 1000 watts at 120 volts or at some higher or lower voltage. Several examples of known techniques for fabricating Tungsten-Halogen lamps are shown in U.S. Patents No. 4,413,205, 4,743,802 and 5,034,656, which are hereby incorporated by reference.

The improvement in light distribution from a multi-filament array according to the present invention can be shown graphically using a light distribution graph. Figure 7 shows a graph 70 of light distribution in a plane normal to a central axis of a prior art array similar to array 1 of Figure 1 having four filaments 61-64. Filaments 61-64 are arranged substantially parallel to and symmetrically around the central axis of the array. From graph 70 it can been seen that the prior art array produces a distribution of light energy having eight distinct lobes 71-78. The deepest shadows are cast in directions indicated as 90° and 270°, and also in the directions indicated as 0° and 180°, in which light from two of the four filaments is obstructed by two other filaments. Other less deep but still significant shadows are cast in intermediate directions in which one filament obstructs light from another while light from two other filaments is relatively unobstructed. Shadows cast in these directions, in which filaments obstruct light from each other, divide the graph of light distribution into eight distinct lobes of peak light distribution.

Figure 8 shows a graph 80 of light distribution in a plane normal to a central axis of multi-filament array 40 of Figure 3. It can be seen that array 40 produces a distribution of light energy that is devoid of deep shadows and exhibits no distinct lobes of peak light distribution.

While the principles of the present invention have been illustrated with reference to a preferred embodiment having eight filaments or filament sections, it should be recognized that these same principles are applicable to multi-filament arrays having more or fewer filaments or filament sections. For example, Figure 9 shows an array 90 of three filaments or filament sections 91-93. The central axes of filaments 91-93 comprise skew lines, which are not parallel with each other and do not intersect. This structure minimizes the shadowing effect caused by filaments obstructing light from each other. If filaments 91-93 were arranged parallel to the central axis and to each other, shadows would be cast in six directions because the light emitted from each filament would be obstructed by the other two filaments.

Another embodiment of the present invention is shown in Figure 10. Array 100 includes four filaments or filament sections 101-104 arranged symmetrically around a central axis 105. The central axes of the individual filaments 101-104 comprise skew lines relative to each other and to central axis 105. One of the concentric mounting circles 106 is made smaller than the other concentric mounting circle 107 so that the array 100 is also tapered. With a multi-filament array, such as array 40 of Figure 3, which is not tapered, a substantial portion of the light emitted by the filaments radiates radially from and perpendicular to the central longitudinal axis of the array. On the other hand, with a tapered array, such as array 100, the greater portion of the light is emitted at an angle less than 90 degrees from central axis 105 as measured from the end of the smaller mounting circle, mounting circle 106 in this case.

This directionality is further illustrated in Figure 11. Filament array 100 is mounted in lamp 110. Transparent envelope 111 extends into concave reflector 108. Reflector 108 collimates light emitted from lamp 110 as is known in the art. Concave reflector 108 is positioned so that its axis of symmetry is roughly coincidental with the central axis of filament array 100. Tapered filament array 100 tends to aim the direction of maximum intensity forwardly (i.e. toward the opening of concave reflector 108). Of course, reversing the direction of taper will reverse the direction of the light. The angle of radiation θ is less than 90 degrees in the embodiment of Figure 11. This angle is determined by the amount of taper of filament array 100. Other arrangements may also be possible in which the central axes of individual filaments or filament sections of a multi-filament array comprise skew lines such that the various filaments of the array are not parallel yet are symmetrically arranged around a central axis of the array.

At a more forward point (i.e. away from base 110) on reflector 108's inner surface, the angle subtended by the forward and rearward ends of the filament array 100 with respect to that point on the reflector is smaller than it would be at a more rearward point. This is because filament array 100 is closer to the rearward part of the reflector and therefor "appears larger" to such rearward points. Filament array 100 "appears smaller" to more forward points on the reflector 108, with the effect that the spread of light rays reflected from such points is less. This tends to direct more of the light through a downstream aperture, projection gate, or lens, and makes the lamp and reflector combination more efficient in terms of energy collection. Therefore, depending upon the particular geometry of a lamp filament array and a cooperating concave reflector, it may be advantageous to direct more of the light to the forward portions of reflector 108. A tapered filament array such as array 100 achieves this by angling the generated light to the forward portion of the reflector 108, thus increasing the efficiency of the lamp and reflector combination.

Although specific embodiments of the present invention are herein disclosed, they are not to be construed as limiting the scope of the invention. Many modifications and improvements to the described embodiments may be achieved by those skilled in the art in light of the teaching of this specification. For example, although a described embodiment provides lamps of the Tungsten Halogen type, any illumination technique using filaments is within the purview of the present invention. For example, a standard evacuated incandescent bulb may be used for lower output applications. Also, although only filament array 110 is shown in conjunction with a concave reflector, any of the disclosed filament arrays may be used with a concave reflector. In addition, the scope of the embodiments of the invention is not limited to the use of concave reflectors. Many other reflector configurations known in the art may be advantageously used. The scope of the invention is only limited by the claims appended hereto.

Claims

THE CLAIMS

We claim: 1. An incandescent lamp comprising: a transparent bulb having a central longitudinal axis; a plurality of linear filaments located within said bulb and arranged substantially symmetrically around said central longitudinal axis such that longitudinal axes of said filaments comprise skew lines.

2. An incandescent lamp as in Claim 1 wherein an array of said linear filaments is tapered towards one end thereof.

3. An incandescent lamp as in Claim 1 wherein said plurality of linear filaments arranged such that said longitudinal axes of said filaments are inclined in two directions with respect to said central longitudinal axis.

4. An incandescent lamp as in Claim 1 wherein said filaments are helically coiled.

5. An incandescent lamp as in Claim 1 wherein said filaments comprise Tungsten.

6. An incandescent lamp as in Claim 1 further comprising a gas sealed in said transparent glass bulb including a halogen bearing species.

7. An incandescent lamp as in Claim 1 wherein said plurality of filaments comprises eight filaments.

8. An incandescent lamp as in Claim 1 further comprising a reflector positioned so that an axis of symmetry of said reflector is substantially coincidental with said central longitudinal axis.

. An incandescent lamp as in Claim 1, further comprising: a base providing support for said plurality of linear helically-coiled filaments and forming a hermetic seal with said transparent glass bulb; and a gas sealed within said transparent glass bulb.

10. An incandescent lamp as in Claim 8 wherein said filaments comprise Tungsten and said gas comprises an inert gas combined with a halogen source gas.

11. An incandescent illumination system for projecting a beam of light, comprising: a concave reflector having a longitudinal axis; and an incandescent lamp including a plurality of linear, helically- coiled filaments located within a transparent glass bulb and arranged substantially symmetrically around said longitudinal axis such that longitudinal axes of said filaments comprise skew lines, which are not parallel and do not intersect each other.

12. An incandescent illumination system as defined in Claim 10, wherein an array of said linear, helically-coiled filaments is tapered towards one end thereof.

13. An incandescent illumination system as defined in Claim 10 wherein said filaments comprise Tungsten.

14. An incandescent illumination system as defined in Claim 10 further comprising a gas sealed in said transparent glass bulb including a halogen bearing species.

15. An incandescent illumination system as defined in Claim 10 wherein said plurality of filaments comprises eight filaments.

16. An incandescent illumination system as defined in Claim 10 wherein the axis of symmetry of said reflector is substantially coincidental with said central longitudinal axis.

17. A method for forming an incandescent lamp comprising: forming a transparent bulb having a central longitudinal axis; and forming a plurality of linear filaments located within said bulb and arranged substantially symmetrically around said central longitudinal axis such that longitudinal axes of said filaments comprise skew lines.