GB2079435A

GB2079435A - Reflector lamp

Info

Publication number: GB2079435A
Application number: GB8117852A
Authority: GB
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1980-07-03
Filing date: 1981-06-10
Publication date: 1982-01-20
Also published as: GB2079435B; CA1172682A; DE3125168A1; JPS5730801A; DE3125168C2; FR2486200A1

Abstract

A reflector lamp comprising a concave reflector 11 having a parabolic rear section 15, a spherical intermediate section, and a parabolic front section 12, each of the reflector sections having the same common focal point 13, and a light source 16 at the common focal point, the reflector sections being dimensioned so that all light rays from the light source which are reflected by the spherical intermediate section become re-reflected by the parabolic front section. <IMAGE>

Description

SPECIFICATION Reflector lamp The invention is in the field of optical reflectors and reflector lamps.

One general type of reflector lamp comprises a concave reflector having a parabolic contour with respect to a focal point, so as to reflect frontwardly light emitted by a light source located at the focal point. The cross-section of the reflector usually is circular, the diameter thereof varying with the distance from the focal point. Additionally, a cone of light rays directly from the light source at the focal point pass, unreflected, through the front of the reflector, the angle of this cone of rays being determined and defined by the front rim of the reflector. The more widely divergent light rays of the cone of rays, i.e. the rays passing relatively nearer to the rim of the reflector, have such a large sideways component of direction so as to fall outside of the deisred light pattern and therefore are wasted.This waste of light can be reduced, and the optical efficiency improved, by making the reflector deeper (longer) so that relatively more of the light is reflected in the desired direction and the cone of non-reflected light is narrower thus reducing the amount of wasted divergent light. However, there are practical limitations on increasing the depth of the reflector, such as cost, weight and awkwardness of using it. Also, with a given maximum diameter as the reflector is made deeper, the focal point moves closer to the rear surface, which complicates positioning of the light source and if the light source is a filament there is accelerated blackening of the nearby rear area of the reflector due to evaporation of the filament material (usually tungsten).This accelerated blackening can be alleviated by providing a concave recess at the rear portion of the reflector, which has the drawback of reducing optical efficiency.

Reflectors have been designed having combinations of parabolic and spherical shapes. For example, U.S. patent No. 2,629,046 shows a reflector having a parabolic front section, a spherical intermediate section, and a spherical rear section. U.S.

Patent No. 1,799,711 shows an automobile headlamp reflector having a parabolic front section, a spherical intermediate section, and a parabolic rear section, these sections being tilted with respect to each other so as to have different focal points. Other reflector shapes have been proposed, such as an ellipsoidal reflector lamp as is disclosed in U.S.

Patent No. 4,041,344.

The present invention attempts to provide a reflector, and reflector lamp, having improved optical efficiency which permits a design having lower power consumption, and to achieve this with a reasonably compact lamp.

The invention comprises, briefly and in a preferred embodiment, a reflector, and a lamp having a reflector, which has a parabolic front section, a spherical intermediate section, and a parabolic rear section, each of the reflector sections having the same common focal point, the reflector sections being dimensioned so that all light rays, or substantially all light rays, which are reflected by the spherical intermediate section from a light source positioned at the focal point, are re-reflected by the parabolic front section.

The present invention will be further described, by way of example only, with reference to the accompanying drawings, in which Figure 1 is a front view of a reflector lamp in accordance with the preferred embodiment of the invention.

Figure 2 is a cross section side view taken on the line 2-2 of Figure 1.

A preferred embodiment of the invention, as shown in the drawing, comprises a reflector lamp having a concave reflector 11 shaped to have a front reflector section 12 which has a parabolic contour with respect to a focal point 13, an intermediate reflector section 14 which has a spherical contour with respect to the focal point 13, and a rear reflector section 15 which has a parabolic contour with respect to the focal point 13. The cross-section of the reflector 11 perpendicular to its principal optical axis is circular, as shown in Figure 1. Thus, each of the three reflector sections is defined by a surface of revolution of a parabolic or a circular curve. A filament 16 is centered at the focal point 13 and preferably is located in or near the plane 17 of mutual truncation at the joinder of the front section 12 and intermediate section 14, as shown in the drawing.

Alternative light sources may be employed in place of the filament 16, such as a halogen regenerative-cycle incandescent lamp or an arc discharge lamp. A lens means such as a shaped lens or cover plate 20 may be placed or sealed over the front opening of the reflector 11,to protect the reflecting surface and keep it clean, and/or to modify the light pattern, and is required if the light source is a bare filament 16 in the reflector. The reflector 11 may be made of molded glass, its inner surface being coated with aluminum or silver to provide a reflective surface, and the filament 16 preferably is made of tungsten and is mounted on a pair of lead-in support wires 18,19 of suitable material such as molybdenum.

Light rays which emanate from the light source 16 at the focal point 13 and which strike the parabolic front reflector section 12, will be reflected in a generally frontward direction, as indicated by the light ray path 21. Similarly, light rays emanating from the filament 16 and which strike the parabolic rear reflector section 15, will be reflected generally frontwardly, as indicated by the light ray path 22. A certain relatively small amount of the light eminating from the light source 16 is not reflected by the reflector 11, and undesirably emerges through the front opening of the reflector in a divergant beam pattern, as indicated by the light ray path 23. The relative amount of this light depends on how far frontwardly the reflector extends from the focal point.

In accordance with the invention, the spherical intermediate section 14 is dimensioned with respect to the parabolic front reflector section 12 so that all, or substantially all, of the light emanating from the light source 16 and which strikes the spherical intermediate section 14, will be reflected thereby in a direction so as strike the parabolic front section 12 and be re-reflected thereby in a generally frontward by direction. For example, a light ray 26 emanating from the light source 16 at the focal point 13 of the reflector, strikes the intermediate spherical section 14 and is reflected back along its path and through the focal point 13, and strikes the parabolic front reflector section 12 and is directed frontwardly as indicated by the light ray path 27.

A preferred method of designing the reflector, is to first design the front section 12 and then design the contour of the special section 14. Next, a line is drawn from the rim 13, and through the focal point 13, to the contour line of the intermediate section 14; this point of intersection establishes the joinder plane 28 at the rear of the section 14 where it joins the rear section 15. Thus the light ray 26' emanating from the focal point 13 and which strikes the spherical intermediate section 14 at or adjacent to its rear plane 28, will be reflected back along its path and through the focal point 13, and strikes the parabolic front section 12 at or near its front rim 31 and is directed frontwardly as indicated at 27'.

In scientific optical terminology, the breadth of the parabolic reflector curve at the focal point 13 is the latus rectum and is represented in the drawing by the line 17 in Figure 2, and the vertex is the point on the rear surface directly behind the focal point 13.

The vertex of the front parabolic section 12 is the point thereon that would be directly behind the focal point 13 if the parabolic curvature were to be continued behind the focal point 13. Thus the focal point 13 is relatively close to the vertex of the front parabolic curve and is substantially farther from the vertex of the rear parabolic curve 15. The diameter of the spherical intermediate section 14 is essentially equal to the length of the latus rectum of the front parabolic curve 12.

Due to the elongated shape of the filament 16, not all the light from different parts of the filament is emitted at the focal point 13, and therefore, will be reflected at slightly different angles at any specific point of the reflector. As a consequence not all of the reflected light from the intermediate section 14 will pass through the focal point 13. Therefore the optical performance of the reflector will be somewhat degraded from that which would be obtained from a hypothetical point source at the focal point 13. In addition, the beam coming from the reflector may, as is the state of the art for such lamps, be further modified by lenses and/or diffusers to achieve a light distribution at some distance from the lamp to meet the requirements for a spot lamp or a flood lamp as commonly conceived by the lighting industry.It will remain true, however, that the major portion of the advantages achieved with the above described re flectorwith regards to a point source will be realized with such an elongated filament and with the customary lenses and/or means of light diffusion.

The space defined and surrounded by the spherical intermediate section 14 provides a recess for accommodating the light source 16, and spaces the reflecting surfaces at the back part of the reflector sufficiently far way from the filament 16 to minimize blackening thereof by evaporated filament material, and the invention accomplishes this while retaining an optical efficiency substantially as good as if the entire reflector had a single parabolic curvature.

Since the invention provides a reflector construction in which all of the light reflected by the intermediate section is re-reflected in the desired frontward direction by the parabolic front section, and is not "lost" by passing beyond the front face in a divergent pattern, the improved optical efficiency permits construction of a lamp requiring lower watts of power for a given amount of useful light, thus contributing to the nation's goals of fuel economy.

Claims

1. A concave reflector shaped to provide a parabolic front section, a spherical intermediate section, and a parabolic rear section, each of said sections having a same common focal point and being dimensioned so that substantially all light rays which are reflected by said spherical intermediate section from a light source positioned at said focal point are re-reflected by said parabolic front section.

2. A reflector as claimed in Claim 1, in which said parabolic front section has a depth such that light rays reflected adjacent to the rear of said spherical intermediate section are re-reflected by the reflector surface adjacent to the front rim of said parabolic front section.

3. A reflector as claimed in Claim 1 or Claim 2, in which said focal point lies in or near a plane defined by the mutual truncation at the joinder of said front section and said intermediate section.

4. A lamp comprising the reflector of any one of claims 1 to 3 and including a light source centered at said focal joint.

5. A lamp comprising a concave reflector having a front section defined by the surface of revolution of a first parabolic curve whose focal point is relatively close to its vertex with the surface terminating essentially at its latus rectum, an intermediate section of spherical configuration having its center at the focal point of said front section and a diameter essentially equal to the length of said latus rectum, and a rear section defined by a surface of revolution of a second parabolic curve whose focal point is substantially farther from its vertex than said first parabolic curve with said two focal points being substantially coincident, said rear section terminating at the circular junction with said spherical intermediate section so that a ray from said focal point to any point along said circularjunction will reflected to the remote edge of said front section, lens means attached to the remote edge of said front section, and a light source located essentially at said coincident focal point

6. A lamp as claimed in Claim 5, in which said light source comprises an elongated filament lying substantially in the plane of said latus rectum.

7. A reflector as claimed in Claim 1, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.