CA1172682A

CA1172682A - Reflector lamp

Info

Publication number: CA1172682A
Application number: CA000381080A
Authority: CA
Inventors: Gilbert H. Reiling; John M. Putz; David D. Van Horn
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1980-07-03
Filing date: 1981-07-03
Publication date: 1984-08-14
Also published as: GB2079435B; JPS5730801A; DE3125168A1; FR2486200A1; GB2079435A; DE3125168C2

Abstract

REFLECTOR LAMP

Abstract of the Disclosure A reflector lamp comprising a concave reflector having a parabolic rear section, a spherical intermediate section, and a parabolic front section, each of the reflector sections having the same common focal point, and a light source 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.

Description

~. 1'7~6~

REFLECTOR LAMP

Background of the Invention The invention is in the field of optical reflectors and reflect~r lamps.

One general type of reflector lamp comprises a concave reflector having a parabolic contour with respect to a focal pointr so as to reflec* 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 Eocal point. Additionally, a cone of light rays directly from the light source at the focal point passr 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 desired 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 re1ected in the desired direction and the cone of non-reflected light is narrower thus ,. .

1 17;~6~12

-2- LD-~237 reducing the amount of wasted divergent light~ However, there are practical limitations on increasing the depth of the re~lector, 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 nearhy 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 diferent focal points~ Other re1ector shapes have been proposed, such as an ellipsoidal reflector lamp as is disclosed in U.S. Patent No. 4,041~344.

Summary of the Invention Objects of the invention are to provide a reflector, and reflector lamp, having improved optical e~ficiency which permits a design having lower power consumption, and to achieve this with a reasonably compact lamp.

`" i l72~

-3- LD-8237 The invention comprises, briefly and in a preferred embodiment, a reflector, and a lamp having a reflector, which has a parabolic fronk 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.

Brief Description of the Drawing .
Fiyure 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.
::
:: Description of the Preferred Embodiment 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 :25 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 deined by a surface of revolution of a parabolic or a circular curve. A filament 16 is centered at the focal point 13 and preferrably 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.

f~

-4- LD-8237 Alternative light sources may be employed ir. place of the filament 16, 5uch as a halogen regenerative-cycle incandescent lamp or an arc discharge lamp. A lens means such as a shaped lens or cover plate ~0 may be placed or sealed over the front opening o~ 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 preferrably is made of tunysten 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 re~lected by the ~ 25 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 aacordance with the inventiont 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 1 1~7~2

-5- LD-8237 the light source 16 at the focal point 13 of the reflector, stri~es 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 spherical section 14. Next, a line is drawn from the rim 31, 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 27l~
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 Fig. 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 ~30 relatively close to the vertex of the front parabolic : :curve and is substantially farther ~rom the ve~tex 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~

6 ~ 2 -6- LD~8237 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 13l and therefore, will be refleccted at slightly different angles at any specific point o 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 adddition, the beam coming from the reflector may, as is the state of the art for such lamps, be further modified by lenses andjor 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 reflector with 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 r and spaces the re~lecting 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 6 ~ ~

-7- LD-8237 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.

Whilè preferred embodiments of the invention have been shown and described, various other embodiments and modiications thereof will become apparent to persons skilled in the art, and will fall within the scope of the invention as defined in the following claims.

.

: ~
~::
:~
, , :

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows-

1. A concave reflector comprising: a parabolic front section, a spherical intermediate section, and a parabolic rear section, said parabolic sections having a common focal point coincident with the center of said spherical section, said spherical section having a diameter essentially equal in length to the latus rectum of said parabolic front section, said sections being dimensioned so that substantially all light rays reflected by said spherical intermediate section from a light source at said focal point are re-reflected by said parabolic front section.

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

3. The reflector of Claim 1, 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 Claim 1, and including a light source centered at said focal point.

5. The lamp of Claim 4, in which said parabolic front section has a depth such that light rays reflected by said spherical intermediate section adjacent to the rear thereof are re-reflected by said parabolic front section adjacent to the front rim thereof.

6. The lamp of Claim 4, in which said light source lies in or near a plane defined by the mutual truncation at the joinder of said front section and said intermediate section.

7. A lamp comprising: a concave reflector having a front section, an intermediate section, and a rear section, said front section being defined by a surface of revolution of a first parabolic curve whose vertex is relatively close to its focal point with the rear edge of said surface being located essentially at its latus rectum, said intermediate section being defined by a spherical surface having its center at the focal point of said front section and having a diameter essentially equal in length to said latus rectum, and said rear section being defined by a surface of revolution of a second parabolic curve whose vertex is substantially farther from its focal point compared with said first parabolic curve, said two parabolic curves having a common focal point, the front edge of said rear section being located at a circular junction with said spherical intermediate section so that a light ray from said focal point to said intermediate section adjacent said circular junction will be reflected by said intermediate section to said front section adjacent the front rim thereof, lens means attached to the front rim of said front section, and a light source centered at said focal point.

8. The lamp of Claim 7, in which said light source comprises an elongated filament lying substantially in the plane of said latus rectum.