SPECIFICATIONReflector lamp with shaped reflector and lensThe invention is in the field of reflector lamps, such as flood lights and spot lights, having reflectors and lenses. In such lamps, the light source is deeply recessed in a concave reflector which reflects frontwardly in a desired beam pattern substantially more than half of the total light output of the lamp.
U.K. Patent Specification No. 2079435A discloses a reflector lamp having a concave reflector comprising parabolical and spherical sections, for projecting a pattern of parallel light - rays in a frontward direction.
In the use of a concave reflector lamp, there is an undesirably wasted amount of light which emanates from the light source and is not reflected but radiates in a divergent cone pattern through the front of the reflector.
Objects of the invention are to attempt to provide a reflector lamp, combined with a lens, 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 lamp having a concave reflector, which may have one or more parabolic sections, for reflecting light frontwardly from a light source located at the focal point. The light source is deeply recessed in the reflector so as to be at least three times as far from the front opening of the reflector as from the reflector's vertex or virtual vertex, so that substantially more than half of the total light is reflected by the reflector. A lens is positioned over the front of the reflector and is contoured at least near the outer edge thereof to refract frontwardly at least some of the non-reflected divergent light emanating directly from the light source.For a flood light, substantially the entire lens is contoured to refract and converge light rays including the reflected light rays, so that the reflected light rays converge into a cross-over pattern to provide a flood beam pattern.
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 a preferred embodiment of the invention.
Figure 2 is a cross section side view taken on the line 2-2 of Figure 1.
Figure 3 is a side view of the lamp and a flood light beam pattern.
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 1 5 which has a parabolic contour with respect to the focal point 1 3. 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 preferrably is located in or near the plane 1 7 of mutual truncation at the joinder of the front section 1 2 and intermediate section 14, as shown in the drawing.
To achieve the maximum practical optical efficiency, reflector lamps are designed to have the reflector 11 as deep as is feasible, to provide a large area of the primary reflecting surface 12 for reflecting substantially more than half of the total light into the desired beam pattern and so that substantially less than half of the total amount of light emanates directly and unreflected from the light source 1 6 through the front of the reflector in a divergent pattern whereby some of the light is wasted because it falls outside of the desired beam pattern.Thus, the light source 1 6 is deeply recessed in the reflector and is typically at least three times the distance from the front plane or rim 31 of the reflector than from the vertex, or virtual vertex 12' in the embodiment shown, of the primary reflecting surface 1 2. The desired long depth of the reflector is limited by practical considerations such as not wanting unduly great size, weight, bulk, and cost of the reflector.
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 shaped lens 20 is placed or sealed over the front opening of the reflector 11, primarily to modify the light pattern, will be described, and also to protect the reflecting surface and keep it clean, and a cover or lens 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 1 6 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 paths 21. Similarly, light rays 22 emanating from the filament 1 6 and which strike the parabolic rear reflector section 15, will be reflected generally frontwardly.
As is disclosed and claimed in the copending patent appiication No. 2079435A, the spherical intermediate section 1 4 is dimensioned with respect to the parabolic front reflector section 1 2 so that all, or substantially all, of the light emanating from the light source 1 6 and which strikes the spherical intermediate section 14, will be reflected thereby in a direction so as to strike the parabolic front section 1 2 and be re-reflected thereby in a generally frontward direction.For example, a light ray 26 emanating from the light source 1 6 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 previously mentioned the light ray path 21.
A preferred method of designing the reflector, is to first design the front section 1 2 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 1 5. Thus the light ray 32 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 32'. Another such light ray 32, 32' is shown at the opposite side of the reflector.
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 1 3 is relatively close to the vertex of the front parabolic curve 12 and is substantially farther from the vertex of the rear parabolic curve 1 5. The diameter of the spherical intermediate section 14 is essentially equal to the length of the latus rectum 1 7 of the front parabolic curve 12.
Due to the elongated shape of the filament 1 6, 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.
The space defined and surrounded by the spherical intermediate section 14 provides a recess for accommodating the light source 1 6, and spaces the reflecting surface at the back part of the reflector sufficiently far way from the filament 1 6 to minimize blackening thereof by evaporated filament material, and accomplishes this while retaining an optical efficiency substantially as good as if the entire reflector had -a single parabolic curvature.
Some of the light emanting from the source 16 is not reflected by the reflector 11, and emerges from the source 1 6 in a diverging cone-shaped beam, illustrated by the cone edge pairs of light rays 33. Another illustrative pair of diverging light rays 34 within the aforesaid cone-shaped beam, are also shown. This cone-shaped beam, including the cone edge-defining rays 33 and all other rays such as rays 34 contained therein would, but for the lens 20, emerge through the front of the reflector 11 in straight continuation rays 33', 34'.
All of the light rays of the cone-shaped beam, except for those on the optical axis, are divergent and inconsistent with the desired frontward parallel ray pattern provided by the reflector 11, and (but for the lens 20) will fall outside the desired beam pattern and will be wasted light in most applications. The closer the cone rays are to the edge defining rays 33, the more divergent they will be, these edge rays 33 being the most divergent and other cone rays such as rays 34 which are slightly within the cone edge rays 33 being only slightly less divergent.
The light rays 21, 32, 33 and 34 are shown as pairs thereof symmetrically arranged about the optical axis of the reflector 11 , to better illustrate the light distribution patterns in the crosssectional view of Fig. 2 and to facilitate iliustration in Fig. 3 of a projected flood light beam pattern.
In accordance with the present invention, the lens 20 is contoured, at least near its outer rim, to refract in a more frontward direction at least some of the divergent "stray" light rays from the light source, and the lens may be further contoured to provide a flood light beam pattern. The preferred contouring of the lens is in the form of concentric prisms 36, preferably on its inner surface, of theFresnel lens typeIn Fig. 2, the dashed-line light ray representations 21, 32,33, etc. represent light rays from the source 1 6, both reflected and nonreflected within the reflector 11, and the dashedline representations indicated by primed numbers 21 32', 33', etc. of these light rays in front of the light unit indicate what the ray patterns and directions would be without the presence of the lens 20. The solid-line representations, indicated by double-primed numbers 21", 32", 33", etc. of these light rays in front of the lens 20 indicate their patterns, and directions as modified by the functioning of the lens in accordance with the invention.
In accordance with the first-mentioned embodiment of the invention, the concentric prisms 36 are provided on the inner surface of the lens 20 and only near the outer periphery thereof, for example in an outer region of the lens so as to intercept all of the divergent light rays between and including the rays 33 and 34. These prisms 36 are shaped to be optically convergent, so as to refract the divergent light rays 33, 34 and the divergent rays therebetween, in a more frontward direction as indicated by the solid-line rays 33" and 34", and thus more nearly into the desired useful overall beam pattern. At the same time, the reflected and frontwardly directed light rays between and including the rays 21,32 will be converged inwardly by the lens prisms, as indicated by the solid-line rays 21" and 32", and will cross at a region 38 (Fig. 3) in front of the lens 20 and thereafter be divergent and directed somewhat out of the desired beam pattern. Acompromise can be found in the lens design andits degree of optical convergence, so that moreuseful light is gained in the desired overall beampattern by the frontward refraction of theotherwise divergent frays 32', 33' than may be lostdue to the convergent refraction of the otherwiseparallel rays 21 32'. This increases the usefullight output and/or permits the use of a lowerwattage filament 1 6 thus conserving electricalenergy.In this embodiment of providing a lens 20with concentric prisms 36 only near the peripheryof the lens, the reflected and non-reflected lightrays from filament 1 6 which pass through the lenscentral region, such as defined by a circumferencebounded by the light rays 21, are substantiallyunaffected by the lens.
In another embodiment of the invention, a flood lamp having improved electrical and opticalefficiency is achieved by providing the lightrefracting concentric prisms 36 over substantiallythe entire inner surface of the lens 20, as shown inFig. 2. These prisms need not be provided at thereflector's center area 41 where they would berelatively ineffective. Referring again to Fig. 3, inaccordance with the flood light of the invention,the lens 20 refracts the non-reflected divergentlight rays in a more frontwardly divergent pattern,exemplified by the light rays 33" and 34", which is in the desired divergent floodlight beam pattern.
Also, the lens 20 reflects the reflected parallel light beams in a convergent manner to produce a cross-over pattern of rays which thereafter are divergent in the desired flood light pattern. For example, the above-described light rays 21" and 32" cross over at region 38 in front of the lens 20 and thereafter diverge generally in the desired flood light beam pattern. For more completeness,Fig. 3 shows an additional pair of projected light rays 42" and 431r which have been reflected by the reflector 11 toward the lens 20 at an intermediate diameter region 44 thereof and refracted by the lens to converge and cross over at a region 46 in front of the lens and thereafter diverge generally in the desired beam pattern.
Unreflected light rays passing through the lens at its intermediate diameter region 44 will be refracted and projected approximately frontwardly, thus contributing to the overall flood beam illumination. In lamps built according to the invention, the crossover regions 38, 46 lay in the range of about 5 to 20 inches in front of the lens 20.
A unique feature of the invention is the divergent projection of some light rays 33" and 34" and the convergent projection of other light rays 21", 32", 42", and 43" which light rays cross over and become divergent in a manner compatible with the divergent rays 33" and 34" to provide a desired flood light beam pattern. The concentric prisms 36 need not have identical refraction angles; the refraction angles of some or all of the various prisms can be different from one another to tailor the light distribution for uniform intensity or other desired characteristics in theprojected light beam. By thus providing the lens20, in cooperation with the reflector 11, most ofthe projected light rays are in the desired beampattern and relatively little light is wasted, thusimproving efficiency and conserving electricalenergy.