Par Spot Lamp

The present invention relates in general to an improved spot lamp, and in particular to an improved spot lamp of the PAR variety. Even more particularly, the invention is concerned with an improved lamp lens and reflector construction having, inter alia, an overall increased light output efficiency and improved beam candlepower. The available luminous flux from the lamp's source is utilized in a more efficient manner.

It is well known in the art to utilize PAR (parabolic aluminized reflector) lamps for general spot lighting applications. In particular, PAR 38 (those with a 4.75 inch face diameter) spot lamps have become exceptionally popular for short-to-medium-distance outdoor uses as well as indoors for display, decoration, accent, inspection, and downlighting applications. Examples of such spot lamps are manufactured and sold by the assignee of the instant invention under the product designations 75 PAR/SP, 150 PAR/SP, and 150 PAR/3SP. Typically, these lamps are of hardglass and include a medium skirt (screw-type) or side prong base at the rear thereof for connecting the lamp to the desired power source.

The beam produced by a PAR lamp is typically of substantially conical configuration and provides a substantially round pattern. This pattern changes to being oval or elliptical should the lamp be aimed at an acute angle with the light-receiving surface. These lamps also may possess a rated average life of from 2000 to 4000 hours (with many more recently introduced models exceeding this), operate readily from standard household current (120 volt) and produce a beam having an output typically ranging from about 700 to about 3300 lumens.

Prior spot lamps, such as those of the type PAR 38 variety, include a lens that has either a stippled or irregular lens surface typically obtained by shot or sand blasting. The stippled surface usually appears over substantially the total face of the lamp lens. The resultant light pattern from such a surface provides a generally undesired asymmetrical pattern which is a function substantially solely of the stipple density. Moreover, a further drawback of existing spot lamps of this type is that there is little or no control of the beam pattern.

In addition to the aforementioned drawbacks associated with the spot lamp lens, there are further problems associated with the spot lamp reflector. Prior spot lamps such as type PAR 38 spot lamps utilize a reflector having a multiple parabolic front (forward) section generated by the combination of three different radii portions, a middle section formed of a partial sphere and a heel or rear section that is also of a partial sphere. This prior art construction of a reflector, particularly when taken in combination with the described stippled lens, provides a relatively inefficient means of projecting the available light. This arrangement further provides a narrow latitude for beam pattern alteration and also an undesired, asymmetrical candlepower distribution.

It is an object of the present invention to provide a spot lamp having an improved reflector and lens construction for providing enhanced light output efficiency and an increased beam candlepower leading to a savings in lamp operating cost.

Another object of the present invention is to provide an improved spot lamp construction as in the foregoing object and which further provides improved control of the resulting beam pattern.

In accordance with the present invention, there is provided an improved spot lamp having enhanced light output efficiency and beam candlepower, along with improved control of beam pattern. The improvement in the operating parameters of the spot lamp is due to both improvements in lens and reflector construction. In accordance with one aspect of the invention there is provided a lens having a series of concentrically disposed fluted rings on the lens surface each having a progressively increased radius, along with an outer concentric ring portion adjacent to and wider than one of the fluted rings. This outer concentric ring portion includes a stippled surface. By combining fluted concentric rings having specified radii with different stipple densities, a more controllable, symmetrical, and pleasing (softer) spot beam pattern is realized. The lamp's candlepower distribution may be readily varied to many different shapes by altering such factors as the number of fluted rings, the ring flute radii, ring location and stipple density.

FIG. 1 is a cross-sectional, side elevation view of a spot lamp constructed in accordance with the principles of this invention;

FIG. 2 is an elevational view of the first (internal) surface of the lens member of the invention as taken along the line 2--2 in FIG. 1;

FIGS. 3A, 3B, and 3C are fragmentary views of a circular segment of the lens first surface showing different stipple densities;

FIGS. 4A, 4B, and 4C are fragmentary cross-sectional views showing different specific forms of the concentric fluted rings; and

FIG. 5 is a graph of candlepower versus degrees (from lamp axis) showing a series of candlepower distribution curves for different ring and stipple combinations.

For a better understanding of the present invention together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above described drawings.

With regard to the drawings, and in particular FIGS. 1 and 2, there is shown a PAR-type spot lamp that generally comprises a reflector portion 10, a lens member 20, and a light source 30. The source 30 may be either a single incandescent (e.g., tungsten) filament or, alternatively, may be a pressurized halogen capsule. Light source 30 is disposed within and, therefore, substantially surrounded by reflector portion 10. In accordance with the invention, an optically improved reflector portion construction is combined with the curved spot lamp lens member 20 having both a concentric, fluted ring portion and a concentric ring portion of stipple construction, whereby the combination provides a more accurate and uniform beam pattern. In addition to the reflector and lens, FIG. 1 also illustrates the metallic (e.g., aluminum) screw-in base 35 which is of conventional construction. Both the reflector and lens components of the invention are of hardglass material.

The reflector 10 illustrated in the drawings represents an improvement over previous PAR reflector designs by providing improved optical characteristics, yet without significantly changing the outer size or contour to any great extent so that the lamp remains compatible with any lamp fixtures presently used. Previously, the front (forward) section of the reflector (that adjacent the curved lens) was formed by a series of different diameter spherical segments. Furthermore, there was no interrelationship between the radii of the different segments of the front section and the radius of the middle section of the reflector.

Now, as illustrated in FIGS. 1 and 2, in accordance with the present invention, the reflector is provided with a first (front) section 12 which is now in the form of a true parabolic surface 13, thus producing a greater number of parallel rays when the light source 30 is located at the principle focus 32 of parabolic surface 13. FIG. 1 illustrates the rays R1 emanating from the source 30 and reflected at the parabolic surface 13 through the curved lens 20.

In addition to first, parabolic section 12, reflector 10 also comprises a second reflective section (14), said section being of substantially spherical configuration. The radius of the spherical surface 15 of second section 14 is taken at the principle focus point 32 so that the center of the radius of this (second) section coincides with the principle focus point of parabolic surface 13. It is further noted that FIG. 1 illustrates the rays R2 emanating from source 30 and reflecting off surface 15. These rays then pass essentially back through the source 30 and are eventually reflected from the parabolic surface 13 of the first section.

Reflector 10 also includes a rear or heel (third) section 16 through which wiring extends in a conventional manner for providing electrical connection between base 35 and the light source 30. The rear section 16 has an inner, substantially spherical reflective surface 17 which may have a radius substantially the same as conventional prior lamps. In the instant invention, the radius of the third reflective surface is greater than that of the spherical second surface. In one embodiment, the parabolic front section 12 of the reflector may have a focal point of about 0.49 inch, and the radius of curvature of the middle, spherical section 14 may be about 0.86 inch. The radius of the rear section 16 in turn may be about 2.40 inch.

The inner reflective surfaces of reflector 10 may be constructed relatively smoothly throughout the different sections in which case the reflector remains "plane specular". Alternatively, this inner surface of the reflector throughout the different sections may be stippled by shot blasting various areas to provide a "diffuse specular" reflective surface.

As indicated previously, prior spot lamps utilized a lens that had a totally stippled external lens surface usually obtained by shot or sand blasting. The resultant light pattern from such a surface provided a generally asymmetrical pattern which was a function solely of the stippled density. Furthermore, there was no real control of the resulting beam pattern. However, in accordance with the present invention, there is now provided a combination of a reflector having at least three different reflective segments with an adjacent lens member of curved configuration having a first, inner surface comprised of fluted concentric rings 22 in combination with an outer concentric ring portion 24 of stippled construction, said outer ring portion adjacent to and generally wider than any one of the inner, fluted rings. As illustrated, for example in FIG. 2, it is noted that the lens, when viewed in elevation, has a generally circular shape and is slightly cupped (see FIG. 1). In addition to the several concentric fluted rings 22 and stippled concentric area 24, there is also provided a substantially circular central portion 26 which may be left plain (not fluted), but is preferably also stippled (FIG. 2). In FIG. 2, the area 26 is shown as having a medium density stipple while the outer ring 24 is shown having a lighter density stipple. Furthermore, in the embodiment of FIG. 2 there are employed a total of four concentrically disposed fluted rings 22 on the first, inner surface of the lens. In other embodiments, different numbers of rings may be employed. For example, in FIG. 5 to be referred to hereinafter, the graph illustrated therein shows the use of different numbers of rings, including six and seven rings, and in one embodiment, where all rings are employed. This would provide for a total on the order of 12-15 rings for a typical PAR 38-type lamp (outer diameter of about 4.75 inch).

With the use of a combination of fluted concentric rings and the stippled outer ring portion, there has been provided a more controllable, symmetrical, and pleasing (softer) spot beam pattern. Furthermore, the candlepower distribution of the lamp (maximum center beam and/or spread) may be varied to many desired shapes by altering such factors as the number of rings, the ring flute radii, ring location, stippled density or any number of combined changes. An increase in lumen efficiency is also realized by using fluted rings which provide a better transmission control having a definite geometric relation to the reflector's incident light.

In one example, the lens employed seven concentric rings on the inner surface of the lens with the outer ring portion having a medium stipple. This particular combination provides a beam pattern with a relatively high candlepower intensity in its center (analogous to a spot lamp) and with a narrow spot spread. In all of the aforementioned examples of various fluted ring and stippled area combinations, it is understood that these lens components are located on the internal (first) surface of the curved (non-linear) lens member. The outer, or second, surface of the lens understandably runs parallel to the first surface and is smooth. A smooth outer surface is highly desirable in that it eliminates dust, dirt, etc. build-up as typically occurs in PAR spot lamps having lens elements in the outer surface. Accordingly, the lens elements of the instant invention face the light source and thereby perform their refractive functions prior to the altered light beams passing through the remaining thickness of the glass lens.

As also shown in FIGS. 1 and 2, lens member 20 is oriented such that the lamp axis LA--LA passes through the center thereof. This axis also passes through the midpoint of non-fluted, central portion 26. Regarding FIG. 2, this arrangement is such that the fluted rings are concentrically disposed about central portion 26 (and, therefore, axis LA--LA) each at an increasing radius (the outermost, contiguous to ring portion 24, being at the greater radius while the innermost, contiguous to the central portion 26, is at the smallest radius). Central portion 26, as shown, is of circular configuration.

FIGS. 3A, 3B, and 3C illustrate different stipple densities which may be employed for lens portions 24 and 26. FIG. 3A shows a light stipple, FIG. 3B illustrates a medium (more concentrated) stipple, and FIG. 3C shows a heavy (most concentrated of the three) stipple. The application of the stipple may be in any conventional manner, including that described previously.

FIGS. 4A, 4B, and 4C illustrate fragmentary sections through the fluted ring portion 24 of lens 20, illustrating fluted ring patterns which provide varying amount of spread for the resulting beam. FIG. 4A shows a flute pattern capable of providing wide spread, while FIG. 4B shows a narrow spread flute pattern. FIG. 4C shows a special fluted ring portion where each of the flutes are slightly skewed in comparison to the other fluted rings shown herein.

FIG. 5 is a graph of candlepower versus degrees for a limited number of lamps constructed in accordance with the principles of the invention, which clearly indicates the feature of the invention having to do with the control over resulting beam pattern by use of various combinations of rings and stipples. Curve A represents an embodiment employing six concentric rings and a light stipple for both outer and inner portions 24 and 26, respectively. Curve B illustrates an embodiment in which there are six concentric rings, but instead a medium density stipple is employed for both stippled portions. Curve C also is one employing a medium density stipple, but having instead of six rings, seven fluted rings are utilized. Finally, curve D shows the candlepower distribution in an embodiment employing substantially all fluted rings on the internal surface of lens member 20. As indicated previously, this may have on the order of twelve to fifteen rings. Such an embodiment may provide a central portion 26 (as in FIG. 2) or the rings may run substantially from the very center (axis LA--LA) of the lens to the outer edges thereof.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.