LIGHT REFLECTANT SURFACE IN A RECESSED CAVITY SUBSTANTIALLY SURROUNDING A COMPACT FLUORESCENT LAMP

Abstract: The present invention is an improved reflector fo use in a compact fluorescent lamp (CFL) luminaire and a luminaire incorporating such a reflector. The present invention achieves significantly improved light output from a CFL by employing a reflector of expanded polytetrafluoroethylene. Not only is light output improved over presently employed CFL luminaire reflectors, providing more light and/or allowing for less energy usage, but the luminaire of the present invention also produces a more pleasing light output.

Description: TITLE OF THE INVENTION LIGHT REFLECTANT SURFACE IN A RECESSED CAVITY SUBSTANTIALLY SURROUNDING A COMPACT FLUORESCENT LAMP RELATED APPLICATIONS The present application is a continuation-in-part of co-pending United States Patent Applications Serial Nos 08/369,850, filed January 6, 1995, allowed, and 08/630,243, filed April 10, 1996 BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to surfaces used to reflect light, and particularly to highly light reflectant surfaces that provide even diffusion of light for the purpose of maximizing efficiency for recessed compact fluorescent downhghts and the like 2 Description of Related Art The present invention generally relates to the field of lighting, and more particularly to lummaires which utilize a reflector for redirecting light The term "luminaire" as used herein is meant to describe a complete lighting unit comprising a lamp or lamps together with components designed to redirect and distribute light from the lamp(s), along with a housing which positions and protects the lamp(s) and components Lummaires can be categorized by numerous methods Typically, there are indoor and outdoor luminaire applications Indoor lummaires can be categorized by light output emitted above and below the horizontal The Commission Internationale de I'Eclairage (CIE) has various luminaire classifications These are direct, semidirect, general diffuse, semi-indirect, and indirect Direct lighting defines light that is at least 90% below the horizontal Semidirect lighting is predominantly downward at 60-90% of the light below the horizontal General diffuse light describes output where the downward and upward components are about equal Semi-indirect are predominantly upward with 60-90% of the light above the horizontal Indirect lighting describes systems are those where 90-100% of the light is directed toward the ceiling and upper side walls Within these categories, there are many applications Some typical applications include recessed lummaires such as fluorescent troffers, incandescent and compact fluorescent downlighting, and high intensity discharge (HID) downlighting. There are also ceiling-mounted luminaires, track mounted, wall-mounted, suspended, and portable luminaires. Outdoor luminaires can be categorized by similar methods. Light distribution of luminaires is categorized by the Illuminating Engineering Society of North America (IESNA) into five light distribution types. These range from narrow symmetrical distribution to wide non-symmetrical patterns. Some typical applications include pole-mounted luminaires, surface-mounted luminaires, bollard luminaires, and floodlight luminaires. In virtually all of the luminaire applications mentioned above, light is redirected by the use of a reflective material. The reflection characteristics of these materials can be described as being either specular, diffuse, or a combination thereof. While good mirrored surfaces can provide nearly perfect reflectivity of visible light, the light energy exiting these surfaces does so only at an angle equal to the incident angle of light contact. This type of reflection is referred to as specular reflectance. For many applications it is important that light be reflected with an even distribution of light from the surface. This latter property is referred to as diffuse or "lambertian" reflectance. Throughout the years, reflective materials for luminaires have been studied, optimized, and specified. Specular materials are typically used in luminaires which are designed to preferentially deliver focused light to specific locations. Diffuse materials are more typically used for even dispersion of light having uniform characteristics without the undesirable high and low intensity light areas which are typically generated through the use of specular reflectors. This is desirable for many applications such as work and home locations where even lighting is preferred. Various methods of utilizing these type of diffuse reflectors are discussed, for example, in U.S. Patents 5,192,128 and 5,378,965. There are also many designs which use both specular and diffuse materials to take advantage of both types of reflective characteristics, such as in U.S. Patents 5,051 ,878 and 5,075,827. In other applications a diffuse reflector coupled with a fresnel lens is utilized to create a uniform directed beam. This is discussed in U.S. Patent 4,504,889. In still other applications, a diffuse reflector is used in conjunction with diffusers, lenses, or louvers to preferentially direct the light emitting from the luminaire to specific areas. A diffuser scatters the light exiting the luminaire. A lens typically incorporates a series of prisms to preferentially light specific areas of its field of view. A louver is an array of open cells, the walls of which form reflectors. Any of these diffusers, lenses, or louvers can be utilized to redirect light in a wide range of applications, such as 2 x 4 foot fluorescent troffers, compact fluorescent downlights, as well as low and high bay HID warehouse luminaires. Due to the many requirements, the diffuse reflective material choices are relatively few. The most commonly used diffuse reflective materials are diffuse aluminum, white synthetic enamel paint, and white porcelain enamel paint. According to the Illuminating Engineering Society of North America, these three materials exhibit the highest diffuse reflectance through the listed visible wavelengths of 400 nm, 500 nm, and 600 nm. In these wavelengths, diffuse aluminum ranges from 75-84% reflection, white synthetic enamel paint ranges from 48-85% reflection, and white porcelain enamel paint ranges from 56-84% reflection. Under these criteria, these typical diffuse reflective materials have a visible reflectance maximum of only 85%. At this reflectance level, 15% of the light which impinges upon the reflector is not utilized. Furthermore, in many applications which use diffuse reflectors, there can be additional loss of light stemming from the multiple reflections which are inherently created with diffuse reflective materials. Depending upon the design of the luminaire and the reflector geometry, there can be as many as fifteen or more multiple reflections of a ray of light before it exits the luminaire. At each reflection point, there is a cumulative loss of light associated with the reflection efficiency of the material. Thus an increase of reflectance efficiency of only a few percent can yield an overall luminaire output increase of as much as 10% to 20% to 50% or higher. It is further evident that the percent reflection of each material listed varies significantly within its own measured visible wavelengths of 400 nm, 500 nm and 600 nm. This variation can introduce an undesirable color shift between the incident and reflected light. Thus the optimum diffuse reflective material for luminaire applications is one that has consistently high reflectance throughout the visible spectrum. Due to the many different applications that exist for reflectant materials, it is not surprising that there are many different commercially available products with a variety of diffuse reflective properties. Until the present invention, the highest reflectance material known with excellent diffuse reflectivity was that described in United States Patent 4,912,720 and sold under the trademark SPECTRALON by Labsphere, Inc., North Sutton, NH. This material comprises lightly packed granules of polytetrafluoroethylene that has a void volume of about 30 to 50% and is sintered into a relatively hard cohesive block so as to maintain such void volume Using the techniques taught by United States Patent 4,912,720, it is asserted that exceptionally high diffuse visible light reflectance characteristics can be achieved with this material, with reflectance over previously available reflectant material increasing from 97% to better than 99% Despite the reported advantages of SPECTRALON material, it is considered quite deficient in many respects First, this material comprises a relatively hard block of material that must be carefully carved or machined to desired shapes and dimensions Commercially, this material is only available in a maximum size of 30 5 cm x 30 5 cm This severely limits how and where this material can be used and greatly increases the cost of using this material in many applications, especially where large single piece reflectors are desired Therefore, where a pliable material is desired (such as with reflectors for fluorescent troffers), the SPECTRALON material plainly is inadequate Furthermore, the additional machining process provides yet another source for contamination that can be detrimental to its reflective properties Second, the SPECTRALON material is apparently limited, both structurally and in its ability to reflect light, to a relatively thick minimum depth (ι e , a thickness of greater than 4 mm) Again, this serves to limit where and how this material can be used Moreover, this limitation tends needlessly to increase both the amount of material required for a given application as well as the weight of the material required for such application Third, the SPECTRALON material is apparently relatively expensive to manufacture and purchase These costs are only increased by the material's difficulty in processing into the final shape from the hard form (i e , excessive amounts of material may have to be machined away and discarded during production) and its minimum thickness requirements As a result, the SPECTRALON material is too expensive to be used in many applications that might otherwise benefit from its reflective properties Other materials currently used for coating reflective cavities are reflective paints or coatings based on barium sulfate, magnesium oxide, aluminum oxide, titanium oxide, and other white powders One such example is Kodak White Reflectance coating No 6080 which is available from Scientific Imaging Systems of Eastman Kodak Co , Rochester, NY This coating is a specially prepared composition of barium sulfate, binder, and solvent Despite good initial diffuse reflectance, this material maintains its reflectance properties for only a limited period of time (e.g., for only about six months) under normal atmospheric conditions. The material is expected to be stable for even shorter periods of time when exposed to high intensity ultraviolet radiation. Furthermore, application of this coating is extremely laborious requiring 4-8 coats to ensure an adequate thickness for best reflectance. Storage, preparation, and application of the mateπal also requires special care. Even after all of the necessary steps for application, it still does not guarantee uniform results. Accordingly, there is a distinct need for a highly diffuse reflective surface that can be easily handled and installed and provide other distinct advantages over existing reflective surfaces used in luminaires. One particular application which can benefit from a high diffuse reflective surface is that of a recessed compact fluorescent downlight. Compact fluorescent lamps are widely used as an energy efficient substitute for conventional incandescent lamps. In order to provide replacements for incandescent flood lights, a compact fluorescent lamp (CFL) with its required ballast is packaged within a housing or cavity having a reflective surface. One application for such replacement lighting device is within a housing recessed within a ceiling. Another application for this replacement lighting is in architectural track lighting. Another use of a CFL is within a recessed fixture which incorporates its own reflector and ballast. This allows for easy replacement of the CFL without replacement of the ballast and reflector. The problem with such compact fluorescent lamps is that, in contrast to an incandescent lamp which produces light at essentially a point source, the fluorescent lamp is elongated along an axis and emits its light from coated surfaces in a direction perpendicular to its elongated axis. Because of the configuration of recessed lighting fixtures, the elongated axis of the fluorescent lamp tubes is aligned with the direction in which the light rays are to be directed. In other words, the majority of the light emitted from the tube is directed into the recessed reflector, and not directly out of the lamp. Therefore, in order to be useful, as much light as possible must be efficiently reflected by a reflector from an emitted direction, perpendicular to the axis of elongation of the tubes, to a direction aligned with the axis of elongation. Some designs attempt to overcome this problem by mounting the elongated axis perpendicular to the direction in which the light rays are to be directed. This configuration creates a new problem in which a large percentage of the light is directed away from the luminaire aperture which then must be redirected around the lamp(s). Replacement floodlights, as well as all other recessed compact fluorescent applications have traditionally employed the same reflective surface materials and design of incandescent lamps. Such design makes use of the focusing characteristics of a parabolic surface. However, since the characteristics of the fluorescent lamp are different from those of incandescent lamps, such parabolic reflectors are inadequate to meet the needs of recessed compact fluorescent downlights. As a CFL light source becomes further recessed in a reflective cavity such that the lamp becomes more substantially surrounded by the reflective cavity, an increased average number of inter- reflections are required for the light to exit. For each inter-reflection (i.e., light bounce) required, there is a loss of light corresponding to the efficiency of the reflective material. For instance, a reflective material having a reflective efficiency of 96% would lose 4% of the light per bounce compared to a material of 98% reflectance, which loses only 2% of the light per bounce. Thus the 96% reflectant material loses twice as much of the light per bounce as the 98% reflectance material. Therefore, as the depth of the reflective cavity increases, further surrounding the lamp, the number of inter-reflections increases. In this situation, the efficiency of the reflective material becomes increasingly critical to maximize the light output of the system. One such previous attempt to overcome these problems is described in U.S. Patent 5,363,295. This patent describes the use of a specular reflector which has segments that are shaped to individually reflect the light from each of the multiple fluorescent tubes. This design is useful for concentrating the light into a center beam but still suffers from relatively low efficiency of total light output. A light source which is "substantially surrounded" by a reflector defines a category of reflective cavities that has an aperture to depth ratio of equal to or less than 2.0. The equation used to calculate this ratio is defined as: R AD = CA™,, ÷ CD ma χ where: R AD = aperture to depth ratio CA mιn = minimum dimension of cavity aperture CD max = maximum dimension of cavity depth Designs which employ reflective cavities having R AD ratios of 2.0 or less can be greatly enhanced by a highly efficient reflective material; with ratios of less than 1.5, and particularly less than 1.0, are even further benefited. Therefore, for recessed downlighting and track lighting applications which utilize a CFL light source which is substantially surrounded by a reflective cavity there exists a need for highly efficient reflective materials and designs in order to make optimum use of the compact fluorescent lamp as a light source in a recessed cavity. SUMMARY OF THE INVENTION The present invention provides an improved reflector for use in a compact fluorescent lamp (CFL) luminaire. The reflector of the present invention maximizes light efficiency in a reflective recessed cavity, which substantially surrounds the CFL, thus dramatically increasing the light output of the CFL luminaire. The present invention preferably employs a reflectant material of expanded polytetrafluoroethylene (PTFE) comprising polymeric nodes interconnected by fibrils defining a microporous structure. While reflectant materials used in luminaires average about 85% reflectance, the present invention provides reflectance levels of 94% to 99% or more. In fact, the material of the present invention has demonstrated higher diffuse reflectivity than the best diffuse reflective materials presently available for any application. In a CFL, this high reflectance is very beneficial, allowing either markedly increased luminance, or reduced the energy input necessary to maintain the same luminance. This can be accomplished by reducing the wattage and/or the number of lamps in the luminaire. By reducing the energy input, a significant long-term cost savings can be realized. Moreover, the material of the present invention produces an even, diffuse light that is believed superior to any available using current CFL designs. Equally important, the material employed in the present invention demonstrates many other properties that make it particularly desirable for use as a reflectant material for compact fluorescent luminaires. First, the material is highly flexible, allowing easy installation into existing planar and non-planar luminaire reflector designs. Also, the material is easily die cut, allowing a piece to be sized to the appropriate dimensions using clean and efficient methods. Furthermore, the material used in the present invention demonstrates superior reflectant properties even at relatively thin thicknesses such as less than 1 0 mm and even less than 0 1 mm in thickness Another additional advantage of the present invention is that with the diffuse nature of the reflective material within the cavity there is no lens required to diffuse the light emanating from the aperture Furthermore, the white color combined with the high reflectance of the reflective cavity helps the tubes of the compact fluorescent lamp to visually blend into the cavity, thereby improving the appearance of the fixture without the need of a lens The material of the present invention is also very stable over time with respect to a wide range of environmental conditions such as temperature extremes (-268°C to +288°C) This property enables the reflective material of the present invention to be placed in close proximity, and even in contact with, high temperature light sources and other lamp apparatus and heat sources The material of the present invention is chemically inert, withstanding most manufacturing and end use corrosive chemical environments ranging from 0-14 pH Furthermore, the material of the present invention resists change or degradation due to exposure to ultraviolet radiation making it ideally suitable for virtually any indoor or outdoor applications An additional advantage of the present invention is that the base material, expanded PTFE (ePTFE), can provide an excellent gasket suitable for luminaires Thus a one piece reflector and gasket can be provided Furthermore, ePTFE has a very low dielectric property, which makes it a superior electrical insulation material New lamp designs can take advantage of this reflective material to also insulate wiring from the metal parts of the luminaire DESCRIPTION OF THE DRAWINGS The operation of the present invention should become apparent from the following description when considered in conjunction with the accompanying drawings, in which Figure 1A is a three-quarter perspective view of a COBRA-type luminaire incorporating the present invention, Figure 1B is a side elevation view of a COBRA-type luminaire incorporating the present invention, Figure 2 is a scanning electron micrograph (SEM), enlarged 5000 times, showing the surface of a light reflectant material of a commercially available diffuse reflective mateπal; Figure 3 is a SEM, enlarged 5000 times, showing the surface of one embodiment of a light reflectant material of the present invention, Figure 4 is a SEM, enlarged 5000 times, showing the surface of another embodiment of a light reflectant material of the present invention, Figure 5 is a three-quarter isometric view of a reflectant mateπal of the present invention, wherein the flexibility of the material is demonstrated, Figure 6 is a graph plotting the reflectance verses wavelength of a reflectant material of the present invention as compared to commercially available materials, Figure 7 is a graph plotting the reflectance verses wavelength of varying thicknesses of the reflectant material of the present invention as compared to commercially available materials, Figure 8 is a graph plotting the reflectance verses wavelength of various structures of embodiments of the reflectant materials of the present invention, Figure 9 is a graph plotting the reflectance verses wavelength of vaπous thicknesses of the inventive material compared to other luminaire reflective materials, Figure 10 is a side cross-section view of a fluorescent light fixture (luminaire) used to test the effectiveness of the present invention, Figure 11 is bottom plan view of a light permeable cover employing louvers, Figure 12 is a three-quarter isometric view of a fluorescent light fixture employing a light permeable cover in the form of a lens, Figure 13 is a three-quarter isometric view of a fluorescent light fixture employing a light permeable cover in the form of a diffuser sheet, Figure 14 is a graph plotting the data generated in the test of Example 8, and Figure 15 is a graph plotting the date generated in the test of Example 9, Figure 16A is a top plan view of a schematic representation of apparatus used to test luminance as described herein, Figure 16B is a side elevation view of the test apparatus shown in Figure 16A, illustrating a compact fluorescent lamp suspended about an angled illuminance meter mounted on a black diffuse surface, Figure 16C is an enlarged side elevation view of the angled illuminance meter shown in Figure 16B, Figure 17 is a side cross-section view of an inventive replacement compact fluorescent luminaire, Figure 18 is a side cross-section view of an inventive vertical compact fluorescent luminaire, Figure 19 is a side cross-section view of an inventive horizontal compact fluorescent luminaire, and Figure 20 is a side cross-section view of an inventive compact fluorescent track light luminaire DETAILED DESCRIPTION OF THE INVENTION The present invention generally relates to the field of lighting, and more particularly to lummaires which utilize a reflector for redirecting light "Luminaire" is meant to describe a complete lighting unit consisting of a lamp or lamps together with components designed to redirect and distribute light from the lamp(s), along with a housing which positions and protects the lamps and components As the term "light" is used herein, it is intended to include any form of electromagnetic radiation, but especially that in the spectrum of visible light (400 to 700 nm wavelength) and through infrared (IR) light radiation (700 to greater than 2500 nm wavelength) For the present invention involving lummaires, the visible wavelengths are of the primary importance It should be appreciated that the mateπal of the present invention may be tailored to modify reflectance in particular bands of light energy through the use of coatings, fillers, or similar materials A typical luminaire 2, in this case a COBRA-type street lamp luminaire, is illustrated in Figures 1A and 1B The luminaire 2 comprises a housing 4 and one or more light sources 6 A reflector 8 is normally provided to direct light in the desired direction Often a shield, lens or other light permeable cover 9 is also provided to better shield the light source and/or to provide particular characteristics to the light exiting the housing As is explained below, the heart of the present invention is the material of reflector 8 This material has numerous exceptional properties, as well as being as reflective or more reflective than any diffuse light reflective mateπal available before the present invention Prior to the present invention, the best diffuse reflectant material commercially available was sold under the trademark SPECTRALON by Labsphere, Inc., of North Sutton, NH. This material comprises a granular polytetrafluoroethylene material that is lightly packed and then molded into a rigid block. Figure 2 is a scanning electron micrograph (SEM) of a surface of a 1/2 inch (12.7 mm) thick reflectant sheet of SPECTRALON material. While this material provides good reflectivity of visible and near IR light, providing up to about 99% diffuse, "lambertian," reflectance over portions of that spectrum of light, the material has a number of drawbacks that constrain its use. Among the perceived problems with this material are: difficulty in processing due to its rigidity, especially where non-planar reflectant surfaces are required; limited range of effective light reflectance across visible and IR light spectrum; relatively thick minimum thicknesses (i.e., its effective reflectance diminishes at thicknesses of less than about 4 mm); and less than optimum diffuse reflectivity. Despite these deficiencies, this material is considered the present standard by which the diffuse reflectivity of all other materials is measured. The present invention employs a distinctly different material comprising an expanded polytetrafluoroethylene (PTFE), such as that made in accordance with United States Patents 3,953,566, 3,962,153, 4,096,227, 4,187,390, and 4,902,423, all incorporated by reference. This expanded PTFE material comprises a microporous structure of microscopic polymeric fibrils (i.e., thread¬ like elements) interconnecting polymeric nodes (i.e., particles from which fibrils emerge). The structure of a biaxially expanded example of this material is shown in the SEM of Figure 3. This material 10 comprises polymeric nodes 12 and numerous fibrils 14 extending from the nodes 12. As can be seen, numerous microporous voids 16 are provided within the material 10. As the term "expanded PTFE" is used herein, it is intended to include any PTFE material having a node and fibril structure, including in the range from a slightly expanded structure having fibrils extending from relatively large nodes of polymeric or other material, to an extremely expanded structure having fibrils merely intersect with one another at nodal points. Expanded PTFE has a number of important properties that make it particularly suitable as a reflectant surface of the present invention. First, PTFE is a highly inert material that is hydrophobic. Accordingly, the material is resistant to both water and a wide variety of other materials that could damage some other reflectant surfaces. Additionally, by expanding PTFE in the manner taught by United States Patent 3,953,566 to form the node and fibril structure, the material undergoes a significant increase in tensile strength and becomes highly flexible Moreover, while packed granular based PTFE material provides good diffuse reflectant properties, it has been discovered that the node and fibril structure of expanded PTFE provides a much higher diffuse reflectance property A preferred reflectant material of the present invention is made in the following manner A fine powder PTFE resin is blended with a lubricant, such as odorless mineral spirits, until a compound is formed The volume of lubricant used should be sufficient to lubricate primary particles of the PTFE resin so as to minimize the potential of the shearing of the particles prior to extruding The compound is then compressed into a billet and extruded, such as through a ram type extruder, to form a coherent sheet of extrudate A reduction ratio of about 30 1 to 300 1 may be used (i e , reduction ratio = cross- sectional area of extrusion cylinder divided by the cross-sectional area of the extrusion die) For most applications a reduction ratio of 75 1 to 100 1 is preferred The lubricant may then be removed, such as through volatilization, and the dry coherent extrudate sheet is expanded rapidly in at least one direction about 1 1 to 50 times its original length (with about 1 5 to 2 5 times being preferred) Expansion may be accomplished by passing the dry coherent extrudate over a series of rotating heated rollers or heated plates at a temperature of between about 100 and 325°C, such as through the method taught in United States Patent 3,953,566 Alternatively, the extruded sheet may be expanded in the manner described in United States Patent 4,902,423 to Bacino, prior to removal of the lubricant In either case, the material may be further expanded at a ratio of 1 1 1 to 50 1 (with 5 1 to 35 1 being preferred) to form a final microporous sheet Preferably the sheet is biaxially or multi-axially expanded so as to increase its strength in both its longitudinal and transverse directions Finally, the material may be subjected to an amorphous locking step by exposing it to a temperature in excess of 340°C The mateπal of the present invention is preferably made in the form of sheets, which, due to their inherent flexibility, may be formed into a wide variety of other shapes as desired, such as tubes, strips, convex or concave structures, etc Additionally, to address particular applications, the material of the present invention may likewise be extruded or otherwise formed into continuous tubes, rods (i e , cylinders), rectangles, uneven shapes and other structures that may be of interest Sheets made from the above processing steps can be produced in thicknesses ranging from, but not limited to, 0 01 mm to 12 mm Sheets can be subsequently layered upon themselves and subjected to temperatures ranging from about 300°C to 400°C while applying sufficient pressures to bond the layers together It has been determined that by providing a microporous surface of polymeric nodes and fibrils, such as that of expanded PTFE, and particularly one that has been expanded in more than one direction, light is reflected off the node and fibril structure at a very high efficiency rate, with very even diffuse dispersion (i e , diffusion) of the light The SEM of Figure 3 shows expanded PTFE material 10 that has undergone extensive expansion in two different directions This structure exhibits a relatively "fine" structure with fibrils 14 oriented in both x and y directions, and small nodes 12 where the fibrils intersect Still another embodiment of the present invention is shown in the SEM of Figure 4 In this case, the expanded PTFE has been expanded in only the longitudinal direction In this example there is a "coarser" structure characterized by larger nodes 12 and thicker fibrils 14 The fibrils 14 are oriented predominantly in a longitudinal direction As is explained in greater detail below, the present invention demonstrates extremely high diffuse reflectivity When compared to the present reflectant standard of SPECTRALON material, the reflectant material of the present invention exhibited substantially higher diffuse reflectivity Moreover, the reflectivity of the material of the present invention proved to have a number of other dramatically improved properties over the present standard First, the reflectivity of the material remains high across a much wider spectrum of light wavelengths Second, the mateπal of the present invention demonstrates exceptional reflectivity even at much thinner profiles as compared with the existing standard material Third, the mateπal exhibits a very predictable, flat-line reflective response across a wide spectrum of light Another important improvement of the present invention is shown in Figure 5 The reflectant mateπal 10 of the present invention is highly malleable, moldable, and flexible, allowing it to be bent, twisted, curved, or otherwise formed into any suitable shape In this respect, the reflectant mateπal of the present invention is a dramatic improvement over previously available highly reflectant materials, such as SPECTRALON polytetrafluoroethylene reflectant materials that must be carved or machined into desired shapes. With the material of the present invention, a host of different non-planar shapes can be formed with minimal effort. These types of thin, flexible, formable materials having at least 95%, 90%, and even 85% reflectivity should have great value for a range of luminaires. The luminance output is dependent on many factors such as lamp wattage, number of lamps, luminaire design, etc., and careful consideration can be given to determine the level of reflectance required by the reflector. It should also be noted that the material of the present invention may be modified through processing or additional fillers and/or coatings to provide high reflectance in one range of the light spectrum and absorbency in another range of the spectrum. For most luminaire applications it is believed desirable to provide a material with a reflectivity of at least 85% over a range of 400 to 700 nm. The present invention may comprise single or multiple layers of expanded PTFE, or may comprise a laminate of one or more layers of expanded PTFE and a backing support material. Since the expanded PTFE membrane alone tends to be susceptible to stretching and distortion, for some applications it may be preferred that the membrane be mounted to a support layer, such as through lamination to a flexible woven or non-woven material, that will help maintain the shape of the image layer during use. One suitable support layer is applied by applying an adhesive material, such as moisture curable polyurethane or solvated polyurethane, to the expanded PTFE membrane and then applying the adhesive-coated expanded PTFE membrane to a flexible backing material (e.g., polyester, polypropylene, MYLAR®, KEVLAR®, nylon, etc.). The two materials can then be bonded to each other under applied pressure, such as by rolling the material between one or more pairs of nip rollers. With use of a moisture curable polyurethane adhesive to bond an expanded PTFE membrane to a woven fabric, such as nylon. The application of a pressure of about 1150 g per linear meter is sufficient to bond the materials together. The materials are then allowed to moisture cure for a period of about 48 hours before use. In addition, to create complex shapes, an expanded PTFE sheet can be bonded to a rigid support material and then formed as a composite into shapes, such as parabolic or ellipsoidal domes. One suitable method for such forming techniques comprises using vacuum forming devices. Without intending to limit the scope of the present invention, the following examples illustrate how the present invention may be made and used: EXAMPLE 1 A reflectant material of the present invention was prepared in the following manner: A fine powder PTFE resin was combined in a blender with odorless mineral spirits (ISOPAR K available from Exxon Corp.) until a compound was obtained. The volume of mineral spirits used per gram of fine powder PTFE resin was 0.275 cc/gm. The compound was compressed into a billet and extruded through a 1.14 mm gap die attached to a ram type extruder to form a coherent extrudate. A reduction ratio of 47:1 was used. Subsequently, the odorless mineral spirit was volatized and removed, and the dry coherent extrudate was expanded uniaxially in the longitudinal direction 4.0 times its original length by passing the dry coherent extrudate over a series of rotating heated rollers at a temperature of 300°C. The sheet was subsequently subjected to an amorphous locking step by passing the sheet over a series of rotating heated rollers at a temperature of 385°C such that the material was in contact with the rollers for about 12 seconds. This material formed a relatively course expanded structure such as that shown in Figure 4. EXAMPLE 2 Another sheet of the present invention was produced in the same manner as Example 1 except for the following differences: The volume of mineral spirits used per gram of fine powder PTFE resin was 0.297 cc/gm. The compound was compressed into a billet and extruded through a 1.52 mm gap die attached to a ram type extruder to form a coherent extrudate. A reduction ratio of 70:1 was used. Subsequently, the odorless mineral spirit was volatized and removed. Three layers of the dry coherent extrudate were then stacked and expanded uniaxially in the longitudinal direction 4.6 times its original length by passing the dry coherent extrudate over a series of rotating heated rollers at a temperature of 310°C. The sheet was subsequently subjected to an amorphous locking step by passing the sheet over a series of rotating heated rollers at a temperature of 385°C for about 40 seconds. Again, this material formed a relatively course expanded structure such as that shown in Figure 4. EXAMPLE 3 A sheet of the present invention was produced in the following manner: A fine powder PTFE resin was combined with an odorless mineral spirit. The volume of mineral spirits used per gram of fine powder PTFE resin was 0.275 cc/gm. This mixture is aged below room temperature to allow for the mineral spirits to become uniformly distributed within the PTFE fine powder resin. This mixture was compressed into a billet and extruded at approximately 8300 kPa through a 0.71 mm gap die attached to a ram type extruder to form a coherent extrudate. A reduction ratio of 75:1 was used. The extrudate is then rolled down between two metal rolls which were heated to between 30-40°C. The final thickness after roll down was 0.20 mm. The material was transversely expanded at a ratio of 3:1 and then the mineral spirits were removed from the extrudate by heating the mass to 240°C (i.e., a temperature where the mineral spirits were highly volatile). The dried extrudate was transversely expanded at 150°C at a ratio of 3.5:1. After expansion, the sheet was amorphously locked at greater than 340°C and cooled to room temperature. This material forms a relatively fine expanded structure such as that shown in Figure 3. Multiple layers of this sheet material can then be stacked, placed under pressure, and exposed to a temperature of about 360°C for about 30 minutes to bond the layers into a cohesive sheet of virtually any desired thickness. EXAMPLE 4 Layered expanded PTFE material similar to that described in Example 3 above is commercially available from W. L. Gore & Associates, Inc., Elkton, MD, as a sheet gasket material under the trademark GORE-TEX GR® sheet gasketing. This material is available in different thicknesses (i.e., constituting different number of layers formed into cohesive sheets). In order to test the effectiveness of the material of the present invention as compared to commercially available light reflectant materials, various samples of sheet gasketing material were tested as follows: Sample 1 : A composite sheet comprising about 15 layers of expanded PTFE sheets with the following properties: Thickness: 0.5 mm Density: 0.60 g /cc Sample 2: A composite sheet comprising about 25 layers of expanded PTFE sheets with the following properties: Thickness: 1.0 mm Density: 0.57 g /cc Sample 3: A composite sheet comprising about 60 layers of expanded PTFE sheets with the following properties: Thickness: 2.2 mm Density: 0.61 g /cc Sample 4: A composite sheet comprising about 85 layers of expanded PTFE sheets with the following properties: Thickness: 3.4 mm Density: 0.59 g /cc Sample 5: A composite sheet comprising about 150 layers of expanded PTFE sheets with the following properties: Thickness: 6.2 mm Density: 0.51 g /cc Additionally, material similar to that described in Examples 1 and 2, above, is commercially available from W. L. Gore & Associates, Inc., as a gasket tape under the trademark GORE-TEX® gasket tape. Again, this material is available in different thicknesses. Samples of this material were tested as follows: Sample 6: A gasket tape comprising a single layer of relatively course expanded PTFE with the following properties: Thickness: 1.0 mm Density: 0.50 g /cc Sample 7: A gasket tape comprising a single layer of relatively course expanded PTFE with the following properties: Thickness: 3.3 mm Density: 0.66 g /cc Each of Samples 1 through 7 were tested in the following manner to quantify their reflective properties: A 2 inch by 2 inch (51 mm x 51 mm) swatch from each of Samples 1 through 7 was placed in a CARY 5E Spectrophotometer with a Labsphere integrating sphere. The spectral range measured was 175 nm to 2500 nm. Data below 250 nm was not reported due to the unreliability of the standard material below this value. All measurements were made in the double-beam mode with the same working standard in the sphere's reference reflectance port. The reflectance standard used was of SPECTRALON material, Labsphere Serial Number SRS-99-010-8111-A. Photomultiplier detection was used below 800 nm and lead sulfide detection was used above 800 nm. All measurements were normalized with respect to the baseline of the system. This data is then corrected by multiplying it by the correction factors supplied with the reflectance standard. This data was then averaged and plotted. The graph of Figure 6 records the reflectance verses light wavelength of one sample of the present invention as compared with three commercially available reflectant materials. Line 18 is the performance of the material of Sample 5 of the present invention as compared with commercially available reflectant materials SPECTRALON (Line 20), SPECTRAFLECT (Line 22), and INFRAGOLD (Line 24), each available from Labsphere, Inc., North Sutton, NH. These materials are represented by their manufacturer to be some of the highest diffuse reflectant materials available. The data plotted for the commercially available materials was obtained from the technical information catalog published by Labsphere, Inc. As can be seen, at all wavelengths of light tested, the reflectant material of the present invention demonstrated markedly higher reflectivity than the commercially available reflectant materials. Additionally, the material of the present invention retained its reflective properties into much higher wavelengths than the commercial materials. It should be noted here that the reflectivity numbers reported herein are not asserted to show better than complete reflectance of light, but, rather, as demonstrating significantly better reflectance than the present state-of-the-art SPECTRALON reflectant material used as a standard. The graph of Figure 7 records the reflectance verses light wavelength of different thicknesses of inventive material compared to similar thicknesses of SPECTRALON reflective material. Lines 26, 28, 30, and 32 respectively represent the performance of Samples 1 , 2, 3, and 4 of the present invention. By way of comparison, lines 34, 36, and 38 respectively represent the performance of 1.0 mm, 2.0 mm, and 3.0 mm thick samples of SPECTRALON material according to published data from the technical catalog of Labsphere, Inc. Sample 1 was included here even though information is not available for SPECTRALON material at a thickness of 0.5 mm. In all cases the inventive material was substantially higher in reflectivity than SPECTRALON reflectant material of similar thickness. This difference appears to be even more pronounced as the materials decrease in thickness. It should be noted that the 0.5 mm material of the present invention, even though six times thinner than the 3.0 mm SPECTRALON material, demonstrates equal to or higher reflectivity within the visible wavelengths of 400 to 700 nanometers. The graph of Figure 8 records the reflectance verses light wavelength of four samples with similar densities of expanded PTFE material of the present invention. Of the four samples, there are two different thickness levels represented, with a coarse and fine structure material at each level. Lines 40 and 42 represent Samples 6 and 7, respectively, each with a relatively coarse structure characterized by large nodes and thick fibrils. Lines 44 and 46 represent Samples 2 and 4, respectively, each having a relatively fine structure characterized by small nodes and fine fibrils. In like thickness comparisons, the finer structure material demonstrated much higher reflectivity than the coarser structure material at all wavelengths tested. For instance, Sample 2 with a thickness of 1.0 mm was substantially more reflective than Sample 6 with the same thickness of 1.0 mm. EXAMPLE 5 Another layered expanded PTFE material similar to that described in Example 4 was produced: A composite sheet comprising about 7 layers of expanded PTFE sheets with the following properties: Thickness: 0.22 mm Density: 0.60 g /cc EXAMPLE 5A Another layered expanded PTFE material similar to that described in Example 4 was produced: A composite sheet comprising about 45 layers of expanded PTFE sheets with the following properties: Thickness: 1.5 mm Density: 0.58 g /cc EXAMPLE 6 Another layered expanded PTFE material similar to that described in Example 4 was produced: A composite sheet comprising about 3 layers of expanded PTFE sheets with the following properties: Thickness: 0.11 mm Density: 0.60 g /cc EXAMPLE 7 Another layered expanded PTFE material similar to that described in Example 4 was produced: A composite sheet comprising about 2 layers of expanded PTFE sheets with the following properties: Thickness: 0.07 mm Density: 0.60 g /cc The graph of Figure 9 records the reflectance verses light wavelength of different thicknesses of inventive material compared to typical light reflectant materials used in luminaires. Lines 47, 48, 49, 50, and 51 respectively represent the performance of Sample 1 from Example 4 and Examples 5, 6, 7 and 5A of the present invention. By way of comparison, lines 52, 54, and 56 respectively represent the performance of diffuse aluminum, white porcelain enamel, and white synthetic enamel according to published data from the LIGHTING HANDBOOK. 8th edition, Illuminating Engineering Society of North America, page 324 (1993). In all cases the inventive material was substantially higher in reflectivity than all of the typical diffuse reflectant materials used in lummaires It is also important to note that all of the materials of the present invention have relatively flat spectral response across the visible spectrum as compared to the typical luminaire reflectant mateπals A reflectant material having a flat line response reflects all wavelengths equally thus reflecting the true color of the lamp source EXAMPLE 8 A typical recessed fluorescent light fixture is illustrated in Figure 10 This fixture 58 comprises a troffer 60, a light permeable cover 62, a reflector 64, and multiple lights 66a, 66b, 66c, 66d The unit shown has a 2 foot x 4 foot (600 x 1200 mm) troffer 60 and a prismatic lens 62 This type of fixture is commercially available from Cooper Lighting of Eufaula, AL The fixture utilizes four 4100K T8 32 watt fluorescent lamps and electronic ballast with a reflector of diffuse white paint on aluminum Test Method As is illustrated in Figures 11 through 13, a number of other light permeable covers 62 may be used with this type of fixture Figure 11 shows a cover 62 having numerous louvers 68 for directly light in particular directions Figure 12 shows a fixture 58 having a lens cover 70 The lens is provided to improve diffusion of light exiting the fixture Figure 13 shows a fixture 58 employing a diffuser 72 Again, the diffuser serves to provide even distribution of light exiting the fixture A test was conducted using the fluorescent fixture illustrated in Figure 10 The test procedure used is set forth below The luminance of the luminaire was measured by positioning the lamp centered and parallel to a diffuse reflective surface (screen) as recommended by the National Lighting Product Information Program, Specifier Reports. Volume 3, Number 1 The screen material chosen was a 0 5 mm thick piece of the inventive mateπal having dimensions of 152 4 cm x 152 4 cm The luminaire was placed 21 6 cm from the screen A uniform grid of 15 by 15 squares was drawn on the screen yielding 225 total measurement locations A radiometer probe was mounted on a stand so that the end of the probe was positioned 3 5 cm from the screen at a fixed 45 degrees angle from the screen Measurements of each target (the center of each square of the grid) were recorded in Foot Lamberts The probe used was a model number SPL 025Y connected to a model number IL1400 monitor both available from Internationai Light Inc of Newburyport, MA The luminance measurements began 30 minutes after the lamps were energized The reflector of the luminaire was then lined with 0 5 mm thick inventive material made in accordance with Sample 1 of Example 4 Strips of pressure sensitive adhesive were used to hold the inventive lining material in place Measurements were then taken and recorded according to the above described test method In a further test using the ePTFE lined luminaire, one of the two center lamps was removed leaving three of the original four lamps Measurements were again taken and recorded according to the above described test method The data from the above three tests are shown in Tables 1 , 2, and 3, respectively The columns, labeled A through O, correspond to the width of the luminaire while rows 1 through 15 correspond to the length of the luminaire The columns from Tables 2, 3, and 4 were averaged and graphed as shown in Figure 14 Additionally, the total average luminance measurements were calculated for each test The control had an average luminance of 478 foot lamberts The lined four lamp luminaire had an average luminance of 604 foot lamberts, representing an increased overall luminance of 26 4% The lined three lamp luminaire had an average luminance of 490 foot lamberts It is important to note that even when a lamp was removed, the average luminance showed a 2 5% increase over the control Figure 14 represents the averaged columns from each of the three tests It is important to note that for all column averages, both of the lined examples exceeded those of the control Comparing the control test with the ePTFE lined four lamp tests the only difference was the addition of the ePTFE reflective liner Between these two tests, all column averages showed a similar level percentage increase with each column having a luminance increase greater than 20% Thus there was an overall increase in luminance of the luminaire, but there was a minimal effect on the light distribution pattern of the luminaire EXAMPLE 9 A test was conducted to determine luminance output of a Cobra Style Highway luminaire catalog # M2RR15S1N2AMS3099 commercially available from GE Lighting Systems of Hendersonville, NC, with a prismatic lens and 150 watt lamp This luminaire utilized a reflector material of diffuse aluminum The test method from Example 8 was repeated with the Cobra luminaire being 17.8 cm from the screen. The reflector of the luminaire was then lined with 1.0 mm thick inventive material made in accordance with Sample 6 of Example 4. Strips of pressure sensitive adhesive were used to hold the inventive lining material in place. Measurements were then taken and recorded according to the above described test method. The data from the above two tests are shown in Tables 4 and 5, respectively. The columns, labeled A through O, correspond to the width of the luminaire while rows 1 through 9 correspond to the length of the luminaire. The columns from tables 5 and 6 were averaged and graphed as shown in Figure 15. Additionally, the total average luminance measurements were calculated for each test. The control had an average luminance of 639 foot lamberts. The ePTFE lined luminaire had an average luminance of 763 foot lamberts, representing an increased overall luminance of 19.4%. Figure 15 represents the averaged columns from each of the two tests. It is important to note that for this application, the center most columns experienced a large percentage increase in luminance, whereas the outermost columns did not have an increase, with some of these outermost columns showing a small decrease. Thus, there was an overall increase luminance of the luminaire, however in this example the light distribution pattern was modified to enhance the center most region of the lighting area. The above Examples demonstrate that the reflectant material of the present invention performs far better and more consistently as a diffuse reflectant material over a wider spectrum of light than the best diffuse reflectant materials used for luminaires. Table 1 CONTROL - STANDARD WHITE PAINTED ALUMINUM REFLECTOR ( AS PURCHASED) A B I C D I Ξ F G I H I J I < I L M N ι O 1 30 45 68 107 182 229 256 284 271 231 169 112 69 43 32 2 36 56 96 189 341 494 570 566 556 476 332 183 96 58 36 3 42 75 125 271 504 773 888 858 869 753 512 278 133 72 39 4 52 87 150 343 628 974 1124 1082 1116 963 652 343 158 84 45 5 56 99 183 381 718 1107 1265 1210 1262 1100 750 392 174 94 48 6 64 106 189 423 762 1172 1355 1306 1339 1160 790 422 197 101 51 7 60 113 194 451 811 1211 1400 1340 1390 1199 820 437 208 104 48 8 60 111 188 460 835 1237 1429 1370 1405 1215 831 430 206 103 47 9 55 115 194 475 846 1228 1408 1351 1396 1206 829 417 209 101 48 10 45 103 192 432 793 1200 1378 1320 1365 1175 795 430 193 105 43 11 44 92 177 413 770 1130 1307 1260 1296 1118 750 402 186 94 48 12 39 84 157 369 687 1002 1142 1105 1141 1002 676 357 163 89 34 13 33 75 128 285 551 794 922 891 884 772 513 283 135 73 28 14 26 59 103 196 352 502 580 577 568 493 330 193 95 57 24 15 20 42 66 107 189 241 291 289 288 240 172 111 69 42 21 Column Avg 44 84 147 327 598 886 1021 987 1010 874 595 319 153 81 39 Total Avg 478 Table 2 LINED WITH 0.5 MM THICK ePTFE INVENTIVE MATERIAL , A B : C D I E F G I H I J I K L M N ( D 1 38 52 81 124 210 270 324 350 329 282 210 136 84 52 39 2 45 66 112 216 416 623 738 719 717 620 422 231 116 71 46 3 52 87 151 317 635 985 1149 1103 1111 977 660 347 163 92 52 4 64 102 182 418 802 1244 1447 1381 1447 1260 847 438 204 109 63 5 69 115 225 472 908 1411 1627 1568 1625 1426 949 487 219 119 64 6 78 129 226 519 965 1514 1730 1660 1723 1499 1000 519 241 126 67 7 73 134 231 542 1020 1561 1780 1709 1788 1547 1038 546 259 131 69 8 76 132 228 553 1038 1575 1800 1734 1803 1559 1053 544 263 136 73 9 67 138 233 567 1032 1562 1779 1720 1773 1545 1045 522 262 131 75 10 64 130 233 529 986 1518 1735 1668 1718 1493 1000 537 243 132 60 11 56 115 222 506 935 1425 1633 1570 1618 1400 932 485 234 114 59 12 49 104 190 450 839 1246 1426 1386 1415 1232 823 444 209 105 43 13 37 89 161 353 681 988 1151 1100 1099 965 643 366 180 93 41 14 35 78 131 242 448 634 744 741 716 622 424 245 129 76 35 15 31 57 87 136 244 315 396 402 358 305 236 143 91 55 31 Column Avg 56 102 180 396 744 1125 1297 1254 1283 1115 752 399 193 103 54 Total Avg. 604 Table 3 LINED WITH 0.5 MM THICK ePTFE INVENTIVE MATERIAL WITH 1 OF 4 LAMPS REMOVED , A B lr * D I E F G I H I J I K I M N > 0 1 30 41 70 115 188 247 274 283 260 227 163 107 64 42 29 2 36 57 99 204 374 556 633 589 533 450 322 172 88 54 34 3 43 77 135 305 580 874 983 874 872 734 495 263 122 68 38 4 53 91 163 394 737 1109 1227 1086 1095 936 627 326 144 77 45 5 58 103 197 442 838 1255 1394 1244 1236 1050 704 356 156 86 47 6 65 110 207 473 879 1334 1475 1314 1322 1115 748 387 175 92 49 7 60 115 211 501 927 1366 1515 1345 1358 1150 768 406 190 96 49 8 62 108 204 501 949 1387 1535 1357 1375 1160 786 401 188 98 52 9 54 112 204 512 948 1383 1521 1342 1361 1153 775 400 194 97 55 10 56 108 209 478 900 1346 1477 1284 1320 1116 746 400 177 100 47 11 59 97 195 457 863 1263 1410 1241 1243 1052 703 383 179 91 48 12 43 89 166 412 759 1111 1222 1093 1092 933 630 339 156 84 35 13 32 79 141 315 616 882 987 865 864 730 490 271 132 70 29 14 24 60 108 210 381 550 619 571 551 468 318 178 93 57 25 15 24 44 71 116 203 259 305 269 283 236 170 108 68 41 22 Column Avg 47 86 159 362 676 995 1105 984 984 834 563 300 142 77 40 Total Avg. 490 Table 4 CONTROL - COBRA STYLE HIGHWAY LUMINAIRE M N O 1 45 61 67 88 93 105 127 142 152 108 104 87 68 60 37 2 65 93 125 221 263 258 300 420 359 250 260 163 110 80 53 3 82 185 233 490 1039 950 1020 1590 1210 907 940 297 207 157 90 4 93 294 658 1250 1620 1405 1850 3120 2210 1520 1306 934 617 350 90 5 75 188 455 1107 2030 2390 2760 2990 3020 2510 1830 1080 610 260 79 6 55 125 276 617 1111 1680 2750 2300 2360 1510 1060 578 342 177 50 7 43 109 246 495 1121 1660 1710 1650 1550 1370 839 453 252 108 41 8 36 73 167 282 471 461 688 840 599 360 306 206 131 68 29 9 28 47 69 90 179 343 413 413 331 237 140 82 59 44 26 58 131 255 516 881 1028 1291 1496 1310 975 754 431 266 145 55 639 Table 5 LINED WITH 1.0 MM THICK ePTFE INVENTIVE MATERIAL M 1 40 56 64 90 108 122 133 143 141 128 109 91 68 56 33 2 52 76 92 172 237 315 332 369 329 270 253 147 107 77 42 3 57 117 147 274 450 730 982 1057 960 716 494 233 173 119 70 4 65 156 356 604 850 1360 1660 1910 1630 1240 779 507 336 224 79 5 73 155 332 730 1560 2770 3780 3400 3240 2650 1398 698 419 223 87 6 76 146 335 815 1650 2980 4720 4470 3930 2820 1530 762 438 272 79 7 57 139 314 680 1550 2630 3230 3410 2980 2500 1370 729 400 230 56 8 42 100 202 340 600 868 1440 1840 1345 817 562 350 220 149 41 9 49 70 97 141 309 585 769 890 690 485 272 153 100 74 35 Column Avg 57 113 215 427 813 1373 1894 1943 1694 1292 752 408 251 158 58 FotaI Avg. 763 The following Examples demonstrate the use of the inventive material with a compact fluorescent lamp (CFL) light source in a recessed cavity. COMPARATIVE EXAMPLE 10 A 65 watt GE MISER® indoor floodlight R-30 was tested to determine total luminance output according to the following test method: Test Method As shown is Figure 16, a luminaire 74 to be tested was suspended 44.8 cm over the center of a 244 cm square black diffuse horizontal planar surface 76. A T-1H Minolta illuminance meter 78 was positioned on the black diffuse surface so that the detector was 38 cm from the test subject when directly underneath. Measurements were taken in a darkened room at a temperature of 25°C ±1°. Line voltage for the test subject was monitored to assure constant voltage. Data points were measured in foot candles and taken along two perpendicular axes 79a, 79b of the planar surface. Starting from the center point directly underneath the test subject, data was taken at 50.8 mm increments moving out from the center along each axis. A total of 33 data points were taken for each axis. Two different detector angles were utilized to assure the detector was pointed at the test subject. The first three data points from the center along each axis utilized an angle of 15° from horizontal, while the remainder of the data points utilized a 50° angle from horizontal. The two axis of data points were then averaged. Each average value was then used to calculate the total lumens impinging upon each 50.8 mm wide annular ring according to the following formulas: • total lumens per annular ring = [ [ffoooott ccaannddlleess xx ππ xx ((ddiissttaannoce from center(mm)) 2 ]/92,903 • test subject total lumens = ∑total lumens per annular ring The results of this test (lumens) were recorded and shown in Table 6 along with the subjects corresponding R AD .CA mιn , CD-,.,, power input (watts) and calculated efficacy (lumens per watt). EXAMPLE 11 Figure 17 represents a compact fluorescent downlight 80 for use in a range of applications for replacing incandescent downlights, track lights, wall washers, etc. These applications include situations where it is desired to replace existing incandescent units, such as flood lights, spot lights, A-lamps, etc., with a screw-in type fluorescent lamp. There are many types of these screw in type fluorescent lamps currently sold, such as those described in U.S. Patents 5,363,295, 4,922,393, 4,939,420, and D-302,472. In CFL downlight 80, there is a base 82, which includes a conventional threaded connector 98 for engaging an incandescent lamp socket. Housed within the base assembly 82 there is typically an electronic or magnetic ballast. Other options that can be attached to or housed within the base 82 include various heat sink alternatives to cool both the ballast and lamp 86. The lamp unit 86 includes the light emitted tube portion 88, and a connector 84 for electrically connecting the contacts of the lamp with the ballast. In the CFL downlight 80, a replaceable lamp 86 is depicted to enable the lamp to be replaced at failure without having to replace the base assembly 82. Other types of lighting devices, such as that described in U.S. Patent 5,506,474, utilize a design where the lamp, ballast, and base must be replaced as a complete unit. Also shown in Figure 17, the inventive reflective material 92 is mounted inside a reflective cavity 90, the reflective cavity having a cavity aperture 94 and a cavity depth 96. In this particular example, an inventive compact fluorescent downlight was fabricated using a 15 watt screw in compact fluorescent lamp, model number SLS 15W, available from Philips Lighting Company, Somerset, NJ. A cylindrical sheet metal cavity 90 was constructed to substantially surround the light tubes 88 of the lamp. Inventive reflective material 92 made in accordance with Example 5A was then mounted in the reflective cavity to cover both the inside surface of the cylinder and the base of the cavity. The reflective cavity had the following measurements: CA m , n (minimum dimension of cavity aperture) = 87 mm CD max (maximum dimension of cavity depth) = 62 mm R AD (aperture to depth ratio) = 1.4 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 6. EXAMPLE 12 Another inventive compact fluorescent downlight was fabricated using the same 15 watt screw in compact fluorescent lamp as was used in Example 11. Inventive reflective material made in accordance with Example 5A was then mounted in a cylindrical reflective cavity to cover both the inside surface of the cylinder and the base of the cavity. The reflective cavity had the following measurements: CA m , n (minimum dimension of cavity aperture) =148 mm CD max (maximum dimension of cavity depth) = 74 mm R A0 (aperture to depth ratio) = 2.0 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 6. COMPARATIVE EXAMPLE 13 A comparative compact fluorescent downlight model number SLS/R30 15 watt available from Philips Lighting Co was obtained This unit is supplied with its own detachable reflective cavity This luminaire was then tested according to the test method described in Example 10 and reported in Table 6 along with its reflective cavity measurements The lamp which was supplied with this unit was identical to the lamp used in inventive Examples 11 and 12 with the only difference being the reflective cavities As shown in Table 6, the tested efficacy (lumens /watt) of the Example 13 (control) was 44 3 and the efficacy of Examples 11 and 12 was 83 1 and 89 1 , respectively Thus, by replacing the manufacturer supplied reflective cavity of Example 13 with the two inventive reflective cavities of Examples 11 and 12 there was an efficacy increase of 87 6% and 101 1%, respectively COMPARATIVE EXAMPLE 14 A comparative compact fluorescent downlight model number OCR 30WF available from ProLight, Holland, Ml, was obtained This unit was supplied with its own detachable reflective cavity This luminaire was then tested according to the test method described in Example 10 and reported in Table 6 along with its reflective cavity measurements COMPARATIVE EXAMPLE 15 Another comparative compact fluorescent downlight model number X- 18NCRS13Q available from Scientific Component Systems, Tustin, CA, was obtained This unit was supplied with its own reflective cavity This luminaire was then tested according to the test method described in Example 10 and reported in Table 6 along with its reflective cavity measurements COMPARATIVE EXAMPLE 16 Another comparative compact fluorescent downlight model number Soft White Energy Choice Electronic Compact Fluorescent Reflector R-30 available from General Electric, Cleveland, OH, was obtained This unit was supplied with its own reflective cavity This luminaire was then tested according to the test method described in Example 10 and reported in Table 6 along with its reflective cavity measurements As shown in table 6, additional comparative Examples 14 through 16 also had a relatively low tested luminance and efficacy as compared to inventive Examples 11 and 12 TABLE 6 The above examples confirm that although current 15 watt compact fluorescent downlights have improved efficacy over the incandescent lamps for which they are intended to replace, such as the 65 watt GE Miser (comparative Example 10), they fall short of matching the total lumen output Thus the user must sacrifice luminance to save energy This problem is recognized as a deficiency with all of the current CFL downlight designs The above examples thus demonstrate that a 15 watt CFL downlight incorporating a reflector of the present invention offers an increase in efficacy over not only other CFL downlight alternatives, but they even offer more luminance than the incumbent 65 watt incandescent floodlight EXAMPLE 17 Figure 18 represents an inventive recessed compact fluorescent downlight 100 for use in a range of new construction or retrofit applications In recessed CFL downlight 100, there is a compact fluorescent lamp 102 recessed vertically within the reflective cavity 104 having a cavity aperture 118 and a cavity depth 120 The reflective cavity is lined with inventive reflective material 106 such that the lamp is substantially surrounded by the reflective material Power is supplied to the lamp through the socket housing 108 Also shown is the ballast module 110 and junction box 112 The recessed downlight 100 is shown in application mounted in a ceiling 116 and held in place by the ceiling mounting frame 114 As in the above applications either a magnetic or electronic ballast may be used In this particular example, an inventive compact fluorescent downlight was fabricated using a vertical 8020 series downlight frame and ballast assembly number 6113 available from Lightoher, Secaucus, NJ A cylindrical sheet metal cavity 104 was constructed to substantially surround a 13 watt Philips lamp 102 Inventive reflective material 106 made in accordance with Example 5A was then mounted in the reflective cavity to cover both the inside surface of the cylinder and the base of the cavity The reflective cavity had the following measurements CA mιn (minimum dimension of cavity aperture) = 95 mm CD max (maximum dimension of cavity depth) = 83 mm R AD (aperture to depth ratio) = 1 1 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 7 The power (watts) input recorded in the table reflects the power required to drive the lamp along with the ballast included EXAMPLE 18 Another inventive recessed compact fluorescent downlight was fabricated using the same frame and ballast assembly and the same 13 watt compact fluorescent lamp of Example 17 Inventive reflective material made in accordance with Example 5A was then mounted in a cylindrical reflective cavity to cover both the inside surface of the cylinder and the base of the cavity The reflective cavity had the following measurements CA mιn (minimum dimension of cavity aperture) =148 mm CD ma , (maximum dimension of cavity depth) = 156 mm R AD (aperture to depth ratio) = 1 0 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 7 COMPARATIVE EXAMPLE 19 A comparative example (control) was then tested using the factory supplied 8020 reflector, a Philips 13 watt lamp, along with a 8020 series downlight frame and ballast assembly number 6113 available from Lightolier used in Examples 17 and 18 The reflective cavity had the following measurements CA mιn (minimum dimension of cavity aperture) =152 mm CD max (maximum dimension of cavity depth) = 171 mm R AD (aperture to depth ratio) = 0 9 This luminaire was then tested according to the test method described in Example 10 and reported in Table 7 As can be calculated from Table 7, Example 17 had a luminance and an efficacy increase of 30 1% over the control CFL luminaire of Example 19 Example 18 had a luminance and an efficacy increase of 49 6% over the control CFL luminaire of Example 19 EXAMPLE 20 Another inventive recessed compact fluorescent downlight was fabricated using a Vertical 8060 series downlight frame and ballast assembly number 7126 available from Lightolier, Secaucus, NJ A cylindrical sheet metal cavity was constructed to substantially surround a 26 watt Philips lamp Inventive reflective material made in accordance with Example 5A was then mounted in the reflective cavity to cover both the inside surface of the cylinder and the base of the cavity The reflective cavity had the following measurements CA mn (minimum dimension of cavity aperture) = 148 mm CD max (maximum dimension of cavity depth) = 191 mm R AD (aperture to depth ratio) = 0 8 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 8 EXAMPLE 21 Another inventive recessed compact fluorescent downlight was fabricated using the same frame and ballast assembly and the same 26 watt compact fluorescent lamp of Example 20 Inventive reflective material made in accordance with Example 5A was then mounted in a cylindrical reflective cavity to cover both the inside surface of the cylinder and the base of the cavity The reflective cavity had the following measurements CA mιn (minimum dimension of cavity aperture) = 148 mm CD max (maximum dimension of cavity depth) = 165 mm R AD (aperture to depth ratio) = 0 9 The inventive luminaire was then tested according to the test method descπbed in Example 10 and reported in Table 8 COMPARATIVE EXAMPLE 22 A comparative example (control) was then tested using the factory supplied 8060 reflector, a Philips 26 watt lamp, along with the 8060 series downlight frame and ballast assembly number 7126 available from Lightolier used in Examples 20 and 21. The reflective cavity had the following measurements: CA, ™ (minimum dimension of cavity aperture) = 219 mm CD max (maximum dimension of cavity depth) = 254 mm R AD (aperture to depth ratio) = 0.9 mm This luminaire was then tested according to the test method described in Example 10 and reported in Table 8. COMPARATIVE EXAMPLE 23 Another comparative example, a 2 x 26 watt horizontal lamp 8056 series was tested. This luminaire used a factory supplied 8056 reflector, two Philips 26 watt compact fluorescent lamps, along with a 8056 series downlight frame and ballast assembly number 7226 available from Lightolier. The reflective cavity had the following measurements: CA mιn (minimum dimension of cavity aperture) = 186 mm CD max (maximum dimension of cavity depth) = 171 mm R AD (aperture to depth ratio) = 1.1 This luminaire was then tested according to the test method described in Example 10 and reported in Table 8. TABLE 8 As can be calculated from Table 8, Examples 20 and 21 had both a luminance and efficacy increase of 46 4% and 60 5%, respectively, over Example 22 (control) Furthermore, inventive Example 21 had 3.6% more luminance than comparative Example 23 even though only one lamp versus two lamps were used thereby using only half the input power EXAMPLE 24 Another inventive compact fluorescent downlight was fabricated using the same model number X-18NCRS13Q available from Scientific Component Systems, Tustin, CA, as was used in Example 15 The reflective cavity was modified by lining it with 1 5 mm ePTFE made in accordance with Example 5A This luminaire was then tested according to the test method described in Example 10 and reported in Table 9 COMPARATIVE EXAMPLE 25 The comparative compact fluorescent downlight from Example 15 was modified by removing the plastic diffuser lens This luminaire was then tested according to the test method described in Example 10 and reported in Table 9 EXAMPLE 26 Another inventive compact fluorescent downlight was fabricated using the luminaire from Example 25 (no lens) The reflective cavity was modified by lining it with 1 5 mm ePTFE made in accordance with Example 5A This luminaire was then tested according to the test method described in Example 10 and reported in Table 9 As can be seen in Table 9, in Examples 15 and 24 (with lens) by increasing the reflectance of the cavity from 88 0% to 99 1 % there is a luminance increase of 45 0% This creates a luminance increase to reflectance increase ratio of 4 1 Furthermore, in the Examples 25 and 26 (without lens) there was a similar luminance increase of 42 3% with a luminance increase to reflectance increase ratio of 3 8 One can see that with both of the comparative and inventive examples, the lens significantly decreases the luminance However, it is important to note that not only did the inventive Example 24 (with lens) have a higher luminance than its sibling Comparative Example 15 (with lens), it also had a higher luminance than the Comparative Example 25 (without lens) EXAMPLE 27 The 1 5 mm thick reflective material from the inventive compact fluorescent downlight of Example 11 was replaced with a 1 0 mm thick reflective material made in accordance with Sample 2 of Example 4 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 10 EXAMPLE 28 The 1 5 mm thick reflective material from the inventive compact fluorescent downlight of Example 11 was replaced with a 0 5 mm thick reflective material made in accordance with Sample 1 of Example 4 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 10 EXAMPLE 29 The 1 5 mm thick reflective material from the inventive compact fluorescent downlight of Example 11 was replaced with a 0 22 mm thick reflective material made in accordance with Example 5 The inventive luminaire was then tested according to the test method described in Example 10 and reported in Table 10 Table 10 depicts the performance of an inventive luminaire which has been modified with four inventive reflective materials having different levels of reflectance For ease of comparison, reflectance levels at 550 nanometer wavelength have been listed for each material The incremental reflectance increase column refers to the additional reflectance measured at 550 nanometers based on increased thickness The incremental luminance increase column refers to the measured increased luminance output in percent due to the additional reflectance of the thicker materials As can be seen in Table 10, by increasing the inventive reflective material thickness from 0 22 to 0 5 mm, the reflectance of the material increases by 3 3% Mounted in the reflective cavity of the luminaire, this reflectance increase yields a luminance increase of 10 4% This creates an incremental luminance increase to incremental reflectance increase ratio of 3 2 By increasing the inventive reflective mateπal thickness from 0 5 to 1 0 mm, the reflectance of the material increases by 0 9% Mounted in the reflective cavity of the luminaire, this reflectance increase yields a luminance increase of 4 8% This creates an incremental luminance increase to incremental reflectance increase ratio of 5 3 By increasing the inventive reflective material thickness from 1 0 to 1 5 mm, the reflectance of the material increases by 0 5% Mounted in the reflective cavity of the luminaire, this reflectance increase yields a luminance increase of 5 3% This creates an incremental luminance increase to incremental reflectance increase ratio of 10 6 It has been demonstrated in this example, as diffuse reflectance of the cavity approaches 100%, smaller incremental increases in percent reflectance bring about larger incremental gains in luminance Thus, it has been demonstrated that in applications where a compact fluorescent lamp is substantially surrounded by a highly diffuse reflective cavity stepping up from 94% to 95% to 96% to 97% to 98% to 99% reflectance, extraordinary escalating luminance and efficacy gams can be realized that have never before been previously achieved As has been noted, the dramatic improvements achieved through the use of the inventive material of the present invention occur due to the compounded effect of fluorescent light generated in a CFL fixture When the depth of the fixture approaches the size of the opening through which light is emitted, any lack of complete reflectance of the reflector is significantly compounded Where the depth of the fixture is greater than the size of the aperture, incomplete reflectance will result in measurable light loss In light of the compound effect, the present invention is believed to be particularly beneficial in those instances where the ratio of the lamp fixture aperture to the depth of the lamp fixture is less than about 2 0 As this ratio decreases, the reflectance gam of the present invention tends to become even more crucial Thus, the present invention is very useful where the ratio is less than about 1 5 and even more so where the ratio is less than about 1 0 The above examples make it clear that by increasing the thickness of an expanded PTFE sheet used as a reflector, a marked increase in reflectance can be achieved Naturally, a lamp manufacturer must balance gains in light output against space constraints of a CFL in choosing the type and thickness of expanded PTFE used in the present invention For most applications using an expanded PTFE sheet such as that described in Examples 4 and 5, a thickness of 0 5 to 2 2 mm should be suitable for most CFL applications For many applications an ePTFE sheet with a thickness less than 3 mm would be particularly useful Where feasible, it is believed that significant improvements in reflectance can be achieved by using such expanded PTFE sheets up to a thickness of about 0 5 to 6 2 mm However, as has been noted, the present invention provides important improvements in reflectance even as relatively thin embodiments of 0 22 to 0 5 mm or less While it is preferable to use expanded PTFE as the reflectant material for the reflective cavity of the present invention due to its many desired attributes, other highly diffuse reflectant materials having reflectance levels equal to or greater than 94% may also be used in achieve some of the improvements of the present invention For instance, materials that may also provide benefits in CFL applications include SPECTRALON PTFE, barium sulfate, magnesium oxide, aluminum oxide, titanium dioxide, PTFE, and other powders or paints It is contemplated within the scope of this invention to include all of the above mentioned reflective materials to be used in the reflective cavity which substantially surrounds the compact fluorescent lamp in a luminaire Figure 19 represents another inventive recessed compact fluorescent downlight 130 for use in a range of new construction or retrofit applications In recessed CFL downlight 130, there are two compact fluorescent lamps 132 recessed horizontally within the reflective cavity 134 having an cavity aperture 136 and a cavity depth 138 The reflective cavity is lined with inventive reflective material 140 such that the lamps are substantially surrounded by the reflective material Power is supplied to the lamps through the socket housing 142 Also shown are the ballast modules 144 and junction box 146 The recessed downlight 130 is shown in application mounted in a ceiling 148 and held in place by the ceiling mounting frame 150 As in the above applications either magnetic or electronic ballasts may be used In this particular example, the reflective cavity 134 has an upper chamber 152 and lower chamber 154 Also, there is a specular reflector 156, incorporated at the base of the upper chamber 152 This inventive example is intended to demonstrate that it is within the scope of this invention to include hybrid reflective cavities that utilize the inventive reflective material along with other reflective materials This example also demonstrates that it is within the scope of this invention to have lamps positioned other than vertical, which may include horizontal and even angled positions such as those described in U S Patent 4,922,393 Figure 20 represents another inventive compact fluorescent downlight application where the lamp is substantially surrounded in a recessed cavity Typically this configuration is used for track lighting, task lighting, and other directional lighting In CFL track light 160, there is a compact fluorescent lamp 162 recessed within the reflective cavity 164 having a cavity aperture 166 and a cavity depth 168 The reflective cavity is lined with inventive reflective material 170 such that the lamp is substantially surrounded by the reflective material The recessed downlight 160 is shown in application mounted from a ceiling bracket 172 While particular embodiments of the present invention have been illustrated and descπbed herein, the present invention should not be limited to such illustrations and descriptions It should be apparent that changes and modifications may be incorporated and embodied as part of the present invention within the scope of the following claims

Claims: The invention claimed is: 1. A method of providing improved diffuse reflectivity of light in a luminaire containing a compact fluorescent lamp comprising; providing a reflectant material comprising an expanded polytetrafluoroethylene having polymeric nodes interconnected by fibrils defining microporous voids therein; with the reflectant material having a diffuse reflectance of greater than 94% mounting the reflectant material in a recessed cavity of a luminaire to substantially surround the lamp so as to cause light energy to reflect off it, the recessed cavity having an aperture to depth ratio of equal to or less than 2.0. 2. The method of claim 1 that further comprises providing a reflectant material that has a diffuse reflectance of greater than 95%. 3. The method of claim 1 that further comprises providing a reflectant material that has a diffuse reflectance of greater than 96%. 4. The method of claim 1 that further comprises providing a reflectant material that has a diffuse reflectance of greater than 97%. 5. The method of claim 1 that further comprises providing a reflectant material that has a diffuse reflectance of greater than 98%. 6. The method of claim 1 that further comprises providing a reflectant material that has a diffuse reflectance of greater than 99%. 7. The method of claim 1 that further comprises providing a recessed cavity having an aperture to depth ratio of less than 1.5. 8. The method of claim 1 that further comprises providing a recessed cavity having an aperture to depth ratio of less than 1.0. 9. The method of claim 1 that further comprises providing an expanded polytetrafluoroethylene sheet that is flexible and is molded to fit within the luminaire. 10. The method of claim 1 that further comprises providing a reflectant material having a thickness of less than about 3 mm. 11. A luminaire comprising at least one compact fluorescent lamp mounted in the luminaire; at least one sheet of expanded polytetrafluoroethylene (PTFE) comprising a structure of nodes and fibrils having a reflectance of greater than 94%; mounting the reflectant material in a recessed cavity of the luminaire to substantially surround the lamp so as to cause light energy to reflect off it, the recessed cavity having an aperture to depth ratio of equal to or less than 2.0 12 The luminaire of claim 1 1 wherein the recessed cavity has an aperture to depth ratio of less than 1 5 13 The luminaire of claim 11 wherein the recessed cavity has an aperture to depth ratio of less than 1 0 14 The luminaire of claim 11 wherein the reflectant material has a reflectance greater than 95% 15 The luminaire of claim 11 wherein the reflectant material has a reflectance greater than 96% 16 The luminaire of claim 1 1 wherein the reflectant material has a reflectance greater than 97% 17 The luminaire of claim 11 wherein the reflectant material has a reflectance greater than 98% 18 The luminaire of claim 11 wherein the reflectant material has a reflectance greater than 99% 19 The luminaire of claim 11 wherein the expanded polytetrafluoroethylene is flexible and is molded to fit within the luminaire 20 The luminaire of claim 11 wherein the reflectant material has a thickness of less than about 3 mm 21 A luminaire compπsing at least one compact fluorescent lamp mounted in the luminaire, a reflectant cavity lined with polytetrafluoroethylene (PTFE) having a reflectance of greater than 94%, the reflectant cavity of the luminaire to substantially surround the lamp so as to cause light energy to reflect off it, the reflectant cavity having an aperture to depth ratio of equal to or less than 2.0 22 The luminaire of claim 21 where the reflectant cavity has a reflectance greater than 96% 23 The luminaire of claim 25 where the reflectant cavity has a reflectance greater than 98% 24 A luminaire compπsing at least one compact fluorescent lamp mounted in the luminaire, a reflectant cavity having a reflectance of greater than 94%; the reflectant cavity of the luminaire to substantially surround the lamp so as to cause light energy to reflect off it, the reflectant cavity having an aperture to depth ratio of equal to or less than 2.0. 25. The luminaire of claim 24 wherein the reflectant cavity has a reflectance greater than 96%. 26. The luminaire of claim 24 wherein the reflectant cavity has a reflectance greater than 98%.

Inventors: HANNON GREGORY E, MCGREGOR GORDON L, MINOR RAYMOND B, HANNON, GREGORY, E., MCGREGOR, GORDON, L., MINOR, RAYMOND, B.
Applicants: GORE & ASS, W.L. GORE & ASSOCIATES, INC.
Application year: 1997
Main classification: F21V7
IPC codes: F21V7, G02B5