1. Field of the Invention
The invention relates generally to reflector systems for lighting applications and, more particularly, to reflector systems for multi-element light sources.
2. Description of the Related Art
Light emitting diodes (LED or LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is emitted from the active region and from surfaces of the LED.
In order to generate a desired output color, it is sometimes necessary to mix colors of light which are more easily produced using common semiconductor systems. Of particular interest is the generation of white light for use in everyday lighting applications. Conventional LEDs cannot generate white light from their active layers; it must be produced from a combination of other colors. For example, blue emitting LEDs have been used to generate white light by surrounding the blue LED with a yellow phosphor, polymer or dye, with a typical phosphor being cerium-doped yttrium aluminum garnet (Ce:YAG). The surrounding phosphor material “downconverts” some of the LED's blue light, changing its color to yellow. Some of the blue light passes through the phosphor without being changed while a substantial portion of the light is downconverted to yellow. The LED emits both blue and yellow light, which combine to provide a white light.
In another known approach light from a violet or ultraviolet emitting LED has been converted to white light by surrounding the LED with multicolor phosphors or dyes. Indeed, many other color combinations have been used to generate white light.
Because of the physical arrangement of the various source elements, multicolor sources often cast shadows with color separation and provide an output with poor color uniformity. For example, a source featuring blue and yellow sources may appear to have a blue tint when viewed head on and yellow tint when viewed from the side. Thus, one challenge associated with multicolor light sources is good spatial color mixing over the entire range of viewing angles.
One known approach to the problem of color mixing is to use a diffuser to scatter light from the various sources; however, a diffuser usually results in a wide beam angle. Diffusers may not be feasible where a narrow, more controllable directed beam is desired.
Another known method to improve color mixing is to reflect or bounce the light off of several surfaces before it is emitted. This has the effect of disassociating the emitted light from its initial emission angle. Uniformity typically improves with an increasing number of bounces, but each bounce has an associated loss. Many applications use intermediate diffusion mechanisms (e.g., formed diffusers and textured lenses) to mix the various colors of light. These devices are lossy and, thus, improve the color uniformity at the expense of the optical efficiency of the device.
Many modern lighting applications demand high power LEDs for increased brightness. High power LEDs can draw large currents, generating significant amounts of heat that must be managed. Many systems utilize heat sinks which must be in good thermal contact with the heat-generating light sources. Some applications rely on cooling techniques such as heat pipes which can be complicated and expensive.
One exemplary embodiment of a light emitting device according to the present invention comprises the following elements. A multi-element light source is mounted at the base of a secondary reflector. The secondary reflector is adapted to shape and direct an output light beam. A primary reflector is disposed proximate to the light source to redirect light from the source toward the secondary reflector. The primary reflector is shaped to reflect light from the multi-element source such that the light is spatially mixed prior to incidence on the secondary reflector.
One exemplary embodiment of a lamp device according to the present invention comprises the following elements. A protective housing surrounds a multi-element light source. The housing has an open end through which light may be emitted. A secondary reflector is disposed inside the housing and around the light source such that the light source is positioned at the center of the base of the secondary reflector. A primary reflector is disposed to reflect light emitted from the source toward the secondary reflector such that the light is spatially mixed prior to incidence on the secondary reflector. A lens plate is disposed over the open end of the housing.
a is a cross-sectional view of a lamp device along its diameter according to one embodiment of the present invention.
b is a perspective view with an exposed cross-section of a lamp device according to one embodiment of the present invention.
a is a perspective view of a secondary reflector according to an embodiment of the present invention.
b is a perspective view of a secondary reflector according to an embodiment of the present invention.
Embodiments of the present invention provide a reflector system for lighting applications, especially multi-source solid state systems. The system works particularly well with multicolor light emitting diode (LED) arrangements to provide a tightly focused beam of white light with good spatial color uniformity. The sources can be chosen to produce varying shades of white light (e.g., warmer whites or cooler whites) or colors of light other than white. Applications range from commercial and industrial lighting to military, law enforcement and other specialized uses.
The system uses two reflective surfaces to redirect the light before it is emitted. This is sometimes referred to as a “double-bounce” configuration. The light source/sources are disposed at the base of the secondary reflector. The first reflective surface is provided by the primary reflector which is arranged proximate to the source/sources. The primary reflector initially redirects, and in some cases diffuses, light from the sources such that the different wavelengths of light are mixed as they are redirected toward the secondary reflector. The secondary reflector functions primarily to shape the light into a desired output beam. Thus, the primary reflector is used color mix the light, and the secondary reflector is used to shape the output beam. The reflector arrangement allows the source to be placed at the base of the secondary reflector where it may be thermally coupled to a housing or another structure to provide an outlet for heat generated by the sources.
It is understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. Furthermore, relative terms such as “inner”, “outer”, “upper”, “above”, “lower”, “beneath”, and “below”, and similar terms, may be used herein to describe a relationship of one element to another. It is understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.
Although the ordinal terms first, second, etc., may be used herein to describe various elements, components, regions and/or sections, these elements, components, regions, and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, or section from another. Thus, unless expressly stated otherwise, a first element, component, region, or section discussed below could be termed a second element, component, region, or section without departing from the teachings of the present invention.
As used herein, the term “source” can be used to indicate a single light emitter or more than one light emitter functioning as a single source. For example, the term may be used to describe a single blue LED, or it may be used to describe a red LED and a green LED in proximity emitting as a single source. Thus, the term “source” should not be construed as a limitation indicating either a single-element or a multi-element configuration unless clearly stated otherwise.
The term “color” as used herein with reference to light is meant to describe light having a characteristic average wavelength; it is not meant to limit the light to a single wavelength. Thus, light of a particular color (e.g., green, red, blue, yellow, etc.) includes a range of wavelengths that are grouped around a particular average wavelength.
A primary reflector 104 is disposed proximate to the light source 102. The light emitted from the source 102 interacts with the primary reflector 104 such that the color is mixed as it is redirected toward a secondary reflector 106. The secondary reflector 106 receives the mixed light and shapes it into a beam having characteristics that are desirable for a given application. A protective housing 108 surrounds the light source 102 and the reflectors 104, 106. The source 102 is in good thermal contact with the housing 108 at the base of the secondary reflector 106 to provide a pathway for heat to escape into the ambient. A lens plate 110 covers the open end of the housing 108 and provides protection from outside elements. Protruding inward from the lens plate 110 is a mount post 112 that holds the primary reflector 104 in place, proximate to the light source 102.
The light source 102 may comprise one or more emitters producing the same color of light or different colors of light. In one embodiment, a multicolor source is used to produce white light. Several colored light combinations will yield white light. For example, it is known in the art to combine light from a blue LED with wavelength-converted yellow light to create a white output. Both blue and yellow light can be generated with a blue emitter by surrounding the emitter with phosphors that are optically responsive to the blue light. When excited, the phosphors emit yellow light which then combines with the blue light to make white. In this scheme, because the blue light is emitted in a narrow spectral range it is called saturated light. The yellow light is emitted in a much broader spectral range and, thus, is called unsaturated light. Another example of generating white light with a multicolor source is combining the light from green and red LEDs. RGB schemes may be used to generate various colors of light. Sometimes an amber emitter is added for a RGBA combination. The previous combinations are exemplary; it is understood that many different color combinations may be used in embodiments of the previous invention. Several of these possible color combinations are discussed in detail in U.S. Pat. No. 7,213,940 to Van de Ven et al. which is commonly assigned with the present application to CREE LED LIGHTING SOLUTIONS, INC. and fully incorporated by reference herein.
Color combination can be achieved with a singular device having multiple chips or with multiple discreet devices arranged in proximity to each other. For example, the source 102 may comprise a multicolor monolithic structure (chip-on-board) bonded to a printed circuit board (PCB). In some embodiments, several LEDs are mounted to a submount to create a single compact optical source. Examples of such structures can be found in U.S. patent application Ser. Nos. 12/154,691 and 12/156,995, both of which are commonly assigned to CREE, INC., and both of which are fully incorporated by reference herein. In the embodiment shown in
The encapsulant 114 may also contain light scattering particles to help with the color mixing process in the near field. Although light scattering particles dispersed within the encapsulant 114 may cause optical losses, it may be desirable in some applications to use them in concert with the reflectors 104, 106 so long as the optical efficiency is acceptable.
Color mixing in the near field may be aided by providing a scattering/diffuser material or structure in close proximity to the light sources. The diffuser is in, on, or remote from, but in close proximity to, the LED chips with the diffuser arranged so that the lighting/LED component can have a low profile while still mixing the light from the LED chips in the near field. By diffusing in the near field, the light may be pre-mixed to a degree prior to interacting with either reflector.
A diffuser can comprise many different materials arranged in many different ways. In some embodiments, a diffuser film can be provided on the encapsulant 114. In other embodiments, the diffuser can be included within the encapsulant 114. In still other embodiments, the diffuser can be remote from the encapsulant, but not so remote as to provide substantial mixing from the reflection of light external to the lens. Many different structures and materials can be used as a diffuser such as scattering particles, geometric scattering structures or microstructures, diffuser films comprising microstructures, or diffuser films comprising index photonic films. The diffuser can take many different shapes over the LED chips; it can be flat, hemispheric, conic, and variations of those shapes, for example.
The encapsulant 114 may also function as a lens to shape the beam prior to incidence on the primary reflector 104.
Light emitted from the source is first incident on the primary reflector 104. The primary reflector 104 is disposed proximate to the source 102 so that substantially all of the emitted light interacts with it. In one embodiment the mount post 112 supports the primary reflector 104 in position near the source 102. A screw, an adhesive, or any other means of attachment may be used to secure the primary reflector 104 to the mount post 112. Because the mounting post 112 is hidden behind the primary reflector 104 relative to the source 102, the mounting post 112 blocks very little light as it exits through the lens plate 110.
The primary reflector 104 may comprise a specular reflective material or a diffuse material. If a specular material is used, the primary reflector 104 may be faceted to prevent the source from imaging in the output. One acceptable material for a specular reflector is a polymeric material that has been vacuum metallized with a metal such as aluminum or silver. Another acceptable material would be optical grade aluminum that is shaped using a known process, such as stamping or spinning. The primary reflector 104 may be shaped from a material that is itself reflective, or it may be shaped and then covered or coated with a thin film of reflective material. If a specular material is used, the primary reflector 104 will preferably have a reflectivity of no less than 88% in the relevant wavelength ranges.
The primary reflector 104 may also comprise a highly reflective diffuse white material, such as a microcellular polyethylene terephthalate (MCPET). In such an embodiment, the primary reflector 104 functions as a reflector and a diffuser.
The primary reflector 104 can be shaped in many different ways to reflect the light from the source 102 toward the secondary reflector 106. In the embodiment shown in
The primary reflector 104 mixes the light and redirects it toward the secondary reflector 106. The secondary reflector 106 may be specular or diffuse. Many acceptable materials may be used to construct the secondary reflector 106. For example, a polymeric material which has been flashed with a metal may used. The secondary reflector 106 can also be made from a metal, such as aluminum or silver.
The secondary reflector 106 principally functions as a beam shaping device. Thus, the desired beam shape will influence the shape of the secondary reflector 106. The secondary reflector 106 is disposed such that it may be easily removed and replaced with other secondary reflectors to produce an output beam having particular characteristics. In the embodiment shown in
The secondary reflector 106 may be held inside the housing 108 using known mounting techniques, such as screws, flanges, or adhesives. In the embodiment of
The protective housing 108 surrounds the reflectors 104, 106 and the source 102 to shield these internal components from the elements. The lens plate 110 and the housing 108 may form a watertight seal to keep moisture from entering into the internal areas of the device 100. A portion of the housing 108 may comprise a material that is a good thermal conductor, such as aluminum or copper. The thermally conductive portion of the housing 108 can function as a heat sink by providing a path for heat from the source 102 through the housing 108 into the ambient. The source 102 is disposed at the base of the secondary reflector 106 such that the housing 108 can form good thermal contact with the source 102. Thus, the source 102 may comprise high power LEDs that generate large amounts of heat.
Power is delivered to the source 102 through a protective conduit 116. The lamp device 100 may be powered by a remote source connected with wires running through the conduit 116, or it may be powered internally with a battery that is housed within the conduit 116. The conduit 116 may be threaded as shown in
The physical arrangement of the emitters 302, 304, 306 on the surface 310 will cause some non-uniform color distribution (i.e., imaging) in the output if the colors are not mixed prior to escaping the lamp device 100. The double bounce from the primary reflector 102 to the secondary reflector 106 mixes the colors and prevents imaging of the LED arrangement in the output. The color of the output light is controlled by the emission levels of the individual emitters 302, 304, 306. A controller circuit may be employed to select the emission color by regulating the current to each of the emitters 302, 304, 306.
a and 9b show two views of a lamp device 900.
The tube element 902 may be cylindrical as shown in
In this embodiment, the primary reflector has a notch 908 around the perimeter of the substantially conic structure. The tube element 902 cooperates with the notch 908 such that the inside surface of the tube element 902 abuts the circumferential outer surface of the notch 908. The tube element 902 may have an inner diameter such that it fits snugly over the notch 908, aligning and stabilizing the adjoined elements. The notch 908 functions not only as an alignment mechanism, it also reduces the amount of light that bleeds out between tube element 908 and the primary reflector 904 by effectively shielding the joint from the emitted light.
a and 12b show two perspective views of an embodiment of a secondary reflector 1200. Unlike the smooth bowl-shape of the secondary reflector 106 shown in
Although the present invention has been described in detail with reference to certain preferred configurations thereof, other versions are possible. For example, embodiments of the lamp device may include various combinations of primary and secondary reflectors discussed herein. Therefore, the spirit and scope of the invention should not be limited to the versions described above.