Patent Application
20210018153
The invention relates to troffer-style lighting fixtures and, more particularly, to troffer-style fixtures that are well-suited for use with solid state lighting sources, such as light emitting diodes (LEDs).
Troffer-style fixtures are ubiquitous in commercial office and industrial spaces throughout the world. In many instances these troffers house elongated fluorescent light bulbs that span the length of the troffer. Troffers may be mounted to or suspended from ceilings. Often the troffer may be recessed into the ceiling, with the back side of the troffer protruding into the plenum area above the ceiling. Typically, elements of the troffer on the back side dissipate heat generated by the light source into the plenum where air can be circulated to facilitate the cooling mechanism. U.S. Pat. No. 5,823,663 to Bell, et al. and U.S. Pat. No. 6,210,025 to Schmidt, et al. are examples of typical troffer-style fixtures.
More recently, with the advent of the efficient solid state lighting sources, these troffers have been used with LEDs, for example. 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 produced in the active region and emitted from surfaces of the LED.
LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent or fluorescent lights. Incandescent lights are very energy-inefficient light sources with approximately ninety percent of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs by a factor of about 10, but are still relatively inefficient. LEDs by contrast, can emit the same luminous flux as incandescent and fluorescent lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours. The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in their LED lights being used in place of conventional lighting in many different applications. It is predicted that further improvements will result in their general acceptance in more and more lighting applications. An increase in the adoption of LEDs in place of incandescent or fluorescent lighting would result in increased lighting efficiency and significant energy saving.
Other LED components or lamps have been developed that comprise an array of multiple LED packages mounted to a (PCB), substrate or submount. The array of LED packages can comprise groups of LED packages emitting different colors, and specular reflector systems to reflect light emitted by the LED chips. Some of these LED components are arranged to produce a white light combination of the light emitted by the different LED chips.
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 blue light, changing it to yellow light. 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 yield 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.
Some recent designs have incorporated an indirect lighting scheme in which the LEDs or other sources are aimed in a direction other than the intended emission direction. This may be done to encourage the light to interact with internal elements, such as diffusers, for example. One example of an indirect fixture can be found in U.S. Pat. No. 7,722,220 to Van de Ven which is commonly assigned with the present application.
Modern lighting applications often 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. Troffer-style fixtures generally dissipate heat from the back side of the fixture that extends into the plenum. This can present challenges as plenum space decreases in modern structures. Furthermore, the temperature in the plenum area is often several degrees warmer than the room environment below the ceiling, making it more difficult for the heat to escape into the plenum ambient.
An embodiment of a lighting assembly comprises the following elements. An elongated heat sink is shaped to define a conduit running longitudinally through the interior of the heat sink. A reflector is proximate to the heat sink, the reflector comprising a surface facing the heat sink and a back surface. The heat sink and reflector are mountable to a first end cap.
An embodiment of a modular lighting assembly comprises the following elements. At least one lighting unit is capable of being connected to additional lighting units in an end-to-end serial arrangement. Each lighting unit comprises an elongated heat sink, a reflector proximate to the heat sink, a first end cap, and a second end cap. The heat sink and the reflector are mounted between the first end cap and the second end cap.
An embodiment of a lighting assembly comprises the following elements. An elongated heat sink comprises a mount surface. The heat sink is shaped to define a conduit running longitudinally through the interior of the heat sink. Light emitters are on said mount surface. An electrical conductor running through the heat sink conduit can provide power to said light emitters. A reflector comprises a surface facing toward the light emitters. First and second end caps comprise mount structures such that the heat sink and the reflector mount between the first and second end caps, the first end cap housing electronics for powering said light emitters.
Embodiments of the present invention provide a modular troffer-style fixture that is particularly well-suited for use with solid state light sources, such as LEDs. The fixture comprises a reflector having a surface on one side and a back surface on the opposite side. The back surface includes parallel rails that run along the length of the reflector, providing a mount mechanism as well structural support to the reflector. To facilitate the dissipation of unwanted thermal energy away from the light sources, a heat sink is disposed proximate to the surface of the reflector. The portion of the heat sink facing the reflector functions as a mount surface for the light sources, creating an efficient thermal path from the sources to the ambient. The heat sink, which is exposed to the ambient room environment, is hollow through the center in the longitudinal direction. The hollow portion defines a conduit through which electrical conductors (e.g., wires) can be run to power light emitters. One or more light emitters disposed along the heat sink mount surface emit light toward the reflector where it can be mixed and/or shaped before it is emitted from the troffer as useful light. End caps are arranged at both ends of the reflector and heat sink. One of the end caps houses electronics for powering the light emitters. The end caps are constructed to allow for the easy connection of multiple units in a serial arrangement.
In this embodiment of the lighting assembly 100, the heat sink 104 is exposed to the ambient environment. This structure is advantageous for several reasons. For example, air temperature in a typical residential or commercial room is much cooler than the air above the fixture (or the ceiling if the fixture is mounted above the ceiling plane). The air beneath the fixture is cooler because the room environment must be comfortable for occupants; whereas in the space above the fixture, cooler air temperatures are much less important. Additionally, room air is normally circulated, either by occupants moving through the room or by air conditioning. The movement of air throughout the room helps to break the boundary layer, facilitating thermal dissipation from the heat sink 104. Also, in ceiling-mounted embodiments, a room-side heat sink configuration prevents improper installation of insulation on top of the heat sink as is possible with typical solid state lighting applications in which the heat sink is disposed on the ceiling-side. This guard against improper installation can eliminate a potential fire hazard.
The reflector 102 can be constructed from many different materials. In one embodiment, the reflector 102 comprises a material which allows the reflector 102 to be extruded for efficient, cost-effective production. Some acceptable materials include polycarbonates, such as Makrolon 6265X or FR6901 (commercially available from Bayer) or BFL4000 or BFL2000 (commercially available from Sabic). Many other materials may also be used to construct the reflector 102. Using an extrusion process for fabrication, the reflector 102 is easily scalable to accommodate lighting assemblies of varying length.
The surface 106 may be designed to have several different shapes to perform particular optical functions, such as color mixing and beam shaping, for example. Emitted light may be bounced off of one or more surfaces, including the surface 106. 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 optical loss. In some embodiments an intermediate diffusion mechanism (e.g., formed diffusers and textured lenses) may be used to mix the various colors of light.
The surface 106 should be highly reflective in the wavelength ranges of the light emitters. In some embodiments, the surface 106 may be 93% reflective or higher. In other embodiments it may be at least 95% reflective or at least 97% reflective.
The surface 106 may comprise many different materials. For many indoor lighting applications, it is desirable to present a uniform, soft light source without unpleasant glare, color striping, or hot spots. Thus, the surface 106 may comprise a diffuse white reflector such as a microcellular polyethylene terephthalate (MCPET) material or a Dupont/WhiteOptics material, for example. Other white diffuse reflective materials can also be used.
Diffuse reflective coatings have the inherent capability to mix light from solid state light sources having different spectra (i.e., different colors). These coatings are particularly well-suited for multi-source designs where two different spectra are mixed to produce a desired output color point. For example, LEDs emitting blue light may be used in combination with other sources of light, e.g., yellow light to yield a white light output. A diffuse reflective coating may eliminate the need for additional spatial color-mixing schemes that can introduce lossy elements into the system; although, in some embodiments it may be desirable to use a diffuse surface in combination with other diffusive elements. In some embodiments, the surface may be coated with a phosphor material that converts the wavelength of at least some of the light from the light emitting diodes to achieve a light output of the desired color point.
By using a diffuse white reflective material for the surface 106 and by positioning the light sources to emit light first toward the surface 106 several design goals are achieved. For example, the surface 106 performs a color-mixing function, effectively doubling the mixing distance and greatly increasing the surface area of the source. Additionally, the surface luminance is modified from bright, uncomfortable point sources to a much larger, softer diffuse reflection. A diffuse white material also provides a uniform luminous appearance in the output. Harsh surface luminance gradients (max/min ratios of 10:1 or greater) that would typically require significant effort and heavy diffusers to ameliorate in a traditional direct view optic can be managed with much less aggressive (and lower light loss) diffusers achieving max/min ratios of 5:1, 3:1, or even 2:1.
The surface 106 can comprise materials other than diffuse reflectors. In other embodiments, the surface 106 can comprise a specular reflective material or a material that is partially diffuse reflective and partially specular reflective. In some embodiments, it may be desirable to use a specular material in one area and a diffuse material in another area. For example, a semi-specular material may be used on the center region with a diffuse material used in the side regions to give a more directional reflection to the sides. Many combinations are possible.
The reflector back surface 108 comprises elongated rails 204 that run longitudinally along the reflector 102. The rails 204 perform important dual functions. They provide a mechanism by which the assembly 100 can be mounted to an external surface, such as a ceiling. At the same time, the rails 204 also provide structural support, preventing longitudinal bending along the length of the assembly 100 which allows longer reflector components to be used. The rails 204 may comprise features on the inner and outer surfaces, such as inner flanges 208 and outer flanges 210. The flanges 208, 210 may interface with external elements, such as mounting structures, for example, and may take many different shapes depending on the design of the structures used for mounting. The rails 204 may also comprise many other features necessary for mounting or other purposes.
In this particular embodiment, a U-shaped mount bracket 206 is connected to the inner flange 208. The outer flanges 210 may be used for alternate mounting configurations discussed herein. The mounting bracket 206 removably connects to the rails 204 using snap-fit or slide-fit mechanisms, for example. The mount bracket 206 can be used to mount the light assembly 100 to a surface, such as a ceiling, when the assembly is mounted by suspension. The mounting bracket 206 may be made of metal, plastic, or other materials that are strong enough to support the weight of the assembly 100.
The heat sink 500 can be constructed using many different thermally conductive materials. For example, the heat sink 500 may comprise an aluminum body 504. Similarly as the reflector 102, the heat sink 500 can be extruded for efficient, cost-effective production and convenient scalability.
The heat sink mount surface 506 provides a substantially flat area on which one or more light sources can be mounted. In some embodiments, the light sources will be pre-mounted on light strips.
Many industrial, commercial, and residential applications call for white light sources. The light assembly 100 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 (blue-shifted-yellow or “BSY”) light to yield white light with correlated color temperature (CCT) in the range between 5000K to 7000K (often designated as “cool white”). Both blue and BSY 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 BSY 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 also be used to generate various colors of light. In some applications, an amber emitter is added for an RGBA combination. The previous combinations are exemplary; it is understood that many different color combinations may be used in embodiments of the present 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.
The lighting strips 700, 720, 740 each represent possible LED combinations that result in an output spectrum that can be mixed to generate white light. Each lighting strip can include the electronics and interconnections necessary to power the LEDs. In some embodiments the lighting strip comprises a printed circuit board with the LEDs mounted and interconnected thereon. The lighting strip 700 includes clusters 702 of discrete LEDs, with each LED within the cluster 702 spaced a distance from the next LED, and each cluster 702 spaced a distance from the next cluster 702. If the LEDs within a cluster are spaced at too great distance from one another, the colors of the individual sources may become visible, causing unwanted color-striping. In some embodiments, an acceptable range of distances for separating consecutive LEDs within a cluster is not more than approximately 8 mm.
The scheme shown in
The lighting strip 720 includes clusters 722 of discrete LEDs. The scheme shown in
The lighting strip 740 includes clusters 742 of discrete LEDs. The scheme shown in
The lighting schemes shown in
The modular assembly 900 comprises two individual assemblies 100 as shown. In this particular embodiment, each assembly 100 is approximately 8 ft long. However, because the reflector 102 and heat sink 104 components can be fabricated by extrusion, the assemblies 100 can easily be scaled to a desired length. For example, other modular assemblies could comprise individual units having lengths of 2 ft, 4 ft, 6 ft, etc. Additionally, individual units of different lengths can be combined to construct a modular assembly having a particular size. For example a 2 ft unit can be connected to an 8 ft unit to construct a 10 ft modular assembly. This is advantageous when designing modular assemblies for rooms having particular dimensions. Thus, it is understood that the assemblies can have many different lengths. More than two of the assemblies can be connected to provide a longer series.
The base material 156 provides structural support to the reflector 150 and allows for transmission through areas of the surface 152 where the reflective material 158 is very thin or non-existent. For example, the reflector 150 comprises transmissive windows 160 where little to no reflective material is disposed.
It is understood that embodiments presented herein are meant to be exemplary. Embodiments of the present invention can comprise any combination of compatible features shown in the various figures, and these embodiments should not be limited to those expressly illustrated and discussed.
Although the present invention has been described in detail with reference to certain preferred configurations thereof, other versions are possible. Therefore, the spirit and scope of the invention should not be limited to the versions described above.
This application is a continuation of and claims the benefit of U.S. patent application Ser. No. 13/189,535 filed Jul. 24, 2011, the contents of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 13189535 | Jul 2011 | US |
| Child | 17032252 | US |
