Patent Application
20120262902
Light emitting diode (LED) lighting systems are becoming more prevalent as replacements for existing lighting systems. LEDs are an example of solid state lighting (SSL) and have advantages over traditional lighting solutions such as incandescent and fluorescent lighting because they use less energy, are more durable, operate longer, can be combined in red-blue-green arrays that can be controlled to deliver virtually any color light, and contain no lead or mercury. In many applications, one or more LED dies (or chips) are mounted within an LED package or on an LED module, which may make up part of a lighting unit, lamp, “light bulb” or more simply a “bulb,” which includes one or more power supplies to power the LEDs. An LED bulb may be made with a form factor that allows it to replace a standard threaded incandescent bulb, or any of various types of fluorescent lamps. LEDs can also be used in place of florescent lights as backlights for displays.
Color reproduction can be an important characteristic of any type of artificial lighting, including LED lighting. For lamps, color reproduction is typically measured using the color rendering index (CRI). The CRI is a relative measurement of how the color rendition of an illumination system compares to that of a particular known source of light. In more practical terms, the CRI is a relative measure of the shift in surface color of an object when lit by a particular lamp. The CRI equals 100 if the color coordinates of a set of test surfaces being illuminated by the lamp are the same as the coordinates of the same test surfaces being irradiated by the known source. CRI is a standard for a given type light or light from a specified type of source with a given color temperature. A higher CRI is desirable for any type of replacement lamp.
To achieve accurate color, wavelength conversion material is sometimes used in lighting systems. The wavelength conversion materials may produce white light when struck by light of a specified color, or may produce an additional color of light that mixes with other colors of light to produce white light, or another specific desired color of light. As an example, phosphor particles can be used as a wavelength conversion material. Phosphor absorbs light at one wavelength and re-emits light at a different wavelength. Typically, phosphor particles are randomly distributed within the matrix of encapsulant material. The term phosphor can refer to materials that are sometimes also referred to as fluorescent and/or phosphorescent. Most phosphors absorb light having low wavelengths and re-emit light having longer wavelengths.
Embodiments of the invention provide for a solid state luminaire or light fixture using GaN-based LEDs, for example, LEDs with an InGaN active layer. The LEDs ultimately illuminate and activate a thin or dilute remote phosphor coating applied to a reflective substrate formed to act as a reflector for the fixture. Using a thinner or more dilute layer of remote phosphor can reduce phosphor cost. In some embodiments, the GaN LEDs are also packaged with a phosphor so that less intense blues are produced by the LED devices. In some embodiments, GaN LED devices are used exclusively, so that the luminaire does not need to be engineered to take into account the different thermal profiles and colors of GaN and GaP LEDs, the latter of which typically produces red light. Thus, in some embodiments of the invention a lighting system is provided where an LED light source and a remote phosphor are selected and positioned to provide indirect light as substantially white light.
In some embodiments, the luminaire includes an LED light source and a reflector disposed to reflect light from the LED light source and direct light out of the luminaire to provide illumination. A thin or dilute layer of phosphor is applied to the reflector to provide wavelength conversion for at least a portion of the light from the light source. The luminaire emits substantially white light. In some embodiments, the LED light source includes at least one LED with a GaN emitting layer.
In some embodiments, the phosphor layer on the reflector is between 5 and 50 μm thick. In some embodiments, the phosphor layer is between 5 and 25 μm thick. In some embodiments, the LEDs with the GaN emitting layer are packaged with a local phosphor as blue-shifted yellow (BSY), blue-shifted green (BSG), blue-shifted red (BSR) or cyan-shifted red (CSR) LED devices. LEDs emitting a specific color without local phosphor can also be used. In some embodiments LEDs emitting blue, royal blue or cyan light can be included in the luminaire. In some embodiments, the phosphor includes red, red/orange, yellow, green or cyan emitting phosphor. In some embodiments, the phosphor includes at least two, different color emitting phosphors.
A luminaire according to embodiments of the invention can take many different forms. In some embodiments, the luminaire is a light fixture using a plurality of GaN-based LED devices as the light source. The LED devices can be positioned on a mounting surface of a heatsink, wherein the mounting surface is positioned opposite a reflector with the phosphor applied. In some embodiments, the reflector includes two parabolic regions. In some embodiments, the reflector has a flat region opposite the mounting surface of the heatsink. In some embodiments, the fixture includes a diffuser lens assembly.
This diffuser lens assembly can include two lens plates disposed at the sides of the heatsink. In some embodiments, the fixture includes a pan to support the fixture when mounted in a ceiling. The light fixture can be assembled by providing a housing including the reflector and then coating the reflector with a phosphor to the desired thickness. The light source and heatsink assembly are positioned so that light from the GaN LED light source impinges on the reflector with the phosphor. The diffuser assembly can be positioned adjacent to the heatsink so that light from the GaN LED light source and the phosphor leaves the light fixture through the diffuser lens assembly.
Embodiments of the present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.
It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the present invention. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
It will be understood that when an element such as a layer, region or substrate is referred to as being “on” or extending “onto” another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or extending “directly onto” another element, there are no intervening elements present. It will also be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.
Relative terms such as “below” or “above” or “upper” or “lower” or “horizontal” or “vertical” may be used herein to describe a relationship of one element, layer or region to another element, layer or region as illustrated in the figures. It will be understood that these terms are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and/or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Unless otherwise expressly stated, comparative, quantitative terms such as “less” and “greater”, are intended to encompass the concept of equality. As an example, “less” can mean not only “less” in the strictest mathematical sense, but also, “less than or equal to.”
As previously mentioned, embodiments of the invention provide for a solid state luminaire or light fixture using GaN-based LEDs. The LEDs ultimately illuminate and activate a thin or dilute remote phosphor coating applied to a reflective substrate formed to act as a reflector for the fixture. Using a thinner or more dilute layer of remote phosphor can reduce phosphor cost. The GaN LEDs can also be packaged with a phosphor so that less intense blues are produced. If GaN LED devices are used exclusively, the luminaire does not need to be engineered to take into account the different thermal profiles and colors of GaN and GaP LEDs, the latter of which typically produce red light.
As examples of embodiments of the invention described herein, a lighting system is shown as a light engine for a troffer-style light fixture. The lighting system includes the remote reflector with a phosphor layer applied as well as the LED light source. The troffer-style light fixture is shown as an example luminaire. Such a luminaire might be used as a solid-state replacement for a standard fluorescent light fixture, and/or might be of a form factor to be placed in the space normally occupied by a drop ceiling tile in an office environment. Various combinations of LEDs and phosphors will be discussed. Any of these, and others, can be used to produce substantially white light from the system. It cannot be overemphasized that all of these detailed embodiments are provided as examples only, and that a luminaire, lighting system or fixture that implements an embodiment of the invention can take many forms and be made in many ways. An embodiment of the invention can be developed based on the disclosure herein for any type of directional solid-state lighting. For example, an embodiment of the invention could be used to create a solid-state replacement for a standard R30 incandescent bulb that is commonly used in residential down-lighting.
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To further explain what is meant herein by “substantially white” light, the color of light can be indicated in a chromaticity diagram, such as the 1931 CIE Chromaticity Diagram. Such a diagram includes a blackbody locus of points, which indicates points in the color space for light that humans perceive as the same or close to natural sources of light. A good “white” light source is generally considered a source whose point in the color space falls within four MacAdam ellipses of any point in the blackbody locus of points. In some embodiments of the present invention, this distance can be achieved. However, if the point for the light from a luminaire according to embodiments of the invention falls within six MacAdam ellipses in some embodiments or ten MacAdam ellipses in some embodiments, such light would be considered substantially white light for purposes of this disclosure. Further discussion of CIE diagrams and the blackbody locus of points can be found in U.S. Pat. No. 7,768,192, which is incorporated herein by reference.
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In addition to the blue-shifted yellow plus red (BSY+R) system already discussed, other combinations of LEDs and phosphor can be used to implement an embodiment of the invention, and produce substantially white light. Other colors of light can be produced as well. LED packages can be used to emit blue-shifted green (BSG) light by using a blue LED as already described with a phosphor emitting green light, that is, a phosphor emitting light with a wavelength in the range of 510-550 nm. A red-emitting phosphor can be packaged with such an LED to form a blue-shifted red (BSR) light source. A red-emitting phosphor can be packaged with a cyan emitting LED as the light source. The cyan emitting LED structure emits light in the wavelength range of 480 to 510 nm, or 487 to 505 nm. Such a light source can be considered a cyan-shifted red (CSR) light source. A royal blue emitting LED can be added to the system, packaged either alone or with a phosphor. A royal blue LED emits light having a wavelength in the upper portion of the wider blue wavelength ranges already discussed, or from about 466 to 486 nm. Appropriate adjustments to the phosphor on the reflector of the light engine of an embodiment of the present invention are made depending on the type of LEDs used, whether they are packaged with a phosphor, and the wavelength emitted by both phosphors.
In addition to color combinations already discussed, some example combinations of LEDs with and without local phosphors and specified color-emitting phosphors for the reflector for a light engine according to embodiments of the invention will now be described. The red remote phosphor already described with BSY LED packages can also be used with BSY and cyan LED packages, or BSY and royal blue LED packages, where the cyan and royal blue LEDs are packaged without a local phosphor. A red and spatially separated cyan phosphor or a red and spatially separated green phosphor can be used on the reflector with BSY LED devices. Where spatially separated different color phosphors are used, they can be applied to the reflector in any of various patterns, including alternating stripes, in a pixilated pattern, or in alternating blocks.
BSG devices can be used alone as a light source with a red/orange remote phosphor on the reflector, or can be combined with either royal blue or cyan LED devices and used with the red/orange remote phosphor. A BSG light source can also be used with a reflector including red/orange and a spatially separated cyan or yellow phosphor. BSR devices can be used alone as a light source with a yellow remote phosphor on the reflector, or can be combined with either royal blue or cyan LED devices and used with the yellow remote phosphor. A BSR light source can also be used with a reflector including yellow and a spatially separated cyan or green phosphor. CSR devices can be used alone as a light source with a yellow remote phosphor on the reflector, or can be combined with either royal blue or cyan LED devices and used with the yellow remote phosphor. CSR and blue devices can be used with a reflector including yellow and a spatially separated green phosphor.
A light source used with example embodiments of the invention can also used multiple types of devices packaged with local phosphors. For example, BSY and CSR LED devices can be used together with a green-emitting phosphor on the reflector, as can BSY and BSR devices. BSY and BSR devices can also be used with cyan phosphor on the reflector, or with spatially separated cyan and green phosphors on the reflector. Additionally, mixed phosphors on the reflector need not be spatially separated. Phosphors emitting two or more different colors can simply be mixed together to produce a desired color profile. A luminaire can also be produced using only specific color-emitting LEDs packaged without local phosphor so that most of the light from the active layers of the LEDs directly energizes the phosphor(s) on the reflector, with the colors all tuned to produce a desired color of light using the indirect light of the LEDs. As an example, blue emitting LEDs could be used as the light source and a mixture of red and green phosphor can be used on the reflector to produce substantially white light as previously described.
The combinations of LED devices with phosphorized reflectors given as examples above can be used to create various colors of light, including substantially white light with a color rendering index (CRI) at least as good as generated by relatively low CRI types of residential lighting. Example embodiments can produce light with a CRI of at least 70, at least 80, at least 90, or at least 95. Again, by use of the term substantially white light, one could be referring to a chromacity diagram including a blackbody locus of points, where the point for the source falls within four or six or ten MacAdam ellipses of any point in the blackbody locus of points.
Embodiments of the invention can use varied fastening methods and mechanisms for interconnecting the parts of the lighting system and luminaire. For example, in some embodiments locking tabs and holes can be used. In some embodiments, combinations of fasteners such as tabs, latches or other suitable fastening arrangements and combinations of fasteners can be used which would not require adhesives or screws. In other embodiments, adhesives, screws, bolts, or other fasteners may be used to fasten together the various components.
Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art appreciate that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiments shown and that the invention has other applications in other environments. This application is intended to cover any adaptations or variations of the present invention. The following claims are in no way intended to limit the scope of the invention to the specific embodiments described herein.
