Patent Application
20130265760
1. Field of the Invention
The invention relates generally to optical assemblies for lighting applications and, more particularly, to variable beam angle fixture assemblies for solid state 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 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 a 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.
Recent lighting luminaire designs have incorporated LEDs into lamp modules. There are several design challenges associated with the LED-based lamp modules including: source size, heat management, overall size of the lamp assembly, and the efficiency of the optic elements. Source size is important because the size of a 2 pi emitter dictates the width of the output beam angle (i.e., etendue) using a standard aperture, such as a 2 inch (MR16) aperture, for example. Heat dissipation is a factor because, as noted above, the junction temperature of LEDs must be kept below a maximum temperature specified by the manufacturer to ensure optimal efficacy and lifetime of the LEDs. The overall size of the optical assembly is important because ANSI standards define the physical envelope into which a lamp must fit to ensure compliance with standard lighting fixtures. Lastly, the efficiency of the optic elements must be high so that the output from high-efficacy LEDs is not wasted on inefficient optics.
To address the issue of overall optical assembly size, total internal reflection (TIR) lenses have been used in lamp packages. In many implementations, additional beam-shaping optics are attached to the TIR with a lens carrier. The lens carrier may be attached to the TIR using various methods such as a two-piece trap or heat staking, for example. The TIR/lens carrier component requires early configuration in the assembly process. Additionally, customers cannot easily adjust these lamps for different beam-angle outputs. Each light source is associated with a collimator to collimate light as it is initially emitted from the source.
An embodiment of a directional lighting system comprises the following elements. A collimator is within a housing. A removable transmissive cover is proximate to the collimator. The cover comprises micro lenses shaped to determine an outgoing beam angle.
An embodiment of a directional lighting system comprises the following elements. A housing comprises a base. At least one light source is on a mount surface of the base. A collimator is arranged to receive light emitted from the light source and collimate the light. A removable cover is proximate to the collimator. The cover comprises micro lenses shaped to determine the beam of angle of light exiting the open end of the housing.
An embodiment of a fixture assembly comprises the following elements. A housing defines an interior cavity and an open end and comprises a base. A plurality of light emitting diodes (LEDs) is on a mounting surface of the base in the cavity. A plurality of collimators is in the cavity, each of the collimators arranged to collimate light from at least one of the LEDs toward the open end of the housing. A removable cover is on the open end of the housing, the removable cover comprising micro lenses shaped to determine the beam angle of light exiting the open end of the housing.
Embodiments of the present invention provide a directional lighting fixture having a variable beam angle that is easily adjusted. A fixture housing is shaped to define an interior cavity and an open end. One or more lighting sources are disposed within the cavity. A removable transmissive cover is disposed over the open end of the housing. The cover comprises a micro lens structure that defines the beam angle of the light that is emitted from the fixture. The removable cover can be easily replaced by the end user with a different cover to achieve a desired beam angle.
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. Light of a particular color may also be characterized by a specific combination of discrete wavelengths that, in combination, exhibit the particular color.
The protective housing 106 surrounds the collimators 102 and the sources 104 to shield these internal components from the elements. A portion of the housing 106 may comprise a material that is a good thermal conductor, such as aluminum or copper. The thermally conductive portion of the housing 106 can function as a heat sink by providing a path for heat from the sources 104 through the housing 106 into the ambient. In some embodiments the housing 106 can comprise heat dissipating features such as fins or heat pipes. In other embodiments the housing 106 can comprise different types of lamp collars that can be mounted to a different feature such as a separate heat sink. The sources 104 are disposed at the base of the housing 106 in good thermal contact with the body of the housing 106. Thus, the sources 104 may comprise high power LEDs that generate large amounts of heat. Although in this particular embodiment the light sources 104 comprise individual LED components, other embodiments may comprise multi-chip elements such as a chip-on-board (COB) element, for example, as discussed in more detail herein.
Power is delivered to the sources 104 through a protective conduit 110. The fixture 100 may be powered by a remote source connected with wires running through the conduit 110, or it may be powered internally with a battery that is housed within the conduit 110. The conduit 110 may be threaded as shown in
The conduit 110 functions not only as a structural element, but may also provide electrical isolation for the high voltage circuitry that it houses which helps to prevent shock during installation, adjustment, and replacement. The conduit 110 may comprise an insulative and flame retardant thermoplastic or ceramic, although other materials may be used.
A transmissive removable cover 112 may be placed over the collimators 104 at the open end of the housing 106. The cover 112 and the housing 106 may form a watertight seal to keep moisture from entering into the internal areas of the fixture 100. The cover 112 is easily removable and attachable to the open end of the housing 106. Thus, several different covers 112, each having different optical properties, may be used with the fixture 100 to change the appearance of the output beam.
The cover 112 may be removably attached to the housing several different structures. In one embodiment, the cover 112 and housing 106 comprise snap-fit structures so that the cover 112 may be easily removed and reattached to the housing 106. The snap-fit attachment mechanism makes it easy for a vendor or an end user to switch out various covers to produce a desired output effect. It is understood that the cover 112 may be attached to the housing 106 with other mechanisms such as screws, latches, or adhesives, for example.
The cover 112 comprises a micro lens structure 114. The micro lens structures may be distributed across the entire face of the cover 112 or may be confined to specific areas. Additionally, the micro lens structures can be uniform or non-uniform across the face of the cover 112 as discussed in more detail herein. Many different known micro lens structures may be used to achieve an output beam having particular characteristics. For example, the micro lenses 114 may be designed to produce a desired output beam angle (i.e., to control beam divergence). In one embodiment, removable covers 112 comprising different micro lens structures 114 can respectively produce beam angles of 12 degrees, 25 degrees, or 40 degrees, for example. Nearly any desired beam angle can be achieved using different known micro lens structures.
The micro lens structure 114 shown in
The cover 112 comprises a flat outer surface 116 to facilitate maintenance and cleaning. In this particular embodiment, the micro lens structure 114 is uniform and covers the entire area of the cover 112. In other embodiments, it may be more efficient to limit the micro lens structure to a particular area or areas of the cover 112 as discussed in more detail herein.
Because, in this embodiment, most of the collimation is done with the TIR lenses 506, it may be desirable to use a diffuse material on the interior surface of the reflector cups 508. Thus, in embodiments using the TIR lens/reflector cup combination similar to the one shown in
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 LEDs emitting yellow (or blue-shifted 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 coating on the interior surface of the reflector cup 306 in combination with other diffusive elements. In some embodiments, the cup interior 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.
In some embodiments, individual LED sources may be replaced with LEDs that are clustered in a given area(s) using a chip-on-board (COB) configuration as mentioned briefly with reference to
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 configurations thereof, other versions are possible. Therefore, the spirit and scope of the invention should not be limited to the versions described above.
