This is directed to a LED light fixture having a shaped light guide array with a CPC reflector for directing light off-axis, and methods for constructing the same. A LED light fixture includes a LED module providing light and an elongated light guide array placed adjacent to the LED module. The elongated light guide array can include a curved outer surface through which light is emitted into an environment. To further control the output of light, and to direct light off-axis, the light guide array can include a CPC reflector disposed around a boundary or periphery of the light guide array. The CPC reflector can be angled such that light is directed at angles above a cut-off angle by which the reflector is rotated about a focus.

BACKGROUND

Light fixtures provide a source of light to illuminate dark environments. A light fixture can be constructed from a light source placed in contact with a light guide for directing light from the light source into an environment. To improve the efficiency of the light fixture, and to reduce costs associated with illumination, a light emitting diode (LED) module can be used as a light source. A LED module, however, emits light that must be re-directed off an axis of the LED module to provide sufficient uniform illumination for a dark environment, such as a garage.

SUMMARY

An edge-lit LED-based light fixtures having a shaped light guide array with a compound parabolic concentrator (CPC) reflector and methods for creating the same are provided. In particular, a light fixture can include a LED light source connected to one end of an elongated and curved light guide array such that light emitted by the LED light source can be frustrated out of the light guide array at different angles to provide uniform luminance. In some cases, the light guide array can incorporate a CPC reflector to redirect a portion of the light flux emitted by the LED light source.

A LED light fixture can include a LED module serving as a light source. To guide the light towards an environment, a light guide array (LGA) can be coupled to the light source such that light from the light source can be redirected towards the environment in a substantially Lambertian distribution. In particular, the LGA can include ribs or other features for frustrating light out of the LGA and into the environment of the fixture.

In some cases, however, it may be desirable for the illumination provided by the LED light fixture to be modified and directed off of the axis of the LED light fixture. In such cases, the LGA can be shaped to include curved surfaces that extend across several different planes. In this manner, light frustrated by the LGA can be redirected at a variety of angles relative to an axis of the LGA to more uniformly illuminate an environment.

To further enhance the illumination pattern provided by the fixture, the LGA can include a CPC reflector incorporated on top of the LGA. The CPC reflector can include a parabolic feature or structure forming a secondary reflective surface that can redirect some of the light emitted by the LED module to an off-axis elevation and azimuth of a desired specification. The position and size of the parabolic features can be selected based on a desired cut-off angle at which off-axis light is directed, and the amount of light flux to be redirected by the parabolic surface or by other features of the LGA. In some cases, features within the light guide can be distributed in different densities to further control the frustration of light in the LGA so as to coordinate with the desired reflection characteristics of the CPC.

DETAILED DESCRIPTION

This is directed to an edge-lit LED light fixture having an elongated light guide array (LGA) to which a LED light source is coupled at a first end. The LGA can be curved such that a surface of the LGA extends over several planes. In some cases, the LGA can include a CPC reflector for further changing an orientation at which light is emitted by the LGA.

A light fixture that uses a LED module as a light source can be mounted in several different manners. In some cases, a light fixture can be mounted to a ceiling, mounted under a counter, as part of a desk light, as a wall sconce, as a wall wash, as a surface mounted light fixture, or combinations of these. Light emitted by the LED module can be directed into the environment from the fixture by a light guide array (LGA).FIG. 1is a side view of an illustrative light fixture in accordance with some embodiments of the invention. Fixture100can include LED module102providing light from light emitting surface104. Emitted light105propagates through light guide array110(LGA110) positioned adjacent to LED module102. LGA110can include an extended structure defined such that light provided into the LGA is directed into the environment through one surface of the LGA. For example, LGA110can include an elongated body such that light is directed out of top boundary116of LGA110, but not out of bottom boundary118of LGA110.

LED module102can provide light to LGA110using different approaches. In particular, LED module102may be placed in contact with or adjacent to first end112of LGA110such that light enters LGA110from first end112and is propagated towards second end114. Light105entering LGA110can be reflected (e.g., totally internally reflected) in part by upper boundary116and lower boundary118. In some cases, reflective component120(e.g., a separate reflective element offset from lower boundary118) can be applied to or near lower boundary118to reflects back scatter off frustration features of surface116and reduce losses of light leaving LGA110through lower boundary118. Some portions106of light105, however, may be frustrated by ribs or other features incorporated in LGA110, such that portions106of light105leave LGA110through upper boundary116. These portions106may serve to illuminate the environment in which fixture100is placed. Portions106can exit LGA110at any angle relative to axis130of LED module102including, for example, at an angle substantially perpendicular to axis130. In some cases, however, the angle may be determined from features within LGA110for frustrating light, from the material of LGA110, or combinations of these.

LGA110can include any suitable waveguide for guiding light waves from a source into an environment. In some cases, LGA110can include a slab or planar waveguide, a rib waveguide, or any other type of waveguide. In some cases, LGA110can include several guides combining to redirect light from a LED module.

LGA110can have any suitable size or shape. In some cases, the size and shape used for a particular

LGA can vary based on the desired use of a light fixture. For example, LGA110can substantially define a rectangular prism having sides that are constrained within planes. Adjacent sides of the LGA can be provided at substantially right angles. The rectangular prism can have any suitable dimensions including, for example, a height of 150 mm (e.g., 6″), a width of 5 mm (e.g., 0.2″) and a length in the range of 300 mm to 2500 mm (e.g., 1′ to 8′). In some cases, LGA110can include a non-rectangular three-dimensional shape. For example, LGA110can include a triangular prism, or any other non-rectangular polygonal prism.

Some environments, such as garages, may require a light fixture that provides light off-axis in a uniform manner. For such uses, a rectangular prism-shaped LGA may not re-direct light in a sufficiently uniform manner. Instead, it may be desirable for the LGA to be shaped such that an elongated surface of the LGA is curved and extends over several planes. In particular, the LGA may be shaped such that a section of the LGA defines a spline.FIG. 2is a side view of a shaped light fixture in accordance with some embodiments of the invention. Light fixture200can include LED module202and LGA210having some or all of the features of light fixture100(FIG. 1). LGA210can include a base structure having first end212adjacent to source204of LED module202, upper boundary216through which light may escape LGA210, and lower boundary218adjacent to which reflecting component220is placed.

In contrast with the light guide of fixture100, however, LGA210may define curved boundary216, such that light206frustrated by features (eg, ribs) on LGA210is emitted at different angles relative to axis230of LED module202. The shape of LGA210can be customized for a particular environment, such that the distribution and angles of light206corresponds to different regions of the environment. In some cases, the shape of LGA210can be defined as a spline that is projected along a vector to create a surface. For example, spline232can be projected along axis234to create a surface at boundary216of LGA210. In some cases, upper boundary216and lower boundary218may be substantially parallel to provide boundaries for rays that are not frustrated by surface features of LGA210.

To further improve the distribution of light by LGA210, the LGA can include a surface corresponding to a CPC reflector in some regions of the LGA.FIG. 3is a diagram of a radiation pattern provided by a shaped LGA having an integrated CPC reflector in accordance with some embodiments of the invention. Pattern300can include several lobes310,320and330extending at different angles relative to axes302and304, where axis302is within the plane of the LGA, and axis304is perpendicular to the plane of the LGA and directed towards the environment.

Center lobe310can extend substantially along axis304into the environment of the light fixture. In some cases, light corresponding to center lobe310can be provided by a primary surface of the LGA (e.g., a surface that does not correspond to a CPC reflector). Lobe310can correspond to any suitable type of radiation including, for example, Lambertian radiation generated by the LGA.

Side lobes320and330can extend at angles relative to axis302. In particular, side lobe320can be defined such that side lobe320extends between axis302and cut-off axis306a, which is angled at angle308arelative to axis302. Similarly, side lobe330can be defined such that side lobe330extends between axis302and cut-off axis306b, which is angled at angle308brelative to axis302. Angles308aand308bcan be the same or different, for example based on the environment in which the LGA is placed.

The particular angles308aand308bcan be determined from attributes of CPC reflectors providing secondary surfaces reflecting LGA flux. Angles308aand308bcan serve as cut-off angles changing the orientation at which the LGA illuminates an environment. In particular, the flux can be steered to elevations between axis302and cut-off axes306aand306b. This may improve the off-axis illumination of the LGA.

FIG. 4Ais a sectional view of an illustrative LGA having a CPC reflector forming a secondary reflective surface in accordance with some embodiments of the invention.FIG. 4Bis a top view of the illustrative LGA ofFIG. 4Ain accordance with some embodiments of the invention. LGA400can include base402having central section410defining primary surface404of the LGA. CPC reflectors420,425,430and435can be distributed around periphery406of base402(e.g., forming a closed loop of CPC reflectors). Each reflector can define a shape of a partial parabola angled relative to primary surface404. The outer surface of each reflector can define a secondary reflective surface for redirecting a beam to off-axis elevations and azimuths, as determined from the angle of the reflector relative to a plane of the primary light source. In some cases, each reflector can instead replace a parabolic section with a hyperbolic section combined with a collimating lens.

The shape of each reflector can be defined by an origin (e.g., points440and448), an axis (e.g., axes450and458), and a width. The parabolas can be defined such that the origins fall within LGA400, along an edge of LGA400(e.g., on periphery406or along an edge of LGA400), or outside of LGA400. In some cases, a reflector can be shaped such that the origin is at an edge or within the LGA. Using this approach, light frustrated at the origin (e.g., at point440or448) can be directed substantially entirely by the CPC reflector (e.g., by reflector420or430, respectively) at an off-axis elevation (e.g., corresponding to side lobes320and330,FIG. 3).

Light frustrated in region444of LGA400between reflectors, for example frustrated at primary surface404, can be directed in a direction substantially normal to primary surface404(e.g., corresponding to primary lobe310,FIG. 3). Light frustrated by region442of LGA400that is between point440and region444can be partially reflected by secondary surface408corresponding to reflector420, and the remainder transmitted without reflecting, contributing to node310inFIG. 3. Similarly, light frustrated by region446of LGA400that is between point448and region444can be partially reflected by secondary surface409corresponding to reflector430and the remainder transmitted with reflecting, contributing to node310inFIG. 3.

In effect, light emitted by portions of primary surface404that are underneath a reflector may be redirected by the secondary surface at an angle that is bound by a sharp cut-off at an angle or elevation corresponding to the CPC reflector. This approach may allow precise control of the flux and beam shaping for modest to extreme off-axis elevations and azimuths.

The size and position of the reflectors relative to the primary surface within the reflectors can be tuned for performance in a particular environment. For example, by extending the reflector in-board from the periphery of the LGA, more of the flux can be captured and redirected off-axis. Alternatively, if the reflector is moved out-board towards the periphery of the LGA, less flux may be captured by the reflector and the LGA may provide a more direct light along an axis of the LGA.

In some cases, the base or reflectors of LGA400can include internal features for frustrating light out of the LGA and into the environment. For example, the LGA can include several ribs distributed within the LGA at various intervals for frustrating light.FIG. 5Ais top view of an illustrative LGA in accordance with some embodiments of the invention.FIG. 5Bis a detailed view of a portion of the LGA ofFIG. 5Ain accordance with some embodiments of the invention. LGA500can include base510and CPC reflectors520,525,530and535disposed around periphery506of LGA500. Portion540of LGA500, shown inFIG. 5B, can include a portion of reflector520and a portion of base510.

Each of reflector520and base510can include features for frustrating light emitted by a light source. In the example ofFIG. 5B, the features can correspond to ribs extending along a length of reflector520and base510. For example, reflector520can include ribs550, and base510can include ribs552. Based on the frequency or density of ribs, the amount of light frustrated by each portion of LGA500can vary.

To control the amount of light provided by each of reflector520and base510, the number or density of ribs in each portion can be tuned. For example, ribs550and ribs552can be distributed at intervals varied to provide similar light outputs by each of reflector520and base510. As another example, ribs550and ribs552can be distributed at different intervals (e.g., such that ribs550are closer to each other than ribs552, or vice versa) to direct more or less light out of reflector520relative to base510. In some cases, the space between adjacent ribs in one or both of base510and reflector520can vary. In the example of LGA500, the distance between ribs550may increase from outer boundary522of reflector520towards interface524between reflector520and base510. In addition, the distance between ribs522in base510can increase from interface524towards a center of base510. This approach can ensure that light is evenly distributed in each of the lobes depicted in light pattern300(FIG. 3).

A LGA having a curved surface and a CPC reflector can be constructed using different approaches. In some cases, different features of the LGA can be cut from a block of material (e.g., using a machining process). Alternatively, the LGA can be molded (e.g., injection molded, compression molded, or vaccum formed) with desired features. In some cases, one or more surfaces of the LGA can be processed to improve their reflectivity. For example, the surfaces of the LGA can be polished (e.g., using an abrasive tool).

The LGA can be constructed from any suitable material. In some cases, the material used can be selected such that the index of refraction between the material and air is approximately 1.5. Such materials can include, for example, an acrylic, polycarbonate, glass, or another plastic material that is substantially transparent.

FIG. 6is a flow chart of an illustrative process for constructing a light guide array having a CPC reflector in accordance with some embodiments of the invention. Process600can begin at step602. At step604, a shaped light guide array can be provided. For example, an optically transparent material can be retrieved and shaped to fit in a light fixture. In some cases, the material can be provided substantially as a rectangular prism that includes a curved surface. At step606, a secondary surface corresponding to a reflector can be defined on the light guide array. For example, a parabolic shape corresponding to a CPC reflector can be defined in the LGA, where the axis of the parabolic shape can be selected to provide off-axis illumination using the light guide array. In some cases, material can be cut away from a base structure to form the secondary surface. The light guide array can include any suitable number of secondary surfaces corresponding to reflectors including, for example, four secondary surfaces corresponding to four reflectors positioned around four sides of the LGA. At step608, the light guide array can be polished to improve the reflectivity of the light guide array. Alternatively, a diffusive layer can be placed over one or both of the primary surface and the secondary surface. In some cases, other finishing processes can be applied to the LGA, or step608can be skipped. Process600can then end at step610.

It is to be understood that the steps shown in process600ofFIG. 6are merely illustrative and that existing steps may be modified or omitted, additional steps may be added, and the order of certain steps may be altered. Insubstantial changes from the claimed subject matter as viewed by a person with ordinary skill in the art, now known or later devised, are expressly contemplated as being equivalently within the scope of the claims. Therefore, obvious substitutions now or later known to one with ordinary skill in the art are defined to be within the scope of the defined elements.

The above-described embodiments of the invention are presented for purposes of illustration and not of limitation.