News Column

Researchers Submit Patent Application, "Tilted Emission Led Array", for Approval

May 21, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Washington, D.C., VerticalNews journalists report that a patent application by the inventors Rol, Fabian (Goleta, CA); Tarsa, Eric (Goleta, CA); Keller, Bernd (Santa Barbara, CA); Lowes, Theodore D. (Lompoc, CA); Emerson, David T. (Chapel Hill, NC), filed on March 15, 2013, was made available online on May 8, 2014.

The patent's assignee is Cree, Inc.

News editors obtained the following quote from the background information supplied by the inventors: "The present disclosure is directed generally to light emitting diodes (LEDs) and more particularly to LED components that can produce a desired light emission profile and these components within a system.

"Light emitting diodes (LEDs) are solid state devices that convert electric energy to light, and generally comprise one or more active layers of semiconductor material sandwiched between oppositely doped layers. When a bias is applied across the doped layers, holes and electrons are injected into the active layer where they recombine to generate light. Light is emitted from the active layer and from all surfaces of the LED.

"Technological advances over the last decade or more have resulted in LEDs having a smaller footprint, increased emitting efficiency, and reduced cost. LEDs also have an increased operation lifetime compared to other light emitters. For example, the operational lifetime of an LED can be over 50,000 hours, while the operational lifetime of an incandescent bulb is approximately 2,000 hours. LEDs can also be more robust than other light sources and can consume less power. For these and other reasons, LEDs are becoming more popular and are being used in applications that have traditionally been the realm of incandescent, fluorescent, halogen and other emitters. Indeed, lighting applications which previously had typically been served by fixtures using what are known as high intensity discharge (HID) lamps are now being served by LED lighting fixtures. Such lighting applications include, among a good many others, roadway lighting, factory lighting, parking lot lighting, and commercial building lighting.

"In many of such products, achieving high levels of illumination over large areas with specific light-distribution requirements is particularly important. One example is fixtures for roadway lighting, an application in which the fixtures are generally placed along roadway edges while light distribution is desired along a significant portion of roadway length and, of course, on the roadway itself--generally to the exclusion of significant light off the roadway. And in such situations it is desirable to minimize the use of large complex reflectors and/or varying orientations of multiple light sources to achieve desired illumination patterns.

"LEDs are also being used in displays, both big and small. Large screen LED based displays (often referred to as giant screens) are becoming more common in many indoor and outdoor locations, such as at sporting events, race tracks, concerts and in large public areas, such as Times Square in New York City.

"Additionally, LEDs are being used in a variety of lighting applications. Some lighting applications require uniform ambient lighting, whereas others require particular beam shapes, emission profiles, or intensity levels. One example of such a use includes street lighting, which requires uniform light output of a particular intensity in a particular beam shape to allow for illumination of only a particular area.

"Present technology utilizes optics and geometries that maximize light extraction from the LED to obtain uniform emission profiles. This usually entails a hemispherical lens coupled to a light emitting element where the optical centers of the lens and the emitting surface are perfectly aligned, and the peak light emission is along the optical axis. However, such a configuration may not be advantageous for all situations, such as when an LED display is mounted above the viewer's eye level or a directed lighting pattern is required, for example in street lighting.

"Referring now to FIGS. 1A and 1B, exemplary LED downlights 10 are shown mounted at an elevated point above a street 12, functioning as a street light. The street 12 area to be lit is typically positioned below the downlight 10 and is at an angle with respect to the downlight's emission direction, which is perpendicular to the downlight surface. When light emission is required at an angle other than the center, as shown in FIG. 1A, light is wasted because secondary optics must be used to redirect the light and secondary optics cause some percentage of loss. FIG. 1A shows unmodified emission pattern. FIG. 1B shows a modified emission pattern using secondary optics. The LED downlight street light as shown in FIG. 1A includes a plurality of emitters, such as an LED package, which may include an LED mounted within the street light housing. Secondary optics must be placed over these LED packages to modify the emission pattern from that shown in FIG. 1A to the pattern shown in FIG. 1B. FIG. 2 shows an exemplary LED package 200, which may be used in the street lights of FIGS. 1A-1B. The LED package 200 includes an array of LED chips 215 on a substrate 205, with a lens 200. As shown, the center CA of the array of LED chips 215 is aligned with the center CL of the lens 220. The peak emission for the LED package 200 is along the package's longitudinal axis. FIG. 3 is a polar iso-candelar graph 30 for the LED package 200, showing the peak emission along the emitter's longitudinal axis.

"FIG. 1A shows a light fixture 10 comprising a plurality of LED packages 200 emitting with characteristics that display a peak emission directed along a perpendicular direction. The intensity profile (Iv) and far field pattern (FFP) peak emission characteristics for the downlight 10 are also perpendicular to the fixture along the perpendicular axis.

"One way to reduce the amount of light that is wasted is by mounting the light emitters at an angle to better match the desired illumination area or viewer's line of sight, but this can require complex and expensive mounting configurations or hardware that is difficult to use. Efforts have also been made to control the light emission from LED packages by modifying the shape of the encapsulant or lens, but this may require special, costly lens tooling and complex lens fabrication processes. Some systems may utilize secondary optics to alter beam profiles or redirect light patterns to different angles; however, the secondary optics may cause significant losses on the order of 10-12% and add cost to the display system."

As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "The present invention is directed to LED components with primary optics providing improved emission characteristics. The present invention is also directed to light fixtures utilizing the LED components to provide improved light fixture emissions.

"One configuration describes, a light emitting diode (LED) component system comprising a housing and a plurality of LED components within the housing, such that light emitted from the housing has a peak emission shifted from a perpendicular centerline of the housing. Each of the plurality of LED components comprises at least one LED chip on a mounting surface and an optical lens overlying the LED chip and having a lens base attached to the mounting surface. The LED chips are positioned to provide a peak emission shifted from a perpendicular centerline of the lens base.

"Another configuration includes, a light emitting diode (LED) component system comprising a housing and a mounting board within the housing. The system further includes a plurality of LED components on the mounting board, such that light emitted from the housing has a peak emission shifted from a perpendicular centerline of the housing. Each of the plurality of LED components comprises at least one LED chip on the mounting board and an optical lens overlying at least one LED chip. The optical lens has a lens base on a side of the lens adjacent to at least one LED chip.

"These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate by way of example the features of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

"FIG. 1A is a top view of a prior art overhead street light and emission pattern on a street;

"FIG. 1B is a top view of another prior art overhead street light downlight and a modified emission pattern on a street;

"FIG. 2 is a top view of a LED Package;

"FIG. 3 is polar iso-candelar graph showing the light emission characteristics of the LED package in FIG. 2;

"FIG. 4A is a perspective view of an exemplary LED component including an array of LED chips on a monolithic substrate with a single overlying lens;

"FIG. 4B is a top view of the LED component of FIG. 4A showing the offset between the center CA of the array of LED chips and the center CL of the lens base of the overlying lens;

"FIG. 5A is a cross-sectional view of a portion of an exemplary array of LED chips on a monolithic substrate where a plurality of the LED chips exhibit a tilt .tau. with respect to the perpendicular centerline;

"FIG. 5B is a cross-sectional view of a portion of another exemplary array of LED chips on a monolithic substrate where the LED chips exhibit different tilts .tau.1 and .tau.2;

"FIG. 6 is a top view of an exemplary LED component including an LED array having a subsection displaced to a different region of the substrate;

"FIG. 7 is a top view of an exemplary LED component including two LED arrays, each array having a center displaced with respect to the center CL of the lens base;

"FIG. 8A is a perspective view of an exemplary LED component including an array of LED chips on a monolithic substrate where each LED chip includes an overlying lens;

"FIG. 8B is a cross-sectional view of the LED component of FIG. 8A;

"FIG. 8C is a top view of the LED component of FIG. 8A;

"FIG. 8D is a close-up view of a portion of FIG. 8C showing the offset d between the center of the LED chip and the center CB of the lens base;

"FIG. 9 is a top view of an exemplary LED component including two arrays of lenses having centers CLA1, CLA2 that are offset with respect to the center CS of the submount, where each lens overlies an LED chip that may be centered or offset with respect to the center CB of the respective lens base;

"FIG. 10 is a cross-sectional view of a portion of an LED component including an array of LED chips with overlying lenses and a combination of tilts and displacements;

"FIG. 11 is a schematic showing a stamping process that may be employed to fabricate an angled landing pad for mounting an LED chip at an angle .gamma. to the surface of the submount;

"FIGS. 12A-12C are schematics showing how a stamping process may be applied directly to a submount to create angled protrusions and depressions in the frontside and backside surfaces of the submount;

"FIG. 13A is a photograph of an exemplary LED component that includes 12 LEDs, each with its own hemispherical lens;

"FIG. 13B includes a chart showing normalized intensity as a function of angle from the perpendicular centerline, where the data is obtained for three embodiments of the LED component of FIG. 13A, as indicated in FIGS. 13C-13E;

"FIGS. 13C-13E show an LED chip at the optical center of a hemispherical lens (FIG. 13C); an LED chip offset radially inward (FIG. 13D); and an LED chip offset radially outward (FIG. 13E);

"FIG. 14A is a top view of an exemplary LED component including a 2.times.2 array of LED chips; and

"FIG. 14B is a chart showing the shift in the intensity profile that occurs depending on the amount of displacement between the center of the LED chip array of FIG. 14A and the center of the lens base;

"FIG. 15A is a perspective view of an exemplary LED component including an array of LED chips and an array of optical lenses on a monolithic substrate, where the number of LED chips exceeds the number of lenses and where each of the lenses overlies a plurality of LED chips;

"FIG. 15B is a close-up view of a portion of FIG. 15A showing the offset d between the center CA of the plurality of LED chips and the center CB of the lens base;

"FIG. 16 a cross-sectional view of a portion of an LED component including an array of optical lenses where each lens overlies one or more LED chips, and further where some of the lenses have an asymmetric shape;

"FIGS. 17A-F are cross-sectional views of an LED component showing a range of progressively larger offsets between the center CA of the plurality of LED chips and the center CL of the lens base;

"FIGS. 18A-F are graphs showing the intensity slice data for each of the respective offsets in FIGS. 17A-F;

"FIGS. 19A-F are graphs showing the maximum tilt intensity slice data for each of the respective offsets in FIGS. 17A-F;

"FIGS. 20A-F are graphs showing the normalized intensity slice data for each of the respective offsets in FIGS. 17A-F;

"FIGS. 21A-F are side views of the LED components of FIGS. 17A-F demonstrating ray tracing results for each of the respective offsets in FIGS. 17A-F;

"FIG. 22A is a graph with associated table of points demonstrating the relationship between efficiency and tilt of an LED component in relation to the offset size;

"FIG. 22B is a graph and associated equation for such a graph demonstrating the relationship between efficiency and offset of the light emitter;

"FIG. 22c is a graph and associated equation for such a graph demonstrating the relationship between tilt and offset of the light emitter;

"FIG. 23 shows another configuration of an LED component utilizing an offset to provide a tilted emission;

"FIGS. 24A-F are cross-sectional views of the LED component of FIG. 23 showing a range of progressively larger offsets between the center CA of the plurality of LED chips and the center CL of the lens base;

"FIGS. 25A-F are graphs showing the intensity slice data for each of the respective offsets in FIGS. 24A-F;

"FIGS. 26A-F are graphs showing the maximum tilt intensity slice data for each of the respective offsets in FIGS. 24A-F;

"FIGS. 27A-F are graphs showing the normalized intensity slice data for each of the respective offsets in FIGS. 24A-F;

"FIGS. 28-34 show different configurations of systems which employ the LED components shown in various other figures;

"FIG. 35 is a graph and associated equation for such a graph demonstrating the relationship between tilt angle and offset over lens diameter of two light emitters with different widths; and

"FIG. 36 is a graph and associated equation for such a graph demonstrating the relationship between normalized efficiency and offset over lens diameter of two light emitters with different widths."

For additional information on this patent application, see: Rol, Fabian; Tarsa, Eric; Keller, Bernd; Lowes, Theodore D.; Emerson, David T. Tilted Emission Led Array. Filed March 15, 2013 and posted May 8, 2014. Patent URL: http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=5972&p=120&f=G&l=50&d=PG01&S1=20140501.PD.&OS=PD/20140501&RS=PD/20140501

Keywords for this news article include: Cree Inc., Electronics, Light-emitting Diode.

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Source: Electronics Newsweekly


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