Patent Application
20120268915
The present invention relates to geometry for producing generally lateral and downward-propagating white-light illumination, using solid state lighting sources and a phosphor located away from the solid state lighting source.
Solid state light sources, such as but not limited to light emitting diodes (LEDs), organic LEDs (OLEDs), and the like, have significant advantages over conventional incandescent light sources. These include lower power requirements and longer lifetime. Unlike typical incandescent light sources, which radiate light generally uniformly in all directions, a solid state light source has a light output that is generally directional. Such directionality may offer newfound flexibility in producing illumination systems that have tailored light output.
Embodiments described herein produce white-light illumination in a generally lateral and downward-propagating direction. A module according to embodiments described herein has a longitudinal axis from a downward to an upward direction, and emits white phosphor light generally downward and laterally from the module. A light engine including least one LED chip is mounted on a top surface of a heat sink, emitting excitation light generally upward, typically with a blue wavelength. A conically-shaped lens extends from the heat sink to a top of the module, with the cone having a narrow end at the heat sink and a wide end at the top of the module. The lens reflects upward all or a part of any blue excitation light that strikes it. The upward-traveling blue light is received and absorbed by a funnel-shaped phosphor surface, where the funnel has a narrow end at the heat sink and a wide end at or near the top of the module. The phosphor surface emits phosphor light generally downward and laterally, at a wavelength longer than that of the excitation light. The phosphor light transmits through the lens and exits the module.
In an embodiment, there is provided a light-producing module having a base, a top, a longitudinal axis extending from a center of the base to a center of the top, and a lateral edge surrounding the longitudinal axis. The light-producing module includes: a plurality of solid state light sources disposed at the base of the module emitting excitation light toward the top of the module, the excitation light having at least one excitation wavelength and having an angular distribution centered about the longitudinal axis of the module; a lens defining the lateral edge of the module and extending from the base of the module to the top of the module, the lens reflecting the excitation light; and a phosphor surface receiving and absorbing the excitation light and producing phosphor light, the phosphor surface being shaped as a funnel having a wide end proximate the top of the module and a narrow end proximate the base of the module, the phosphor light having a wavelength greater than the at least one excitation wavelength and having an angular distribution at each point on the phosphor surface centered about a local surface normal with respect to the phosphor surface, the phosphor light exiting the module through the lateral edge defined by the lens.
In a related embodiment, the lens may enclose a gas-filled volume between the phosphor surface and the lateral edge of the module, and the excitation light and the phosphor light may propagate through the gas when inside the module. In a further related embodiment, the phosphor surface may be a funnel element, the funnel element having a narrow end proximate the base of the module and a wide end proximate the top of the module, the plurality of solid state light sources being arranged outside the narrow end of the funnel element, the wide end of the funnel element extending radially outward to the lens. In a further related embodiment, the base of the module may include a heat sink upon which the plurality of solid state light sources are mounted, and the heat sink may include a hole at its center, coaxial with the longitudinal axis of the module, that receives a narrow end of the funnel element. In another further related embodiment, the lens may be shaped as a cone having a narrow end at the base of the module and a wide end at the top of the module.
In another related embodiment, the lens may fill essentially all the volume between the phosphor surface and the lateral edge of the module, and the excitation light and the phosphor light may propagate through the lens material when inside the module, and the excitation light may reflect off the lateral edge of the module through total internal reflection. In a further related embodiment, the phosphor surface may be an inner surface of the lens. In a further related embodiment, the base of the module may include a heat sink upon which the plurality of solid state light sources is mounted.
In yet another related embodiment, the phosphor surface may receive a portion of the excitation light directly from the plurality of solid state light sources and may receive the remainder of the excitation light from the reflection from the lens. In still another related embodiment, the top of the module may be opaque and may include a reflector to reflect unabsorbed excitation light back toward the phosphor surface.
In yet still another related embodiment, each solid state light source in the plurality of solid state light sources may include a hemispherical lens directly above a respective chip. In still yet another embodiment, the phosphor surface and the lens may be rotationally symmetric about the longitudinal axis of the module. In yet another related embodiment, at least one excitation wavelength may be between 380 nm and 500 nm.
In another embodiment, there is provided a light-producing module. The light-producing module includes: a plurality of solid state light sources arranged in a generally horizontal plane, the plurality of solid state light sources emitting blue light generally upwards with an angular distribution centered around a vertical longitudinal axis of the module; a funnel-shaped phosphor surface having a phosphor for absorbing the blue light and emitting phosphor light having a longer wavelength than the emitted blue light, the funnel-shaped phosphor surface having a generally cylindrical portion centered on the longitudinal axis of the module and extending upward from a central portion of the plurality of solid state light sources, the funnel-shaped phosphor surface flaring radially outward from the longitudinal axis above the generally cylindrical portion; and a generally conical element laterally surrounding the plurality of solid state light sources and extending from the generally horizontal plane of the plurality of solid state light sources to a peripheral edge of the funnel-shaped phosphor surface, the conical element reflecting the blue light upwards from the plurality of solid state light sources to the funnel-shaped phosphor surface, the conical element transmitting the phosphor light from the funnel-shaped phosphor surface.
In a related embodiment, at the generally horizontal plane of the plurality of solid state light sources, the plurality of solid state light sources may be radially disposed between an outer edge of the generally cylindrical portion of the funnel-shaped phosphor surface and an inner edge of the generally conical element. In another related embodiment, the funnel-shaped phosphor surface may asymptotically approach horizontal with increasing radial distance away from the longitudinal axis and with increasing longitudinal distance away from the plurality of solid state light sources. In still another related embodiment, a radial cross-section of the funnel-shaped phosphor surface may have non-convex concavity throughout. In yet another related embodiment, a radial cross-section of the generally conical element may be generally flat. In still yet another related embodiment, the funnel-shaped phosphor surface may emit phosphor light having an angular distribution centered about a local surface normal.
In another embodiment, there is provided a method of producing generally lateral and downward-propagating illumination. The method includes: emitting blue light generally upward, the blue light having an angular distribution centered about a vertical axis; surrounding the vertical axis with a cone-shaped lens that reflects upward any blue light that strikes the outside of the cone, the cone widening in the upward direction; receiving and absorbing the blue light at a funnel-shaped phosphor surface, the funnel widening in the upward direction; emitting phosphor light from the funnel-shaped phosphor surface, the phosphor light being emitted generally laterally and downward; and transmitting the phosphor light through the outside of the cone-shaped lens.
The foregoing and other objects, features and advantages disclosed herein will be apparent from the following description of particular embodiments disclosed herein, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles disclosed herein.
As used herein, the terms “up”, “down”, “vertical”, “lateral”, “horizontal” and the like are for convenience. Such terms are useful when describing a particular light output, and are intended to describe the orientations of particular features on a light module when used as intended. For instance, for an overhead light in an outdoor parking lot, the light module may be mounted above the observer, and may desirably have an output pattern that directs most or all of its light downward and laterally, toward the pavement, with little or none directed upward, toward the sky. For this example, it is instructive to describe the orientations of particular features on the module with respect to their orientations during typical use. A “top” of the module may face upward during use, a “bottom” or “base” may face downward during use. It is understood that such labels do not imply that a particular side of the module inherently and always faces upward or downward, only that during typical use, a so-called “top” side faces upward, a “bottom” side faces downward, and so forth. In actual use, a module may be placed in any desired orientation.
The module 1 includes a plurality of solid state light sources, such as but not limited to light emitting diodes (LEDs) 3, typically mounted on or near a top surface of the base 2. The LEDs 3 may be arranged in a suitable pattern, such as but not limited to rectangular, square, or rotationally symmetric around the longitudinal axis A of the module 1. The LEDs 3 may be arranged in a single plane, in multiple planes, or at different locations along the longitudinal axis. The LEDs 3 may lie generally perpendicular to the longitudinal axis A, so that their surface normals are parallel to the longitudinal axis A. In general, LEDs 3 have a directional output, so that the most light is emitted from the LEDs 3 perpendicular to the face of the LEDs 3. At angles farther away from the surface normal, the light output decreases, so that parallel to the LEDs 3, the light output is essentially zero. In many cases, the angular light output of the bare LEDs 3 may follow a Lambertian distribution. In some cases, the LEDs 3 may have a collimating lens placed above them, which may narrow the angular spread of the light therefrom. Each LED 3 may have its own collimating lens, or there may be one collimating lens for several LEDs 3. In some cases, the collimating lenses are hemispherical or are portions of a sphere.
The LEDs 3 may all have the same output wavelength, or may optionally use different wavelengths for at least two of the LEDs 3. In some embodiments, at least one of the LEDs 3 may have a wavelength in the blue portion of the visible light spectrum, in the range of 450 nm to 475 nm, or in the violet portion of the visible light spectrum, in the range of 380 nm to 450 nm. Emitted wavelengths shorter than 380 nm may also be used, but such short wavelengths are considered to be in the ultraviolet portion of the spectrum, where transmission through common glass may be difficult or impossible. For the purposes of this document, the term “blue” may be used to refer to the wavelength ranges of 450-475 nm, 450-500 nm, 400-475 nm, 400-500 nm, 400-475 nm, 380-475 nm, 380-500 nm, less than 450 nm, less than 475 nm, and/or less than 500 nm.
In general, the spectral output of a light emitting diode has a distribution, usually described by center wavelength and a bandwidth. The bandwidth is often given as a full-width-at-half-maximum (FWHM) of output power. Typical FWHM bandwidths for common LEDs are in the ranges of 15-40 nm, 15-35 nm, 15-30 nm, 15-25 nm, 15-20 nm, 20-40 nm, 20-35 nm, 20-30 nm, 20-25 nm, 25-40 nm, 25-35 nm, 25-30 nm, and/or 24-27 nm.
In typical use, the blue LEDs 3 produce light in the blue portion of the spectrum, referred to in this document as “excitation light” 11. The excitation light 11 is directed onto a phosphor that absorbs the excitation light 11, in the blue portion of the spectrum, and emits light with a longer wavelength, which is referred to in this document as “phosphor light” 13 and 16. The spectral properties of the phosphor light are strongly dependent on the particular phosphor used, but common phosphors emit light with a relatively large bandwidth over the remainder of the visible spectrum, typically from 475-750 nm. In many cases, the phosphor composition may be adjusted so that the phosphor light 13 and 16, optionally combined with the excitation light 11, produces illumination that is aesthetically pleasing to human eyesight.
The module 1 may include a lens 4 that surrounds the longitudinal axis A of the module 1 and defines a lateral edge of the module 1. Such a lens 4 encloses the module 1 for protection, and transmits the output light out of the module 1. In the specific example of
In some embodiments, it is the high angle of incidence of the excitation light 15 is what leads to high reflectivity, rather than any wavelength-dependent properties. In general, a bare air/glass or air/plastic interface shows fairly high power reflectivity at high angles of incidence, with little dependence on wavelength. For incidence from air, incident angles higher than the Brewster's angle tend to show this fairly high reflectivity. For incidence from air, the Brewster's angle is (tan−1 n), where n is the refractive index of the glass or plastic. For incidence from glass or plastic, incident angles higher than the Brewster's angle (tan−1 [1/n]) show this fairly high reflectivity, but angles higher than the critical angle (sin−1 [1/n]) show 100% or nearly 100% power reflectivity due to total internal reflection at the interface. Note that the module 1 may be filled with any suitable gas, such as air or nitrogen, or argon; the critical and Brewster's angles do not change significantly. The module may be sealed, or may have one or more vents. As such, the lens 4 tends to reflect the excitation light 15 at relatively high angles of incidence, while transmitting the phosphor light 14, 17 at relatively low angles of incidence.
The phosphor itself may be disposed on a phosphor surface 5. The phosphor surface 5 may be shaped like a funnel, with a wide end at or near the top of the module 1 and a narrow end at or near the base 2 of the module 1. In some embodiments, the phosphor surface 5 may be on the “outside” or “underside” of the funnel shape. In other embodiments, the funnel shape may be solid or a hollow shell with phosphor particles embedded in the funnel shape. For such embodiments, the phosphor may be embedded in a generally transparent plastic or ceramic material, and then molded to the desired funnel shape. For the purposes of this application, the term “phosphor surface” is intended to mean not only phosphor particles on an external or internal surface, but phosphor particles distributed within a volume. In general, the volume may be relatively thin, such as a shell that forms the funnel surface, or may be relatively thick, such as a solid element with a funnel-shaped downward-facing surface.
The LEDs 3 may be outside the radius of the narrow end of the funnel. The lens 4 may extend from the base 2, where the LEDs 3 may be inside the radius of the narrow end of the lens 4, toward the top of the module 1, where the lens 4 may approach or meet the wide end of the funnel-shaped phosphor surface 5. The phosphor surface 5 may receive and absorb excitation light 12 directly from the LEDs 3, then emit phosphor light 13 that exits 14 the module 1 through the lens 4. Similarly, the phosphor surface 5 may receive and absorb excitation light 15 that reflects off the lens 4, then emit phosphor light 16 that exits 17 the module 1 through the lens 4.
In all such embodiments, the angular profile of the emitted phosphor light is centered about a local surface normal of the phosphor surface 5, the location on the phosphor surface 5 corresponding to the location at which the excitation light is absorbed. For the specific design of
More specific options for the phosphor surface 5 are shown in
In some embodiments, not all of the excitation light 11, 12, 15 is absorbed by the phosphor surface 5, so a reflector 6 is located above the phosphor surface 5 to reflect any transmitted excitation light 11, 12, 15 back downward toward the phosphor surface 5 for potential absorption. The shape of the reflector 6 may be used to further tailor the output profile of the module 1. In the specific embodiment shown in
Note that in
In
Note that the shapes of the phosphor surface 5 and the lens 4 in
In contrast with
In some embodiments, such as shown in
As with the shape of the phosphor surface 5, the shape of the lens 4 (or, in the case of a solid lens, like in
Unless otherwise stated, use of the word “substantially” may be construed to include a precise relationship, condition, arrangement, orientation, and/or other characteristic, and deviations thereof as understood by one of ordinary skill in the art, to the extent that such deviations do not materially affect the disclosed methods and systems.
Throughout the entirety of the present disclosure, use of the articles “a” and/or “an” and/or “the” to modify a noun may be understood to be used for convenience and to include one, or more than one, of the modified noun, unless otherwise specifically stated. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
Elements, components, modules, and/or parts thereof that are described and/or otherwise portrayed through the figures to communicate with, be associated with, and/or be based on, something else, may be understood to so communicate, be associated with, and or be based on in a direct and/or indirect manner, unless otherwise stipulated herein.
Although the methods and systems have been described relative to a specific embodiment thereof, they are not so limited. Obviously many modifications and variations may become apparent in light of the above teachings. Many additional changes in the details, materials, and arrangement of parts, herein described and illustrated, may be made by those skilled in the art.
