This application claims priority from U.S. provisional patent application serial No. 61/268,230, filed on 10/6/2009, the disclosure of which is incorporated herein by reference.
Drawings
The invention is best understood from the following detailed description when read with the accompanying drawing figures. It is noted that, in accordance with common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures:
FIG. 1 is a diagram of a prior art commercially available LED-based lamp;
FIG. 2 is a cross-sectional view of a solid state light source bulb according to a first embodiment of the invention;
FIG. 3 is a cross-sectional view of a solid state light source bulb according to another embodiment of the invention;
FIG. 4(a) shows a cross-sectional view of a light source and a light collimating lens according to another embodiment of the present invention;
FIG. 4(b) is a cross-sectional view of a light source, a light collimating lens, and a conical light guide according to another embodiment of the present invention;
4(c) -4(d) show cross-sectional views of a light source, a light collimating lens, and a conical light guide with a flat tip, according to other embodiments of the present invention;
FIGS. 5(a) -5(d) show cross-sectional views of a light source, a light collimating lens, and a conical light guide with flat tips with flat surfaces oriented at 0, 30, 45, and 60, respectively, according to further embodiments of the present invention;
FIG. 5(e) is a 90 ° rotated view of the embodiment shown in FIG. 5 (d);
6(a) -6(c) illustrate conical light guides having conical top surfaces (with apex angles of 120, 90, and 60, respectively) according to other embodiments of the present invention;
7(a) -7(b) illustrate a blue Light Emitting Diode (LED) having a tapered light guide with a phosphor coated top surface in "off" and "on" states, respectively, according to one embodiment of the present invention;
FIG. 8(a) shows a 3-dimensional perspective view of one embodiment of the present invention with a white LED package;
FIG. 8(b) shows a 3-dimensional exploded view of the embodiment shown in FIG. 8 (a);
FIG. 9(a) shows a 3-dimensional perspective view of another embodiment of the present invention with an SPE type blue LED package;
FIG. 9(b) shows a 3-dimensional exploded view of the embodiment shown in FIG. 9 (a);
fig. 10(a) shows a 3-dimensional view of a heat sink having 6 fins according to one embodiment of the present invention;
FIG. 10(b) shows a cross-sectional view of the embodiment of the invention shown in FIG. 10 (a);
FIG. 11(a) shows a light source, a heat sink and a parabolic first reflector according to another embodiment of the invention;
FIG. 11(b) shows a 3-dimensional cross-sectional view of the embodiment of the invention shown in FIG. 11 (a);
FIG. 12(a) shows a light source, a heat sink and a conical first reflector according to another embodiment of the invention;
fig. 12(b) shows a 3-dimensional cross-sectional view of the embodiment of the present invention shown in fig. 12 (a).
Detailed Description
Although the invention is illustrated and described herein with reference to specific embodiments, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention.
The inventors have found that the performance of Solid State Light (SSL) emitting devices is adversely affected when a light source, such as a Light Emitting Diode (LED), is placed at or within the lamp base. It has been found that positioning the light source at the lamp base generates a level of heat that is detrimental to the efficiency, light generation and lifetime of the SSL-based lamp. Attempts to overcome these deficiencies have focused on bulb designs that differ from conventional incandescent a-lamps.
In commercially available LED-based products, a heat sink (if present) is typically located between the lamp base and the LED source to facilitate heat dissipation. In most cases, the heat sink is formed integrally with the lamp base. However, arranging the heat sink at or within the lamp base prevents proper thermal management of the LED. This is because a large percentage of the heat is conducted only from behind the LEDs to the lamp base, rather than being dissipated from the LEDs to the environment. For example, fig. 1 shows a commercially available LED-based replacement lamp that uses a heat dissipating element at the lamp base. While the use of a heat sink at the bulb base in this manner may promote heat dissipation, the light beam distributed from the replacement bulb is significantly different from the light distributed from a conventional incandescent bulb.
In addition, alternative lamp designs currently on the market have a significantly different aesthetic and light distribution function than conventional incandescent lamps. For example, due to the location and shape of the heat sink employed in commercially available LED-based products, most of the light in the direction of the heat sink is blocked. This has proven to result in a shadow behind the lamp, which is unusual and not identical to incandescent lamps to be replaced by SSL-based lamps. At a minimum, such variations in light distribution can create problems in appearance. In other cases, differences in light distribution may result from completely unacceptable performance of lighting devices designed for incandescent lamps.
The present invention addresses these problems by positioning the light source at the end of the bulb envelope substantially opposite the incandescent a-lamp base. The light source may be at least one semiconductor light emitting diode, such as a Light Emitting Diode (LED), a Laser Diode (LD), or a resonant cavity LED (rcled). Embodiments of the present invention may use a single SSL source, such as a single LED, or may include multiple SSL sources (i.e., multiple LEDs) as light sources. The light source may be connected to a heat sink, wherein at least a portion of the heat sink is located outside the bulb envelope. The positioning of the light source in the inventive arrangement minimizes the effect of the inherent heat at the lamp base on the light source. Furthermore, the heat sink serves as a heat dissipating element for the light source, so that heat can be drawn away from the light source. The heat sink may also provide mechanical support for the light source. For example, the heat sink may be located outside of the bulb envelope but connected to the internal light source at a notch in the bulb envelope. This connection effectively retains the light source within the bulb envelope and also seals the bulb envelope closed. This design feature of the present invention enables a replacement bulb to have very high luminous efficiency values and produce light levels similar to incandescent lamps, while also extending the life durability of SSL-based lamps.
The use of a down-converting material helps to produce light that is aesthetically similar to that produced by a conventional incandescent a-lamp. It should be understood that the terms "down-conversion" and "down-converted" refer to materials adapted to absorb radiation in one spectral region and emit radiation in another spectral region. As mentioned above, the down-conversion material of the present invention may be composed of one or more wavelength conversion materials adapted to absorb radiation in one spectral region and emit radiation in another spectral region, and the wavelength conversion material may be a down-conversion material or an up-conversion material. As such, embodiments of the present invention may incorporate wavelength converting materials that are down-converting materials, up-converting materials, or both. Accordingly, the term "down-conversion material" is defined as a material that by its composition can absorb radiation in any spectral region and emit it in any spectral region. It should also be understood that the terms "transmitted light" and "reflected light" are used throughout this application. More precisely, however, the terms "forward transmitted light" and "reverse transmitted light", respectively. When light emitted from the light source reaches the down-conversion material, the down-conversion material absorbs the short wavelength light and emits down-converted light. The emitted down-converted light may travel in all directions (known as lambertian emitters), and thus, a portion of the down-converted light travels upward while another portion travels downward. Light traveling upward (or outward) from the down conversion material is the forward transmitting portion of the light, while light traveling downward toward the light source is the reverse transmitting portion.
In some embodiments of the present invention, the problem of low performance of existing replacement bulbs is also solved by employing a non-contact down-conversion concept. In one system employing a non-contact down-conversion concept, short wavelength radiant energy from a light source is emitted toward a down-conversion material located remotely from the light source. At least a portion of the radiant energy hitting the down-converting material is down-converted to longer wavelength radiation and, when the two radiations mix, a white light is obtained that is similar to the light produced by an incandescent a-lamp. The down-converting material may be composed of one or more wavelength converting materials adapted to absorb radiation in one spectral region and emit radiation in another spectral region. The plurality of wavelength converting materials are capable of converting wavelengths emitted from the light source to the same or different spectral regions. In some embodiments of the invention employing white LEDs as the light source, a down-conversion material may not be necessary because the emitted light is already substantially similar to that produced by an incandescent lamp. In other embodiments employing white LEDs, specific down conversion materials, such as "red" phosphors, may be selected to enhance the color rendering properties of the white LED. For example, such a configuration would enable the use of a normal white LED with medium quality color rendering properties to obtain a white light output from the LED lamp with better or higher color rendering properties.
A reflector may be used to receive and reflect light emitted by the light source and down-converted by the down-conversion material (i.e., forward transmitted light). The reflector may take any geometric shape such as spherical, parabolic, conical, and elliptical, and may comprise various reflective surfaces known in the art. For example, the reflector may be aluminum, plastic with an evaporated aluminum reflective layer, or any other kind of reflective surface. The reflector is positioned between the down conversion material and the lamp base and may be spaced apart from or adjacent to the down conversion material. In at least one embodiment of the present invention, the down-conversion material is applied to and contained on the reflector using conventional techniques known in the art. By trapping both the forward and reverse transmitted portions of the emitted and down-converted light, system efficiency can be improved. Similarly, the position of the down conversion material and the reflector can be adjusted to ensure that light from the light source strikes the down conversion material uniformly to produce uniform white light and allow more light to exit the device. At the same time, positioning the down conversion material remote from the light source prevents light from being fed back into the light source. As a result, heat at the light source is further minimized and leads to improved bulb life durability.
Optionally, a second reflector may be employed to direct light emitted from the light source. Suitable secondary reflectors include, for example, cup reflectors or optical lenses. When a second reflector is employed, the light source may be disposed within the second reflector. When a plurality of SSL sources are employed as light sources, each SSL source may be disposed within a respective second reflector. Alternatively, all SSL sources may be located within one second reflector. The second reflector may take any geometric shape such as spherical, parabolic, and elliptical, and may be constructed of various materials known in the art. For example, when an optical lens is used as the second reflector, the lens may be any light-transmissive material such as glass and plastic. The second reflector is for directing light emitted from the light source and may be configured to direct substantially all of the light emitted from the light source to the down conversion material. In certain embodiments, the second reflector may be a component of the heat sink and formed integrally therewith. For example, the portion of the heat sink connected to the light source may be or have the function of a second reflector. In this configuration, the second reflector collects light emitted laterally by the light source and directs it away from the light source. This design increases optical efficiency.
The light guide can be used to further simulate the aesthetics and performance of a conventional incandescent a-lamp. For example, a first end of the light guide may be connected to a light source and a second end of the light guide may be connected to the down conversion material. These components may be disposed within the bulb envelope to simulate the filament aesthetics of a conventional incandescent a-lamp. Similarly, when the light source is disposed within the second reflector, the light guide can direct light from the light source and the second reflector to the down-conversion material. Furthermore, since the light guide can be designed in a variety of shapes and sizes, it can be manufactured and positioned to guide substantially all of the light emitted from the light source to the down-conversion material, thereby increasing the efficiency of the SSL device.
The solid state light device of the present invention may also include other components known in the art. For example, the SSL device may also include an electronic driver. Most SSL sources are low voltage Direct Current (DC) sources. Therefore, an electronic driver is needed to regulate the voltage and current for SSL-based lamps. Alternatively, there are some Alternating Current (AC) SSL sources, such as the AC-LED sold under the trade name "Acriche" by Seoul Semiconductor, inc. In these cases, the SSL source (e.g., LED or LED array) may be directly connected to the AC power available from the mains. Thus, embodiments of the present invention may optionally include an electronic driver, at least a portion of which is located within the a-lamp base, depending on the type of SSL source employed in the SSL-based lamp. The invention may also include at least one electronic conductor such as a connecting wire. Electronic conductors may be provided within the bulb envelope to connect electrical current between the lamp base and the light source.
Fig. 2 shows a first exemplary embodiment of the invention having a lamp base 12 (e.g., of the same size and shape as a conventional incandescent a-lamp), a light-transmissive bulb envelope 20, a light source 16 for emitting light, a down-conversion material 22, a reflector 24, and a heat sink 18. The lamp base 12 is a standard base identical to that found in existing incandescent lamps. The bulb envelope 20 may be made of a variety of light-transmissive materials, such as plastic or glass. As shown, a first portion of the bulb envelope 20 is coupled to the lamp base 12, and at least a portion of the light source 16 is disposed within the bulb envelope 20 at an end substantially opposite the lamp base 12. A down conversion material 22 is disposed within the bulb envelope 20. A reflector 24 is also disposed within the bulb envelope 20 and between the down conversion material 22 and the lamp base 12.
The heat sink 18 is shown at the bottom of the bulb envelope 20 and at an end substantially opposite the lamp base 12. At least a portion of the heat sink 18 is external to the bulb envelope 20. The heat sink may comprise a series of metal fins (shown as metal fins 18a in fig. 8a and 8 b). Alternatively or additionally, the heat sink may include a mesh extending from the heat sink 18 and surrounding at least a portion of the outer surface of the bulb envelope 20 between the light source 16 and the bottom of the lamp base 12. Heat sink 18 may be made of a variety of heat dissipating materials known in the art, such as aluminum or copper. The heat sink may be colored, such as white, to enhance or change the heat dissipation capability of the material. At least a portion of the heat sink 18 is external to the bulb envelope 20, but the heat sink 18 is connected to the internal light source 16. This may be accomplished, for example, at a notch at an end of the interior of the bulb envelope 20 substantially opposite the lamp base 12. This connection effectively retains the light source 16 substantially within the bulb envelope 20 and also seals the bulb envelope 20 closed. After assembly, the interior of the bulb envelope 20 may be a vacuum or may be filled with an inert gas such as argon or krypton.
Fig. 2 shows an electronic driver 30 connected to the light source 16 via electrical conductors 32. As described above, an electronic driver 30 is optionally included to regulate voltage and current for SSL-based lamps using a DC SSL source. Alternatively, when an AC SSL source is selected, the electronic driver 30 is not required. Accordingly, embodiments of the present invention may optionally include an electronic driver 30, at least a portion of which is located within the lamp base 12, depending on the type of SSL source employed in the SSL-based lamp. At least one electronic conductor 32, such as a bond wire, may also be employed in the embodiment of the invention shown in fig. 2. An electrical conductor 32 may be provided within the bulb envelope to connect current between the input of the lamp base 12 and the light source 16 through the electrical conductor 32 as desired.
The light source 16 may be disposed within a second reflector 26, which second reflector 26 may be a cup-shaped reflector having an open top. The light source may comprise a plurality of SSL sources, for example a plurality of LEDs, each located within its own second reflector 26. The second reflector 26 concentrates the light emitted from the light source 16 up toward the down conversion layer 22 (which may be a phosphor) and the reflector 24. A lens may be used as the second reflector 26 in place of or in combination with the cup-shaped reflector. The reflector 24 and the second reflector 26 may be aluminum, plastic with an evaporated aluminum reflective layer, or any other type of highly reflective surface. By directing light emitted from the light source 16 toward the down-conversion material 22, the second reflector 26 minimizes the likelihood that light will exit the side of the bulb envelope 20 and be transmitted from the light source 16 to both the down-conversion material 22 and the reflector 24. In the illustrated embodiment, reference numeral 34 denotes a light beam, rather than a physical element, and is not a claimed component of the invention.
In the exemplary embodiment, the down conversion material 22 is positioned closer to the lamp base 12 than the light source 16, and the reflector 24 is adjacent to the down conversion material 22. In an alternative embodiment, the down conversion material 22 may be positioned, for example, across the middle of the bulb at location D, and the reflector 24 may be positioned away from the down conversion material 22. In such embodiments, some of the light reflected from the reflector 24 may escape through the sides of the bulb envelope 20 between the reflector 24 and the down conversion material 22. The down conversion material 22 may also be at a location above the center location D of the bulb envelope 20 (i.e., further away from the lamp base). When light from the light source 16 hits the down conversion material 22 and the reflector 24, some of the light is reflected back (i.e., back transmitted) from the down conversion material and exits the sides of the bulb envelope 20. All light that passes through the down conversion material 22 (i.e., that is forward transmitted) is reflected back by the reflector 24 and exits from the sides of the bulb envelope 20. Although the down conversion material 22 and reflector 24 are shown across the entire width of the bulb envelope 20, these components may be less than the entire width. The position of the down conversion material 22 and reflector 24 within the bulb envelope 20, as well as the size and shape of these components, are adjusted to achieve the desired SSL lamp-based performance efficiency, as will be appreciated by those of ordinary skill in the art.
In exemplary or alternative embodiments, the down conversion material may include one or more phosphors. For example, the down-conversion material may include one or more of: cerium-doped yttrium aluminum garnet (YAG: Ce), europium-doped strontium sulfide (SrS: Eu), europium-doped YAG: Ce phosphor, YAG: Ce phosphor + cadmium selenide, or other types of quantum dots produced from other materials, including lead (Pb) and silicon (Si); and other phosphors known in the art. It will be understood that other embodiments of the present invention may include embedded phosphor layers or non-embedded phosphor layers. Moreover, the phosphor layer need not have a uniform thickness, but rather, it can have different thicknesses, or different phosphors can be mixed to produce a more uniform color output. The down-conversion material may similarly include other phosphors, quantum dots, quantum dot crystals, quantum dot nanocrystals, or other down-conversion materials known in the art. The down-converting material may be a wavelength converting crystal rather than a powder material mixed with a binding medium. As known to those of ordinary skill in the art, the down conversion material layer may include additional scattering particles such as microspheres to improve mixing of light of different wavelengths. In an alternative embodiment, the wavelength converting material layer may be composed of a plurality of continuous or discrete sublayers, each sublayer containing similar or different wavelength converting materials. The down-converting material or individual wavelength converting layers may be formed by any suitable technique known in the art, such as mounting, coating, deposition, screen printing or screen printing.
Fig. 3 shows another embodiment of the invention having a lamp base 12, a light-transmissive bulb envelope 20, a light source 16 for emitting light, a down conversion material 22, a reflector 24, and a heat sink 18. In addition, this embodiment also includes a light guide 28. A first end of light guide 28 is connected to light source 16 and a second end of light guide 28 is connected to down conversion material 22, all of which are substantially located within bulb envelope 20. This embodiment shows the light source 16 disposed within the second reflector 26, also substantially within the bulb envelope 20. A cup-shaped reflector is shown in fig. 3, but as before, an optical lens may be used instead of or in combination with the cup-shaped reflector as the second reflector. Accordingly, the light guide 28 guides light from the light source 16 and the second reflector 26 to the down-conversion material 22. Alternatively, when a second reflector is not employed, light guide 28 may be connected to light source 16 and direct light directly from light source 16. In the embodiment shown in fig. 3, the down conversion material 22 is a small cylinder of wavelength conversion material rather than a layer of material. The down conversion material 22 may be located at a central portion of the bulb, as shown in fig. 3, or at another location to achieve performance and aesthetic goals for the SSL-based lamp. These components may be disposed within the bulb envelope 20 to simulate the filament aesthetics of a conventional incandescent a-lamp. For example, a point source similar to a standard tungsten filament point source is achieved by positioning a cylindrical down-conversion material 22 in the center of the bulb, i.e., on top of the tapered light guide 28. Fig. 3 also shows the reflector 24 spatially remote from the down conversion material 22. In this embodiment, since the down conversion material is too small, not much of the light reflected from the reflector 24 will strike the down conversion material 22. However, the light guide 28 serves to ensure that substantially all of the light emitted from the light source 16 is directed toward the down conversion material 22 where it can be down converted and exit the bulb envelope 20 as white light.
Fig. 4(a) -4(e) illustrate various embodiments of the present invention employing a second reflector. The figures show the second reflector as an optical lens, but the second reflector may also be a cup-shaped reflector. The SSL light source, such as an LED, can be placed inside the optical lens, as shown in fig. 4 (a). Fig. 4(b) -4(e) may also include a light guide. The light source, the second reflector and the light guide are substantially located within the bulb envelope. The lens and the light guide may be manufactured as a single component or may comprise two separate components. The light guide may take a variety of shapes and sizes. For example, the light guide may be a tapered cylinder, as shown in fig. 4(b) -4(e), or it may be a right cylinder. The top of the light guide may be pointed (as shown in fig. 4 (b)) or flat (as shown in fig. 4(c) -4 (e)). Fig. 4(c) -4(e) also show that the light guides can have different lengths and sizes. For example, fig. 4(c) -4(e) show light guides with lengths of 40mm, 35mm and 30mm, respectively.
The top of the light guide may also be chamfered at different degrees. For example, fig. 5(a) -5(d) show tapered light guides with flat tops having flat surface orientations of 0 °, 30 °, 45 °, and 60 °, respectively. Fig. 5(e) is a 90 ° rotated view of the embodiment shown in fig. 5(d) to further illustrate the light guide design. In addition, the top of the light guide may be spherical (sphere), hemispherical, conical, as shown in fig. 6(a) -6 (c). Fig. 6(a) -6(c) show tapered light guides with conical top surfaces having apex angles of 120 °, 90 °, and 60 °, respectively. A non-contact down-conversion material is placed at these end faces on top of the light guide. 7(a) -7(b) illustrate a blue Light Emitting Diode (LED) having a tapered light guide with a phosphor coated top surface, according to one embodiment of the present invention. Fig. 7(a) shows the SSL-based lamp in the "off" state, while fig. 7(b) shows the SSL-based lamp in the "on" state.
Fig. 8(a) shows a 3-dimensional perspective view of one embodiment of the present invention including a white LED package as a light source. Fig. 8(b) shows a 3-dimensional exploded view of the embodiment shown in fig. 8 (a). These figures show the heat sink 18 as having 6 heat fins 18a outside the bulb envelope 20. Alternative embodiments of the present invention may use more or fewer cooling fins. Alternatively or additionally, the heat sink 18 may include a mesh extending from the heat sink 18 and surrounding at least a portion of the outer surface of the bulb envelope 20 between the light source 16 and the bottom of the lamp base 12. The heat sink 18, fins 18a and mesh may be made of a variety of heat dissipating materials known in the art, such as aluminum or copper. Fig. 8(b) also shows a notch in the bulb envelope 20 for inserting the second reflector 26 and the light source 16 into the bulb envelope. The heat sink 18 is substantially external to the bulb envelope 20 and is coupled to the light source 16 at a notch in the bulb envelope.
Fig. 9(a) shows a 3-dimensional perspective view of another embodiment of the present invention comprising an SPE type blue LED package as a light source. The SPE type LED package uses Scattered Photon Extraction (SPE) and, in at least one embodiment, includes an LED light source 16, a second reflector 26, a light guide 28, and a down conversion material 22 coupled together in a bulb envelope 20. Fig. 9(b) shows a 3-dimensional exploded view of the embodiment shown in fig. 9 (a). As shown in fig. 3, the embodiment of the invention shown in fig. 9(a) and 9(b) includes a small cylindrical down-conversion material 22 located on top of a tapered light guide 28. The light guide 28 is connected to the second reflector 26, in which the light source 26 is arranged. The second reflector 26 and the light guide 28 serve to direct substantially all of the light emitted from the light source 16 into the down-conversion material 22. These figures also show that the heat sink 18 has 6 heat dissipating fins 18a outside the bulb envelope 20. Other embodiments of the invention may include more or fewer cooling fins. Alternatively or additionally, the heat sink 18 may include a mesh extending from the heat sink 18 and surrounding at least a portion of the outer surface of the bulb envelope 20 between the light source 16 and the bottom of the lamp base 12. The heat sink 18 is substantially external to the bulb envelope 20 and is coupled to the light source 16 at a notch in the bulb envelope.
In at least one embodiment of the invention, the second reflector may be a component of, or integral with, the heat sink. Fig. 10(a) shows a 3-dimensional view of the light emitting apparatus according to the embodiment of the present invention, and fig. 10(b) shows a sectional view thereof. In other words, the portion of the heat sink connected to the light source may be or have the function of a second reflector. In this configuration, the second reflector collects at least a portion of the light emitted from the light source from the side and directs it away from the light source to increase optical efficiency. As shown in fig. 10(a) -10(b), the light source 16 is disposed within the heat sink 18 and/or is coupled to the heat sink 18. The portion of the heat sink 18 that is connected to the light source 16 acts as a second reflector to collect and direct light emitted from the side of the light source away (depicted as dashed line 34 in fig. 10 (b)).
Fig. 11(a) -11(b) and 12(a) -12(b) show other embodiments of the invention that include a light source, a heat sink, and a first reflector. Fig. 11(a) -11(b) show embodiments comprising parabolic first reflectors, and fig. 12(a) -12(b) show embodiments comprising conical first reflectors. As described above, the first reflector may take any geometric shape such as spherical, parabolic, conical, and elliptical, and may include various reflective surfaces known in the art. For example, the reflector may be aluminum, plastic with an evaporated aluminum reflective layer, or any other kind of reflective surface. Additionally or alternatively, the reflector may be coated or treated to achieve a particular light distribution or aesthetic effect, or it may even transmit a small portion of the light to prevent the reflector from forming a sharp shadow. The reflector is located between the light source and the lamp base and, when a down-converting material is employed, may be spaced apart from or adjacent to the down-converting material. In at least one embodiment of the present invention, the down conversion material is applied to and contained on the side of the reflector facing the light source using conventional techniques known in the art. Reflectors are used, for example, to enhance the optical efficiency of SSL-based lamps.
The heat entering the lamp base from the LED light source and the electronic driver limits the total capacity of the LEDs that can be reliably used and thus the amount of light that can be produced. In currently available products employing LEDs and optional heat sinks located at or within the lamp base, the amount of light is typically limited to the equivalent of a 25-40w incandescent a-lamp. Embodiments of the present invention place the LED source and heat sink at the apex of the light bulb to dissipate more of the heat generated by the LED to the environment. This configuration enables a greater amount of light to be produced (e.g., the equivalent of a 60w incandescent a-lamp) while ensuring that the proper LED and electronic driver operating temperatures are maintained. This configuration may be even more beneficial for applications using LEDs in open lighting devices when compared to the benefits achieved in fully enclosed lighting devices.
As previously mentioned, the radiant energy hitting the down conversion material will be converted to higher wavelength radiation and when mixed it provides white light similar to that produced by an incandescent a-lamp. The spectrum of the final light output depends on the down-conversion material. The total light extraction depends on the amount of light reaching the down-conversion layer, the thickness of the down-conversion layer and the material and design of the reflector. The shape and size of the light guide may be any design that achieves the performance and aesthetic objectives of the SSL-based lamp. The following embodiments and tables detail a number of exemplary shapes for the light guide, and the effect that each of these shapes may have on the efficiency and light radiation of the SSL-based lamp.
Examples
In at least one embodiment of the present invention, an LED package with Scattered Photon Extraction (SPE) is implemented. Unlike typical conventional white LED packages where the down-conversion phosphor is spread around the light source or chip, in the SPE package of the present invention, the phosphor layer is removed from the chip, leaving a transparent medium between the chip and the phosphor. The effective geometry for such packages can be determined via ray trace analysis. It is worth mentioning that SPE packages require different phosphor densities to produce a white LED package having similar chromaticity coordinates as conventional white LED packages. This difference is a result of SPE packages that mix transmitted and backreflected light with different spectra, whereas conventional packages use primarily transmitted light.
Ray tracing analysis was performed to evaluate the feasibility of the light guide concept. In addition, laboratory evaluations were conducted to investigate the total light output and illumination efficiency. Computer simulations were performed to determine the light coupled into the tapered light guide, the output white light, and the overall efficiency of the system. The base model consists of a blue LED with a non-contact phosphor and a Total Internal Reflection (TIR) lens as a secondary reflector. The blue LED has a lambertian intensity distribution and a spectral peak wavelength of 451 nm. A TIR lens is mounted on top of the LED to collimate the light from the blue LED to the top surface of the TIR lens (as shown in fig. 4 (a)). The tapered light guide is then bonded atop the TIR lens.
Simulation test
To determine the operational and preferred geometry of the tapered light guide, a conical tapered light guide of 50mm height was first tested. The bottom surface of the tapered light guide has the same diameter-width as the TIR lens top surface. To couple more light to the top surface of the tapered light guide and minimize the top surface area, a range of light guide heights were simulated (as shown in fig. 4(c) -4 (e)), and the optimal height of the light guide was selected to be 35mm, as shown in table 1. If a tapered light guide with a lower height is used, there is a trade-off between increased light received at the top surface and an increased area of focus at the top surface. The smaller area on the top surface means that less phosphor is used and a better focused beam can be produced. In view of this trade-off, a 35mm tall tapered light guide was chosen with a fairly small top surface area and a high proportion of light transmitted forward from the top surface.
Table 1: radiated power from top surface of tapered light guide having different heights
After the geometry of the tapered light guide was determined, the flat circular top surface of the tapered light guide was coated with a 0.24mm thick layer of down-conversion phosphor. Various orientations of the flat top surface of the tapered light guide were simulated as shown in fig. 5(a) to 5 (e). Table 2 shows the light output and chromaticity from each tapered light guide white LED package. Simulations show that the light output and thus the system efficiency is maximized at similar chromaticity values when the top surface is oriented at 60 degrees. However, with the use of larger amounts of phosphor, high light output and system efficiency are compromised. One drawback of a flat top surface tapered light guide is the non-uniformity of the spatial color distribution, which is caused by the asymmetric spatial distribution of the phosphor coating.
Table 2: radiant power and chromaticity for tapered light guide white LED packages with multiple top surface orientations
To overcome the potential drawbacks of flat top surface tapered light guides, another type of tapered light guide with a tapered top surface was simulated. The conical top surface is like the pencil tip shown in fig. 6(a) to 6 (c). Three different apex angles of the conical top surface were simulated, each having a uniform phosphor coating 0.24mm thick covering the conical top surface. As shown in table 3, the tapered light guide with a 60 degree conical top surface produced the highest radiant power light output with matching chromaticity values. This is associated with the highest system efficiency. However, again, high output power and system efficiency results are found at the expense of the larger amount of phosphor required. It was confirmed that a tapered light guide with a conical top surface provided better spatial color uniformity than a tapered light guide with a flat top surface.
Table 3: radiant power and chromaticity for tapered light guides with conical top surfaces of various apex angles
Laboratory studies
A lens is used with a high power blue LED to couple light into a cylindrical optical light guide. At 8mg/cm2Area density of (c) YAG: a thin layer of Ce phosphor is coated on top of the lens. Experimental studies were performed using a blue LED driven at 350 mA. The chromaticity, light output and system efficiency were measured in a calibrated integrating sphere. As shown in table 4, the efficiency of this non-contact phosphor white LED package was 11% lower compared to the Scattered Photon Extraction (SPE) package. However, SPE packages have previously demonstrated 61% higher efficiency than conventional phosphor converted white LED packages. Accordingly, the efficiency of this new tapered light guide white LED package is about 50% higher than conventional phosphor converted white LED packages. Accordingly, less phosphor is used in this new tapered light guide white LED package than in conventional systems, and a more focused beam of light is produced from the new white LED package. A more focused beam and less phosphor usage is desirable for LED a lamps for application purposes as well as cost considerations.
Table 4: light output, system efficiency and chromaticity for tapered white LED packages compared to previous SPE packages
It will be understood that the geometry of the SSL-based lamp is not limited to the specific shapes shown in the figures, shown above, or proposed in the embodiments. Alternative shapes may be used to achieve a particular performance or aesthetic, while addressing other design issues, such as color of light and bulb life. Although the present invention has been described with reference to exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed to include other variants and embodiments of the invention which may be made by those skilled in the art without departing from the true spirit and scope of the invention.