Patent Application
20090251882
1. Field of the Invention
The present invention relates generally to illumination devices.
2. Description of the Related Art
Conventional illumination devices include incandescent lamps which are filled with an inert gas to reduce evaporation of a glass-enclosed filament. Electrical current flows through various arrangements of electrical contacts (e.g., an Edison screw and a bayonet base) to heat the filament to an extremely high temperature (e.g., 2000 to 3300 Kelvin). In a halogen version, the glass envelope is filled with a halogen gas. Halogen lamps can thus operate at a higher filament temperature to thereby provide a higher luminous efficiency.
In contrast, current flow through a fluorescent lamp excites mercury vapor in argon or neon gas which generates a plasma that produces short-wave ultraviolet light. This light causes a phosphor coating on the lamp's inner surface to fluoresce and produce visible light. A ballast is included to regulate the flow of power through the lamp. Fluorescent lamps are often housed in a long, slender glass tube (generally positioned between straight bipin bases) but in compact fluorescent lamps (CFLs), the tube is formed in a spiral arrangement which is carried on an Edison screw so that the lamp can replace an incandescent light bulb.
Although the purchase price of incandescent lamps is low and their color rendering index is quite high, their luminous efficacy is poor and their life span is limited to something on the order of 1,000 hours. The life span of fluorescent lamps is significantly higher (e.g., on the order of 10,000 hours) and their luminous efficacy is better but their color rendering index does not match that of incandescent lamps.
The present invention is generally directed to light-emitting diode illumination devices. The drawings and the following description provide an enabling disclosure and the appended claims particularly point out and distinctly claim disclosed subject matter and equivalents thereof.
In particular, the illumination device embodiment 20 of
The base 23 can take a variety of forms that are suitable for installation into various conventional lighting fixtures. In one embodiment, therefore, the base is configured as an Edison screw. Edison screws form a system of light bulb connectors in which a designation Exx refers to the base diameter in millimeters. For example an E26 Edison screw has a base diameter of 26 millimeters and is widely available for installation into conventional household lamps in the United States. Electrical contact is made through a threaded outer surface 27 and an inner contact 28. Other base embodiments may be formed in accordance with other typical lighting bases (e.g., bayonet mounts and straight bipin bases).
A primary light source is provided to generate primary emitted light which excites the generation of secondary emitted light from a secondary light source. In a device embodiment, the secondary light source is the phosphor 24 and the primary light source is formed with a plurality of spaced light-emitting diodes (LEDs) 36. Although wavelengths of the primary emitted light and wavelengths of the secondary emitted light of the excitation source 24 can be anywhere in the electromagnetic spectrum, they are in the visible spectrum (e.g., between 400 and 700 nanometers) in at least some illumination device embodiments.
The phosphor 24 is formed of various phosphorescent or luminescent materials that emit light at emission wavelengths (e.g., wavelengths above 500 nanometers (nm)) when excited by light at excitation wavelengths (e.g., wavelengths below 480 nm). Typical phosphors are combinations of various elements (e.g., cerium, yttrium, aluminum, and garnet) that are generally powdered and bound or suspended in various carriers (e.g., adhesives and solvents). They can be deposited as films or mixed into other materials such as resins and polymers. Exemplary phosphors are provided by various manufacturers such as Intermatix in Fremont, Calif. (e.g., see phosphor data sheets in Intermatix's 2008 Product Catalog) and Molecular Technology headquartered in Berlin, Germany.
In
The redirector 25 is preferably hollow and fabricated from a material (e.g., aluminum or a metallized polymer) which is a good heat conductor. The redirector is positioned so that its outer surface is spaced inwardly from the bulb 22. The redirector is preferably supported by the base 23 which also serves as a portion of a heat path to remove generated heat. Although the redirector 25 can take on other shapes, it has a bulbous shape in the embodiment of
When a redirector embodiment is formed of a metal (e.g., aluminum), each of the redirector portions may be easily formed by a conventional process (e.g., deep drawing or blow molding) prior to joining along the seam 30 with another conventional process (e.g., welding). When a redirector embodiment is formed of a polymer, each of the redirector portions may be formed by a conventional process (e.g., injection molding) prior to joining along the seam 30 with another conventional process (e.g., pressure and/or heating). In another fabrication embodiment, the redirector 25 may be formed as a single piece by using appropriate fabrication techniques (e.g., articulated tooling).
Preferably, the primary and secondary light sources (e.g., at least one LED 36 and at least one phosphor) are spaced apart by a void (i.e., an empty space) and the secondary light source is shaped about the primary light source to permit redirection and excitation processes in the illumination device 20 to be unimpeded. In addition, the redirector's outer surface is preferably configured to enhance its redirective quality. For example, embodiments of the redirector 33 may include a finish (e.g., a nickel plating or a high-gloss white coating) that enhances reflection of light. In other redirector embodiments, the surface of the redirector 33 may be configured in various shapes (e.g., facets 33 indicated in
Although the bulb 22 and redirector 25 can be formed in embodiments that allow the redirector to be received within the bulb, the embodiments shown in
The redirector 24 forms a redirective support for carrying the LEDs 36 whose emitted light can energize the phosphor 24 that is carried by the bulb 22. The LEDs are preferably carried by a substrate 38 which also carries at least one conductor 39 (e.g., a metallic wire) that electrically connects to the electrodes of the LEDs 36. Although the substrate can be formed with various materials, it is formed of a transparent or translucent flexible polymer (e.g., polyethylene or polypropylene) in at least one embodiment. In this embodiment, it easily takes on the shape of the bulbous redirector which supports it. The substrate 38 carries the conductor 39 down into the base 23 where it joins to the base contacts 27 and 28 or joins to electronic elements which are, in turn, joined to the base contacts.
In the device embodiment shown in
In response to excitation by both of the light rays 40 and 42, the phosphor 24 emits excitation light of which a portion 44 travels outward and a portion 45 travels inward to also be redirected from the redirector 25 so that at least some of the portion 45 also continues outward from the bulb 22. Accordingly, light is emitted from the excited phosphorus and the surface of the redirector 25 redirects and enhances the amount of this phosphorus-emitted light which is directed outwardly from the bulb 22.
These emission and excitation processes generate a substantial quantity of light and the redirection processes enhance the amount of this light that is directed outward from the illumination device 20. The light issuing outward from the device comprises a portion which was emitted from the LEDs at an LED wavelength and a portion which was emitted from the excited phosphorus at a phosphorus wavelength. The redirection and excitation processes insure that these portions are mixed and diffused. In a device embodiment, the phosphor 24 is arranged in a pattern (e.g., a checkered or spotted pattern). In another device embodiment, the phosphor is arranged to not have a pattern (e.g., in a continuous film) so that the device's light appears constant (i.e., with an absence of bright spots).
As noted above, the substrate 38 is shaped to space the LEDs 36 over the upper portion of the redirector 25. In the embodiment shown in
In a device embodiment, the LEDs 36 may be blue LEDs which emit light with an emission peak below 480 nm (i.e., the emitted light has a spectrum with a peak below the wavelength of 480 nm). The phosphorus 24 is configured to be excited by this emission peak and emit light with an emission peak that differs from that of the LED light. Exemplary emission peaks of exemplary phosphors are above 500 nm and include the emission peaks of 540, 560, and 585 nm which are associated respectively with green, yellow, and orange light.
In one embodiment, each LED may emit blue light with an emission peak of 455 nm and the phosphorus may be excited to emit yellow light with an emission peak of 550 nm. As shown in
The illumination device 20 is thus configured to facilitate a selection of LED-emitted light and phosphorus-emitted light which may be selected to vary the emitted light's color rendering index (CRI). CRI is a measure of the ability of a light source to accurately reproduce the color of objects lit by the source's emitted light. The best possible rendition of colors is given by a CRI of 100 while the very poorest is given by a CRI of zero.
Another measure of the device's emitted light is given by its color temperature wherein light with a low color temperature on the order of 2800 degrees Kelvin (K) has a red-yellow tone, light with a color temperature on the order of 5000-6000K appears substantially white, and light with a high color temperature above 6000K has a blue tone. The illumination device 20 is thus configured to permit a selection of LED-emitted light and phosphorus-emitted light which may be mixed to realize a desired color temperature. In addition, the structure of the illumination device 20 mixes the LED-emitted light and phosphorus-emitted light so that it is diffused and appears as a uniform color. Without this structure, each LED would appear as a bright spot within a background of lower intensity.
Attention is now directed to
In some illumination structure embodiments, a semiconductor AC-DC voltage converter 50 may be fabricated on a miniature circuit such as an integrated-circuit chip 51 and connected to provide a desired DC voltage to the string of LEDs. In one embodiment, the LED current can be controlled with a semiconductor current mirror 52 which can be incorporated in the integrated-circuit chip 51. Various combinations of resistors, converters and current mirrors may be used to controllably set the voltage across each LED (e.g., in a range of 1.8 to 3.6 volts depending on the LED color) and the current through each LED (e.g., in a range of 15-20 milliamps depending again on the LED color).
In one embodiment, each LED 36 in
In the structure of
As shown in
Studies have shown that the color temperature of light can have significant effects on humans. These effects may be related to changes in the hormone melatonin which is believed to be secreted by the brain and believed to play a role in regulating the body's internal clock. It has been found, for example, that blue light can lower blood pressure and have a calming effect while yellow light has the opposite effects.
Although the phosphors of the illumination device 20 can be selected to adjust the color temperature of the device's light, the color temperature is fixed once this selection has been made and once the emitting wavelength of the LEDs 36 has also been selected. In contrast, the illumination device 80 of
The illumination device 80 includes elements of the device 20 of
To make room for them, the LEDs 86, substrate 88 and conductor 89 are rotated (e.g., by 22.5 degrees) from the LEDs 36, substrate 38 and conductor 39. It is noted that the substrates 38 and 88 can also be combined into a single substrate. In addition, the conductors 38 and 88 are coupled to a switch 90 (e.g., a variable switch or a 3-way switch) adjacent the base 23.
The device 80 thus provides at least one phosphor 24 that is carried on the bulb 22 and also provides a first diode group comprising the LEDs 36 and a second diode group comprising the LEDs 86. In an exemplary device embodiment, the phosphor (or phosphors) 24 is selected to have an emission peak above 500 nm, the LEDs of the first diode group are configured to have first emission peaks located at a first spectral region below 480 nm, and the LEDs of the second diode group are configured to have second emission peaks located at a second spectral region below 480 nm that differs from the first region. With the switch 90, a device user can selectively energize either of the first and second diode groups.
For example, the phosphor can be a mix of green, yellow and red phosphors, the LEDs of the first group can have a first emission peak at 380 nm, and the LEDs of the second group can have a second emission peak at 470 nm. When the phosphors are excited by the LEDs of the first group, their emission peaks will shift relative to their locations when they are excited by the LEDs of the second group. Thus the emission peaks of both the LED-emitted light and the phosphor-emitted light can be selectively altered (e.g., via the integrated-circuit chip 51 of
In other illumination device embodiments, the first and second groups of LEDs can both be commanded on with the currents of each of these groups selectively altered (e.g., via the integrated-circuit chip 51 of
At the left side of the graph 100, the phosphors are being excited by light which contains a greater quantity of light from the 380 nm LEDs than from the 470 nm LEDs. In response, the wavelengths of the phosphor-emitted light tend to increase which lowers the color temperature of the light from the illumination device (e.g., to 2500K). At the right side of the graph 100, the phosphors are being excited by light which contains more light from the 470 nm LEDs than from the 380 nm LEDs. In response, the wavelengths of the phosphor-emitted light tend to decrease which raises the color temperature of the light from the illumination device (e.g., to 7500K). The light issuing from the illumination device can thereby be continuously adjusted from a red-yellow tone at one extreme to a blue tone at the other extreme.
The currents in the first and second groups of LEDs can be controlled with electronic switches (e.g., metal-oxide-semiconductor (MOS) transistors) that replace (or supplement) the mechanical switch 90 shown in
In other device embodiments, a variety of different control circuits can be incorporated (e.g., the integrated-circuit chip 51 of
In contrast to the arrangement of the illumination device 20 of
The lower portion of the redirector effectively acts as a heat path to direct heat away from the LEDs 36 by conducting a portion to the base 23 and radiating another portion outward from the redirector. This heat radiation is enhanced by configuring the lower portion to have a greater radiating area. For example, the lower portion can be configured with heat-radiating protuberances 130.
Electronic circuits 136 may be carried in the lower portion of the redirector 125. For example, a semiconductor AC-DC voltage converter may be fabricated as an integrated-circuit chip and connected to provide a desired DC voltage to the string of LEDs. Another cutout 137 shows that insulation 138 (e.g., a heat insulating silicon layer) may be carried over the inner surface of the redirector 125 to direct heat away from the circuits 136 and direct it, instead, downward to the base 23 or outward through the protuberances (e.g., 132 and 133).
It is important to note that the interior of disclosed illumination device embodiments need not be sealed from the exterior and there need not be a pressure differential between interior and exterior as in conventional illumination devices. This simplifies illumination device structure and reduces the cost of illumination device embodiments. It is further noted that other illumination device embodiments may eliminate the phosphor (24 in
Accordingly, the redirector 25 has been modified to a redirector 145 that is partially within a reconfigured bulb 142 and partially outside of the bulb. A lower portion of the redirector extends upward from a base 23 and terminates in a step 146 that carries the bulb 142. Above this step, an upper portion of the redirector is essentially the same as the redirector 25 of
The illustrated illumination device embodiments (and other embodiments which can be readily envisioned to achieve substantially equivalent results) offer substantial advantages over conventional illumination devices. For example, the average life span of LEDs is an order of magnitude greater than the life span of fluorescent devices and another order of magnitude greater than the life span of incandescent devices. The obtainable CRI of LEDs compares favorably with those of fluorescent and incandescent devices while the luminous efficacy (the fraction of electromagnetic radiation which is useful for lighting) of LEDs is significantly greater.
LEDs are more durable than fluorescent and incandescent devices and when the bulb 22 of
The illumination devices illustrated in
The embodiments of the invention described herein are exemplary and numerous modifications, variations and rearrangements can be readily envisioned to achieve substantially equivalent results, all of which are intended to be embraced within the spirit and scope of the appended claims
