Lighting system of adjustable color temperature

A lighting system capable of adjusting color temperature is provided. The lighting system mainly comprises a light source module and a mixing assembly. The light source module produces red-color, blue-color, and green-color lights so as to control the color temperature of a white light resulted from mixing the color lights. The mixing assembly is located at a side of the light source module and comprises a first, a second, and a third mixing device sequentially arranged along the light transmission path. The function of the first and third mixing devices is for light mixing by causing the lights to undergo multiple internal reflections. The second mixing device directs the lights passing through the first mixing device in a reverse direction (180 degrees) and enters into the third mixing device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to lighting systems and, more particularly, to lighting systems capable of producing high-brightness, high-uniformity white light of the required color temperature.

2. The Prior Arts

Today's lighting systems, which commonly utilize incandescent lamps and halogen lamps, are simple and easy to use. However, they usually require larger input power and their lighting quality often deteriorates after long period of use. As such, new lighting systems for the next generation are continuously developed and proposed. Among them, light-emitting diode (LED) based lighting systems seem to be the most promising one, especially after the white-light LEDs are successfully developed. Under the current technology, however, the white-light LEDs are usually slightly bluish in color, expensive, and have a short operation life. LED-based lighting systems therefore are not commonly adopted yet.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a lighting system capable of producing lights with high brightness, high uniformity, and adjustable color temperature. The lighting system mainly utilizes a light source module whose mix of red, green, and blue lights is adjustable so as to produce a white light with the required color temperature. The white light then passes through a mixing assembly for a uniform mixing and the final output of the lighting system therefore has the required color temperature, a high brightness, and a uniform color.

Another objective of the present invention is to provide a lighting system having a superior mixing effect and a small form factor. The mixing assembly, based on the total reflection theory, has its reflective surfaces made of a material having a high reflection index. The mixing assembly utilizes at least a mixing device to alter the transmission path of the lights (up to 180 degrees) produced by the light source module. The mixing assembly therefore, on one hand, causes the lights to undergo enough number of times of reflection to achieve a uniform mixing and, on the other hand, effectively reduces the overall dimension of the lighting system.

To achieve the foregoing objectives, the present invention mainly comprises a light source module and a mixing assembly. The light source module is composed of multiple red-color, green-color, and blue-color LEDs. By controlling the current injected into these LEDs, lights resulted from different proportions of red, green, and blue colors, and thereby of the required color temperature, are produced. The mixing assembly comprises a first, a second, and a third mixing device sequentially arranged along the light transmission path. The function of the first and third mixing devices is for light mixing by causing the lights to undergo multiple internal reflections. The second mixing device comprises multiple reflective surfaces so that the lights, after passing through the first mixing device, are reversed in direction (180 degrees) and enter into the third mixing device.

The advantages of the present invention can be summarized as follows: (a) this lighting system of adjustable color temperature could be tuned to suit a geographical region's specific preference (for example, more yellowish white lights for Europe and North America, and whiter white lights for Asia); (b) this lighting system, by using LEDs as light source, has lower power consumption and better luminous efficiency; and (c) this lighting system is more convenient to use due to the reduced form factor.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, detailed description along with the accompanied drawings is given to better explain preferred embodiments of the present invention. Please be noted that, in the accompanied drawings, some parts are not drawn to scale or are somewhat exaggerated, so that people skilled in the art can better understand the principles of the present invention.

FIG. 1is a schematic diagram showing a preferred embodiment of the lighting system according to the present invention. As shown inFIG. 1, the present invention comprises a light source module1and a mixing assembly that in turn comprises a first mixing device2, a second mixing device3, and a third mixing device4.

The lights produced by the light source module1are formed by mixing red-color, green-color, and blue-color lights in different proportions. The red-color, green-color, and blue-color lights are from light emitting devices within the light source module1. In the present embodiment, the light emitting devices are red-color, green-color, and blue-color LEDs. By controlling the current injection into these LEDs, the luminous intensity of LEDs of a specific color could be adjusted independently. The proportions of the red-color, green-color, and blue-color lights in the white lights produced by the light source module1, therefore, can be adjusted as well.

FIGS. 3aand3bare schematic diagrams showing two possible arrangements of the LEDs within the light source module of the lighting system according to the present invention. As shown inFIGS. 3aand3b, the light source module1is composed of pre-determined numbers of red LEDs11, blue LEDs12, and green LEDs13, arranged in an evenly distributed and interleaving fashion. The arrangement shown inFIG. 3ais for matching a rectangular incident end of the first mixing device, and the arrangement shown inFIG. 3bis for matching a circular incident end of the first mixing device (more details later). The white lights produced by the light source module1are formed by mixing the red-color, green-color, and blue-color lights emitted from the LEDs11,12,13. The luminous intensity of the white lights is determined by the numbers of these various colored LEDs and their patterns of arrangement. The color temperature of the white lights, on the other hand, is determined by the amounts of current injected into the various colored LEDs.

As shown inFIGS. 1 and 2, the mixing assembly is configured at a side to the light source module1. The lights produced from the light source module1are directed into the mixing assembly and uniformly mixed by multiple reflections inside the mixing assembly. The mixing assembly comprises, sequentially along the lights' transmission path, a first mixing device2, a second mixing device3, and a third mixing device4. The function of the first and third mixing devices2,4is for light mixing, thus, causing the lights to undergo multiple internal reflections. The second mixing device3has an end attached to the first and third mixing devices2,4and alters the lights' transmission path so that the dimensions of the first and third mixing devices2,4can be reduced.

Geometrically, the first and third mixing devices2,4are in the shape of a conoid, such as a cone or a polygonal conoid. For both the first and third mixing devices2,4, the wall of the conoid is inclined at an angle β between 0° and 45°, and a material6having a high reflection index is coated on the wall's external surface. The conoid's two open ends are planar and the cross-section could be in the shape of circle, rectangle, or polygon (the LEDs in the light source module are arranged to match the shape here). An open end22of the first mixing device2and an open end41of the third mixing device4are attached to an end31of the second mixing device3. The connecting ends22and41have identical shapes and areas.

In the present embodiment, the second mixing device3is a triangular prism. The prism has a vertex angle α between 60° and 120°, and the material6having a high reflection index is coated on the prism's external surface. As such, lights emitted out of the first mixing device2through the connecting end22are reflected into the third mixing device4via the connecting end41.

The first, second, and third mixing devices2,3,4could be made of glass, or polymers, such as polycarbonate (PC), polystyrene (PS), and polymethylmethacrylate (PMMA). When using polymers, the mixing devices can be fabricated by injection molding so as to increase the yield and to lower the production cost. The material6could be silver, aluminum, or gold.

With reference toFIG. 2, the dimensions of the relevant parts of the mixing assembly are related as follows:
w12=w11+2×h1×tan β
wherein,w11is the incident end21's aperture of the first mixing device2,w12is the connecting end22's aperture of the first mixing device2, andh1is the height of the first mixing device2; and
w22=w21+2×h2×tan β
wherein,w21is the connecting end41's aperture of the third mixing device4,w22is the emitting end42's aperture of the third mixing device4,h2is the height of the third mixing device4, andw12=w21.

From the foregoing description and dimension definitions of the relevant parts, a light's incident angle into the first mixing device2and the light's emitting angle out of the third mixing device4satisfy the following equations:
sin2(θin)×(w11)2=sin2(θout)×(w22)2,
w22=w11+2×(h1+h2)×tan β
wherein,θinis the incident angle, andθoutis the emitting angle.

In the present embodiment, the first and third mixing devices2,4are for mixing lights uniformly by multiple internal reflections. The principles used behind the first and third mixing devices2,4are identical and, therefore, only the operations of the first mixing device2are explained in the following. In general, reflection is caused by one of two types of mechanism. One is by totally internal reflection and the other one is by a material having a high reflection index. As shown inFIG. 4, the first mixing device2is mainly made of a material having a refraction index n2. Around its wall, the first mixing device2has another medium layer8having a refraction index n1(n2>n1). On the external surface of medium layer8, a material6having a high reflection index is coated. When a light k1shoots on the internal surface5, if k1's incident angle θ1is greater than the total reflection angle sin−1(n1/n2), total reflection would occur. If the incident angle θ1is less than the total reflection angle sin−1(n1/n2), as in the case of light k2, the light k2would be refracted and enter the medium layer8. When the light k2touches the material6having a high reflection index, the light k2would be reflected back into the first mixing device2. After such repetitive reflection and mixing, a light with high uniformity can be produced.

In addition, to mix red, green, and blue lights into a uniform white light, each of the three component lights must be reflected inside the mixing assembly up to a specific number of times. If the mixing assembly contains only one mixing device, the mixing device must have a longer dimension to provide the specific number of reflections. To overcome the shortcoming of longer dimension and therefore larger form factor, the present embodiment utilizes a prism as the second mixing device3to alter the light transmission path so that, on one hand, the specific number of reflections is attainable to produce uniform light mixing and, on the other hand, the dimension of the first and third mixing devices2,4and, therefore, the overall dimension of the lighting system, can be reduced.

In summary, the present invention utilizes the light source module1to produce lights with the required color temperature. In other words, the color temperature can be adjusted freely based on requirements. Then, as shown inFIG. 4b, the present invention utilizes the mixing assembly to have the lights with the required color temperature reflected and mixed multiple times by the first mixing device2. The lights are then reversed by the second mixing device3into the third mixing device4, where the lights would undergo additional reflection and mixing. In the end, highly uniform white lights from mixing red-color, blue-color, and green-color lights are emitted out of the third mixing device4.

To verify the feasibility of the present invention, the following experiment is conducted.

Both the first and third mixing devices2,4have an inclination angle β of 10° and a height of 7.5 cm. The incident end21's aperture w11of the first mixing device2is 2.4 cm and the connecting end22's aperture w12is 5 cm. The connecting end41's aperture w21of the third mixing device4is 5 cm and the emitting end42's aperture w22is 7.6 cm. The light source module1is composed of an array of 36 LEDs, as shown inFIG. 5. Both the first (incident) and third (emitting) mixing devices2,4have a rectangular cross-section. Then, according to measurements made during the experiment, the luminous intensity of different colored lights emitted out of the mixing assembly is evenly distributed and has very limited variance. This result means, when the red-color, blue-color, and green-color LEDs in the light source module1are lighted simultaneously, a uniform white light is produced by the lighting system according to the present invention.

The measurement is conducted as shown inFIG. 6. Nine detectors7are located at the rim and center of an image plane's viewing area. Based on the colorimetry formulas, the data collected by each of the detectors7can be calculated into a (x, y) coordinate in the CIE 1931 chromaticity diagram. The measurement data from the detectors7and their corresponding (x, y) coordinates in the CIE 1931 chromaticity diagram are listed and plotted in Table 1 andFIG. 7. As shown inFIG. 7, the (x, y) coordinates are all clustered together in the CIE 1931 chromaticity diagram. This means that the white lights measured at the rim and center of the image plane's viewing area are almost identical.