DE102011106209A1 - LED lighting device, has luminescence conversion element absorbing portion of blue light and converting blue light into secondary light, and additional set of light sources constructed of LEDs with wavelength greater than preset value - Google Patents

Abstract

The device has a set of light sources constructed of blue LEDs with an added luminescence conversion element, where blue light comprises predominating wavelength in the region between 430 nanometer (nm) and 460 nm. The luminescence conversion element absorbs portion of the blue light and converts the blue light into secondary light with peak wavelength ranging between 520 nm and 545 nm. Additional set of light sources is constructed of LEDs with predominating wavelength greater than 600 nm.

Description

1. FIELD OF THE INVENTION

The invention relates to a light emitting diode (LED) lighting device comprising a plurality of LED devices and characterized by the mixing of a first light source, a second light source and a third light source for producing a final light mixture having good color rendering properties and which color coordinates or close to Planck's black spotlight curve.

2. State of the art

Optoelectronic devices, such as LEDs, are widely used in today's world, especially for lighting and signaling devices. Conventional LEDs are inherently capable of producing saturated colors, both at long wavelengths, such as red, and at shorter wavelengths, such as blue, at the other end of the spectrum, depending on the semiconductor material used for fabrication of the LED chip is used. The materials GaP and AlInGaP are commonly used to produce colors in the red, orange and yellow regions of the spectrum. For blue, however, GaN and InGaN are used. These saturated colors can also be blended to create a wide range of colors. For example, red, green and blue can be mixed in a certain ratio to produce white. This procedure has been described several times in the prior art.

As the range of application for LEDs continues to increase, there is a need for an ever-expanding range of colors, particularly colors whose coordinates are at or near Planck's black spotlight curve. This is essential because most of today's light sources emit light in this color range. Furthermore, these light sources provide light with very good color rendering properties.

One approach to meeting this need is to use a luminescence conversion element. Such a method is described in Höhn et al. in the U.S. Patent 6,066,861 , According to this prior art, a method is described which uses a luminescence conversion element to convert a portion of a first wavelength emitted by a semiconductor body to a longer radiated wavelength. This makes it possible to manufacture a device which emits polychromatic light, in particular white light, with a single light-emitting semiconductor chip. With the correct primary light source and correct choice of the luminescence conversion element, a light mixture with color coordinates on or close to the Planck black radiator curve can be produced at the end.

However, such methods can not produce light with good color rendering properties. The color rendering index (CRI) is typically used to measure the color rendering characteristics of a light source. The CRI provides a relative measure of the color rendering of a lighting system compared to that of a blackbody. An ideal light source would have a CRI of 100. Such a light source is always preferable. For example, daylight has the highest CRI of 100, while fluorescent lamps have a CRI of between 70 and 80.

On the other hand, typical blue LEDs with an added luminescence conversion element have only a CRI in the range between 60 and 75. For typical lighting applications, a CRI of between 75 and 90 is required for comfortable viewing to the human eye and optimal color rendition. There are many components of color components that are absent in the converted radiated light, especially in the region of higher wavelengths between 600 nm and 700 nm. Thus, one of the methods for enhancing the color rendition of blue LEDs with added luminescence conversion element therein is red LEDs second To introduce light source in the lighting device. This procedure is in the U.S. Patent 7,213,940 described.

The U.S. Patent 7,213,940 describes a lighting device comprising a first and a second group of solid state illuminating emitters which emit light having a predominant wavelength each in the range between 430 nm and 480 nm and in the range between 600 nm and 630 nm; and a first group of phosphors which emit light having a predominant wavelength in the range between 555 nm and 585 nm. This particular group of phosphors is also commonly referred to as yellow-green phosphors, due to the color of the emitted light. Materials that can be used to make such phosphors include yttrium aluminum garnet (YAG), terbium aluminum garnet (TAG), etc.

The present specification is intended to describe an alternative method of producing a light mixture, yet with good color rendering properties.

3. DESCRIPTION OF THE DRAWINGS

In the accompanying drawings show:

1 the CIE standard color chart showing the Planckian black spotlight curve;

2 the typical color spectrum of blue LEDs with an added luminescence conversion element;

3 a typical diagram of the emission spectrum of the luminescence conversion element;

4 a typical diagram of the color spectrum of the mixed light from the blue LEDS and the emission of the luminescence conversion element;

5 a typical diagram of the color spectrum of the mixed light from the lighting device;

6 the schematic representation of the first exemplary embodiment of an LED lamp according to the invention;

7 the schematic representation of the first exemplary embodiment of the components and the circuit board according to the invention.

4. DETAILED DESCRIPTION

The invention relates to a light emitting diode (LED) lighting device comprising a plurality of LED components, and characterized by the mixing of a first light source, a second light source and a third light source for producing a final light mixture, which has good color rendering properties and which has color coordinates on or close to the Planck black radiator curve, as shown in FIG 1 ,

Blue LEDs with added luminescence conversion element are typically used as the first light source for most current LED lighting devices. Such a light source can produce colors with color coordinates on or close to the Planckian black spotlight curve. A typical color spectrum of such a light source is in 2 shown. Although such a light source is capable of producing the desired color for most applications, color rendering is usually below expectations.

According to the present invention, a light emitting diode (LED) light emitting device having good color reproduction comprises a plurality of LED devices, and is characterized by mixing a first group of light sources composed of blue LEDs with an added luminescence conversion element, the blue light having a dominant wavelength in the range between 430 nm and 460 nm, and wherein the luminescence conversion element absorbs a portion of the blue light and converts it into a secondary light having a wavelength peak in the range between 520 nm and 545 nm; and a second group of light sources constructed of LEDs having a dominant wavelength in the range between 600 nm and 610 nm; and a third group of light sources composed of LEDs with a dominant wavelength in the range between 615 nm and 625 nm.

The first group of light sources is constructed of blue LEDs with an added luminescence conversion element. The blue LEDs may be made of a nitride compound semiconductor, such as InGaN or GaN doped with impurities. The blue LEDs are selected such that the emitted wavelength is capable of being absorbed by the luminescence conversion element. According to the present invention, the blue LEDs have a dominant wavelength in the range between 430 nm and 460 nm and the luminescence conversion element absorbs a portion of this blue light and converts it into a secondary light having a wavelength peak in the range between 520 nm and 545 nm.

A typical emission spectrum of such a luminescence conversion element is in 3 shown. Such a luminescence conversion element would absorb a portion of the blue light and subsequently emit a secondary light having a wavelength peak in the range between 520 nm and 545 nm. The secondary emission will have a typical half power bandwidth between about 60 nm and 100 nm. Such a luminescence conversion element is also commonly known as a green phosphor due to the color emitted by the phosphor. A typical material composition for such a luminescence conversion element includes silicates activated with europium and rare earth doped garnets activated with cerium. These materials prove to be very efficient at converting light as compared to others, since the emitted wavelengths are in the range in which the human eye has the greatest sensitivity.

The mixed light from the blue LEDs and the emission of the luminescence conversion element would have a typical color spectrum, as in 4 shown. The color of the mixed light would be a very strong shade of green to the viewer, and it certainly would not be suitable for general lighting applications. To produce white light with color coordinates on or near the Planck black-emitter curve, which is suitable for general illumination, two further groups of light sources are required. The second group of light sources constructed of LEDs should have a dominant wavelength in the range between 600 nm and 610 nm and a third group of light sources constructed of LEDs should have a dominant wavelength in the range between 615 nm and 625 nm. Both groups of LEDs may be made of a compound semiconductor material, such as AlInGaP and GaP. The mixing ratio with respect to the output light between the three groups of light sources is typically in a range between 55% and 75%, between 10% and 20%, and between 20% and 30%. This mixture could produce white light with color coordinates on or close to the Planck black radiator curve. By varying the color spectrum or the wavelength of the three light sources and the mixing ratio for each group, the color coordinates for the final mixture could be varied along the Planck black radiator curve. The typical color spectrum of the final mixed light is in 5 shown. Such a light source produces good color rendering characteristics and has a typical CRI in the range between 75 and 90. This CRI range is suitable for general lighting applications.

6 shows a schematic representation of the first exemplary embodiment of an LED lamp according to the invention. The LED lamp has a housing outside 1 on. This housing may be made of metal, such as aluminum or cast iron. It can also be molded from conventional plastic, such as ABS. The light sources are on a printed circuit board 2 (PCB) constructed. 7 shows a typical layout of the circuit board, wherein the light sources are mounted. A group of blue LEDs with an added luminescence conversion element 3 is typically used as the first light source. The blue LEDs have a dominant wavelength in the range between 430 nm and 460 nm and the luminescence conversion element absorbs a portion of the blue light and converts it into secondary light having a wavelength peak in the range between 520 nm and 545 nm. This group of light sources typically produces a high total luminous flux in the range between 400 lumens and 1000 lumens. Several of these light sources are incorporated in an electrical circuit arrangement such that an electrical connection can be made. In the matrix of the first light source, LEDs having a dominant wavelength between 615 nm and 625 nm and between 600 nm and 610 nm are second light sources 4 in the electrical circuitry, such that the color rendering index (CRI) of the light can be improved. The second light sources will typically provide between about 25% and 40% of the first light source. In this mixing ratio, the generated white light will have color coordinates on or close to the Planck black radiator curve. The CRI of the lighting device would also be approximately in the range between 75 and 90.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 6066861 [0004]
• US 7213940 [0006, 0007]

Claims (6)

A light emitting diode (LED) light emitting device having good color rendering comprising a plurality of LED devices and characterized by mixing: a first group of light sources constructed of blue LEDs with an added luminescence conversion element, the blue light having a dominant wavelength in the range between 430 nm and 460 nm, and wherein the luminescence conversion element absorbs a portion of that blue light and converts it to a secondary light has a wavelength peak in the range between 520 nm and 545 nm; and another group of longer wavelength light sources constructed of LEDs with a dominant wavelength greater than 600 nm. A lighting device according to claim 1, wherein the longer wavelength group comprises: a group of light sources composed of LEDs with a dominant wavelength in the range between 600 nm and 610 nm; and another group of light sources composed of LEDs with a dominant wavelength in the range between 615 nm and 625 nm. A lighting device according to claim 1, wherein the color of the mixed light has color coordinates on or close to the Planck black radiator curve. A lighting device according to claim 2, wherein the mixing ratio with respect to the output light between the three groups of light sources is typically in the range between 55% and 75%, between 10% and 20%, and between 20% and 30%. A lighting device according to claim 1, wherein the color rendering index is in the range between 75 and 90. A light emitting diode (LED) light emitting device having good color rendering comprising a plurality of LED devices and characterized by mixing: a first group of light sources constructed of blue LEDs with an added luminescence conversion element, the blue light having a dominant wavelength in the range between 430 nm and 460 nm, and wherein the luminescence conversion element absorbs a portion of that blue light and converts it to a secondary light has a wavelength peak in the range between 520 nm and 545 nm; a second group of light sources composed of LEDs having a dominant wavelength in the range between 600 nm and 610 nm; and a third group of light sources composed of LEDs with a dominant wavelength in the range between 615 nm and 625 nm.

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