1. Field of the Invention
The invention discloses a method for mixing light, particularly a methodology for multispectral mixing optimization of LEDs clusters.
2. Description of the Prior Art
The progress in Light-emitting diodes (LEDs) technology has been breathtaking during the last few decades. At this time, great technological advances in LEDs are profoundly changing the way light was generated. In contrast to many conventional light sources, LEDs not only have the potential of converting electricity to light with near-unit efficiency, but also offer impressive controllability of their spatial distribution, temporal modulation, and polarization property. With an arrangement of multispectral LEDs, the LEDs cluster could particularly have the capability of manipulating its synthesized spectral power distributions (SPDs). Such intelligent light sources could be adjusted according to different operational environments and requirements. As a result, tremendous properties of LEDs or LEDs cluster lead to great benefits across a wide field of applications, including lighting, transportation, communication, imaging, agriculture, and medicine.
In general, the mixing of multiple spectra based on LEDs can be accomplished by using (i) additive mixing of two or more single-color LED chips (LED-primary-based approach), (ii) wavelength-conversion via using phosphors or other materials (LED-plus-phosphor-based approach), and (iii) a hybrid approach composed of (i) and (ii). It is well known that a basic trichromatic mixing by LED-primary-based approach is mathematically critical determined, in which the three emission sources are predetermined. In fact, the selections of emission band {circumflex over (λ)} provide additional degrees of freedom, whose values will be highly relevant to the operational purposes. For example, a trichromatic combination of {circumflex over (λ)}=450-455 nm (spectral width Δλ=5 kT), {circumflex over (λ)}2=525-535 nm (Δλ=5 kT), and {circumflex over (λ)}2=600-615 nm (Δλ=5 kT) is very favorable in terms of high color rendering lighting, resulting in a high CRI value in the range of 80-85.
It is generalized that the condition by considering a synthesized SPD composed of n undetermined emission bands, used for certain purpose with specific chromaticity point. The problem is no longer critically determined but underdetermined, which is equivalent to subjecting the 2n-dimensional parameter space {{circumflex over (λ)}1, . . . , {circumflex over (λ)}n, I1, . . . , In}, composed of emission bands {circumflex over (λ)} and drive currents I, to three color-mixing constrains. In other words, an optimization happens in searching the best location, composed by two n-dimensional vectors {{circumflex over (λ)}1, . . . , {circumflex over (λ)}n} and {I1, . . . , In}, on the hypersurface with dimensionality 2n−3. Where the best location represents that composed spectrum provides the maximal benefit to the purposes. It could mathematically write the solution in a form as:
arg max[{MF,cons}{{circumflex over (λ)}1, . . . ,{circumflex over (λ)}n,I1, . . . ,In}]
where MF is the merit function of the purposes. The term cons indicates three mixing constrains. In 2002, A. {hacek over (Z)}ukauskasa et al. solved the above problem for general lighting applications. For simplicity, each emission band was assumed as a single Gaussian line with Δλ=6 kT. The optimal LEDs clusters for n=2, 3, 4, and 5 were analyzed. Those results address the fundamental tradeoff between the luminous efficacy of radiance LER and the color rendering index CRI, which has the potential to provide a useful guide in the design of a polychromatic system.
However, as the trend of higher efficiencies in phosphor-converted white LEDs continues, the possible hybrid designs increases as well. State of the art tetrachromatic hybrid design (neutral-white/red/green/blue), proposed by G. He et al., can realize a white composite light with high color rendering property as well as high luminous efficiency, but due to the assumption of constant thermal environment (i.e. only consider the dependence of current on source model) a widespread diffusion of multichip LED cluster is not provided. To date, a general SPD synthesizing for practical LED clusters, especially for those with the number of sources >3, is still subject of discussion. Main obstacle lies in the present lack of complete methodology, which can systematically and efficiently optimize SPD for an underdetermined system in consideration of current and temperature dependences
In order to overcome current implementation barriers of LEDs cluster, we make an attempt to borrow design techniques from a conventional lens system to develop a general mixing approach in a more complete treatment. The idea arose from the recognition of the fundamental similarity of multi-chip LEDs system and conventional lens system. The whole design flow in all aspects can be closely analogous to a lens design process that has long been developed, by which the spectrum of an LED cluster can be optimized by going through every step of the proposed scheme.
The main purpose of the invention is to provide a method for mixing light of LED cluster, which can be used in the white lighting emitting diode field.
The adjustable LED of the invention mixes more than two kinds of LED light sources to obtain emitted light with high color rendering index or high luminous efficiency.
The invention provides a genetic algorithm and uses the established multiple LED spectrum database to create a mixing light mode achieving color temperature condition, in order to obtain the global maximum of database, so as to control the LED cluster system.
The adjustable LED light source of the invention is able to be introduced into the modulation of common lighting and light environment. The applied field of the invention is able to comprise the LED field, the fluorescence light source field (such as LED cluster, fluorescence light source array, and fluorescence lamp array), and the other light source field etc.
Therefore, the advantage and spirit of the invention can be understood further by the following detail description of invention and attached figures.
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
a),
The invention relates to a method for mixing light of LED cluster, which is able to optimize the LED cluster to obtain the best luminance efficacy of radiation (LER), color rendering index (CRI), or color quality scale (CQS). The LED with multiple wave bands is combined to form the spectrum with objective color temperature. Evaluate the color quality scale (CQS) of color rendering property and the luminance efficacy of radiation and use the continuous genetic algorithm to optimize the most suitable combination ratio for the intensity of LED, adjust the spectrum of objective color temperature and possess the best evaluation index and luminance efficacy of radiation for assess the color rendering property of light source.
The design principle of the invention regards the LED cluster as a lens. Various specific conditions of the LED cluster are considered as important parameters for the design of lens. For example, when the LED with single color space considered as a lens unit, its corresponding relation is defined as:
The LED power determined by its curvature and refractive index can be conceptually analogous to the emitting luminous flux of LEDs determined by the driven current and luminous efficiency, respectively
As mixing a number of LEDs, the additive mixing by the dichromatic LED-primary based approach is equivalent to two singlet lenses. Likewise, the LED-plus-phosphor based approach can be regarded as a cemented doublet (dichromatic) or triplet (trichromatic), dependent on the number of exciting peak wavelength.
The invention relates to a method for mixing light of LED cluster, which is shown in the first preferred embodiment in
After the spectrum for the mixing light of the color coordinate is achieved, the calculation is conducted in accordance with the following merit function (1):
ƒ=w×CQS+(1−w)×LE,
subject to the constrain: weight wε[0,1], (1)
In the merit function (1), w represents the weight ratio, CQS represents the color rendering index (saturation level of color), and LE represents the luminance efficacy (lm/W).
It can be solved to obtain the values of color quality scale (CQS) and the luminous efficiency (LE) for every set of mixing light, and the best solution of color rendering index and luminous efficiency.
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The core mechanism of the invention is the continuous genetic algorithm (CGA). Its concept is to imitate the natural evolution for the calculation. The calculation mechanism mainly includes: reformation, mutation, and selection. The genetic algorithm uses random points searching to obtain the solution, thus the awkward situation of only local maximum will be avoided. The genetic algorithm mainly encodes the parameters into the data structure suitable for the calculation of genetic algorithm. Thus it will not be restricted by the continuity of parameter in searching analysis. Thus it can be applied to different optimization problems. The initial value of genetic algorithm depends on the problem. The random selection of genetic algorithm can obtain diversified initial value in the group, thus the random and global solution can be obtained for the merit function. Compared to other algorithms, the genetic algorithm can get the global maximum through the effective continuous evaluation of variance amount to avoid rapid convergence and constraint.
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Collecting the default values: Obtaining better initial condition through previous accumulated experience; Collecting the literature: Referring to the published research and literature to obtain better setup value; and collecting the published patents: Referring to the published patents to obtain better setup value.
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Where X, Y, Z in equation (2) represent tristimulus values specified in the International Commission on Illumination (CIE) system. The error defined in the mathematical equation (2) is 0.01 color unit, because the human eyes are relatively tardy to the vision response of high illumination.
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Blue spectrum=470 nm,
green spectrum=525 nm,
amber spectrum=589 nm, and
red spectrum=630 nm.
Through the pulse width modulation (PWM) for a phosphor based cool white LED (Philips TX-213), every LED is able to produce 128 levels of gray-level variation, and accord with the linear superposition and addition of color modulation. Thus from
In addition, except the above-mentioned constant light source array, the applied field of the invention is able to comprise the fluorescence light source field, such as LED cluster, fluorescence light source array, and fluorescence lamp array, as well as the other light source field etc. . . .
It is understood that various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of this invention. Accordingly, it is not intended that the scope of the claims appended hereto be limited to the description as set forth herein, but rather that the claims be construed as encompassing all the features of patentable novelty that reside in the present invention, including all features that would be treated as equivalents thereof by those skilled in the art to which this invention pertains.
Number | Date | Country | Kind |
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100135174 A | Sep 2011 | TW | national |
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Entry |
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Ming-Chin Chien and Chung-Hao Tien; Cluster LEDs mixing optimization by lens design techniques; Jun. 9, 2011; Publish: Optics Express. |
Number | Date | Country | |
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20130082622 A1 | Apr 2013 | US |