We present the results of this study of a calculation model built for predicting the spectrum of white-light LED (WLLED) with different concentration formula of three kinds of the phosphor. First, we analyze the spectrum of the blue light LED with different penetrating concentrations of the phosphor. Next, we analyze the emission spectrum after absorption of blue light by the phosphor and the re-absorption effect. Then, we introduce the re-absorption effect into the superimposed spectrum of blue light and the emitting light. Finally, we compare the superimposed spectrum with the experimental result. By this method, we can predict the behavior of the WLLED, such as optical efficiency, chromaticity coordinates, correlated color temperature (CCT), and color rendering. Thus, we obtain the weight ratio of the multi-color mixed phosphor (MCP) of high color rendering WLLED.
Collimation lenses for light-emitting diode (LED) light sources have been widely used in lighting engineering. In this study, a collimated LED light source was developed for a color liquid-crystal display backlight, which is driven using a two-field driving scheme to display color. A color-separation backlight that involves using the designed collimation modules possesses several advantages such as low volume, elimination of dye color filters, high feasibility with conventional ultraprecision machining processes, and a wide color gamut.
Multiple chips are often bonded in a small single package of LED to obtain higher light flux output. However, the nonuniformity of light pattern always exists due to the high order collimating lamp, which uses the MCLED (Multi-chips LED) as the source. In this paper, the light pattern uniformity of lamp composed of four-in-one MCLED, whose thickness of phosphor layer and the length of lamp are respectively 0.1 mm and 10 mm, is simulated and analyzed. The ray tracing simulated by computer with varying the spacing of chips, concentration of phosphor, shape of lamp, and the corresponding uniformity of light pattern will be analyzed and discussed in detail.
In this study, a collimated LED light source has been developed as a colorful liquid crystal display backlight, which is driven by a two-field driving scheme to display color. In each field, the angular rays of two colors from LEDs are collimated by a collimation lens, redirected by a light guide and converged by a cylindrical-lens array to map into corresponding sub-pixel positions for efficiently displaying color image. The simulation results of the backlight module and the corresponding experimental results will be discussed in detail.
In this study, the corrected color temperature (CCT) of white light, which originates from a white light LED (WLLED) and passes through a volume-scattering diffuser (VSD), is investigated. The VSD with thickness of 2mm is fabricated by mixing the 2um-sized PMMA scattering particles and the epoxy glue with different concentration values. Moreover, in order to understand the influences of the illuminated area and the scattering path of VSD on CCT values, the bulletheaded and lambertian-type WLLEDs are assembled for different positions and distinct orientations along the optical axis in a black cavity. A detailed comparison between results regarding the white light with and without passing through the VSD is offered. The results of this research will help to improve the colorful consistency of the LED lamps which use diffusers.
We propose a new guidance system for the blind. An optical triangulation method is used in the system. The main components of the proposed system comprise of a notebook computer, a camera, and two laser modules. The track image of the light beam on the ground or on the object is captured by the camera and then the image is sent to the notebook computer for further processing and analysis. Using a developed signal-processing algorithm, our system can determine the object width and the distance between the object and the blind person through the calculation of the light line positions on the image. A series of feasibility tests of the developed blind guidance system were conducted. The experimental results show that the distance between the test object and the blind can be measured with a standard deviation of less than 8.5% within the range of 40 and 130 cm, while the test object width can be measured with a standard deviation of less than 4.5% within the range of 40 and 130 cm. The application potential of the designed system to the blind guidance can be expected.
The characteristics of light-emitting diodes (LEDs) that make them energy-efficient and long-lasting light source for
general illumination have attracted a great attention from the lighting industry and commercial market. As everyone
know LEDs have the advantages of environmental protection, long lifetime, fast response time (μs), low voltage and
good mechanical properties. Their high luminance and the wide region of the dominant wavelengths within the entire
visible spectrum mean that people have high anticipations for the applications of LEDs. The output lighting from
reflector in the traditional fog lamp was required to fit the standard of the ECE R19 F3 regulation. Therefore, this study
investigated the effects of pitch and angle for a diffraction grating in LED fog lamp. The light pattern of fog lamp must
be satisfied ECE regulations, so a design of diffraction grating to shift down the lighting was required. There are three
LEDs (Cree XLamp XPE LEDs) as the light source in the fog lamp for the illumination efficiency. Then, an optimal
simulation of diffraction grating was done for the pitch and angle of the diffraction grating at the test distance of 25
meters. The best pitch and angle was 2mm and 60 degree for the grating shape of wedge type.
In this paper, we proposed a new configuration of concentrator in solar PV system. A special optical system in the
concentrator used in focusing sun light to solar cell is proposed, the system compose of an aspherical surface and a
specific diffusing surface. The uniform-squared light pattern is obtained on the solar cell, the shape and size of light
pattern can be modulated by the parameters of the diffusing surface. In order to decrease the weight of the lens, the
concentrator in Fresnel lens type is built at last. Besides, the optical efficiencies formed by the aspherical concentrator
and Fresnel concentrator are about 92% and 77%, the concentrations are about 720mW/mm2 and 640mW/mm2, and the
acceptance angles are about 0.35° and 0.30°, respectively. The tolerances in assembling the component of the
concentrator are also discussed in detail.
A new apparatus for blind-guide is proposed in this paper. Optical triangulation method was used to realize the system.
The main components comprise a notebook computer, a camera and two laser modules. One laser module emits a light
line beam on the vertical axis. Another laser module emits a light line beam on the tilt horizontal axis. The track of the
light line beam on the ground or on the object is captured by the camera, and the image is sent to the notebook computer
for calculation. The system can calculate the object width and the distance between the object and the blind in terms of
the light line positions on the image. Based on the experiment, the distance between the test object and the blind can be
measured with a standard deviation of less than 3% within the range of 60 to 150 cm. The test object width can be
measured with a standard deviation of less than 1% within the range of 60 to 150 cm. For saving the power consumption,
the laser modules are switched on/off with a trigger pulse. And for reducing the complex computation, the two laser
modules are switched on alternately. Besides this, a band pass filter is used to filter out the signal except the specific
laser light, which can increase the signal to noise ratio.
In this research, a new module of skin treatment has been proposed. The 40 pieces of red and 36 pieces of yellow LEDs
are utilized to be the light sources in treatment the cracks and corrosions on skin, and the 4 pieces of white light LEDs
are applied in lighting on skin. In addition, the image of skin could be obtained by a CCD webcam, and the skin
inspection will be determined by number of pores in images. Finally, the good experimental results have been obtained
in human body.
A single-chip white light LED is commonly modeled by considering the phosphor coating as a homogeneous
Lambertian light source. However, this approach leads to an incorrect optical simulation of phosphor-coated multi-chip
LEDs due to the presence of a previously unreported spatial distribution of emission spots across the phosphor layer. We
introduce "weighting" factors based on position-dependent light strength across the phosphor surface in order to improve
the model accuracy. Following the modeling algorithm in the mid-field region, we have built up a precise and practical
optical model by using Monte Carlo ray tracing and weighting factors. We measure the LED radiation distribution at
several representative distances to test the model performance. In all cases, the accuracy is higher than 99.5% in
normalized cross correlation between the simulated pattern and experimental measurement.
Proc. SPIE. 6342, International Optical Design Conference 2006
KEYWORDS: Light sources, Light emitting diodes, LED lighting, Scattering, Light scattering, 3D modeling, Monte Carlo methods, Distance measurement, Light sources and illumination, Charge-coupled devices
In this paper, we propose a novel LED modeling algorithm for precise 3-D light pattern simulation. Normalized cross correlation is proposed to to verify the validity of the simulation in 1-D intensity pattern as well as 2-D irradiance pattern in various mid-field distances. The model is demonstrated to obtain more than 98% in normalized cross correlation between the simulation light pattern and experimental measurement for a TIP LED emitter by Lumileds.
We propose an algorithm for a receiver, which is attached on a moving carrier, to detect the laser beam for free space communication. The characteristic of the receiver is that it can detect the transmitted signal in a large view angle and with a large cross area. We have theoretically calculated the relative detecting light intensity with respect to the incident angle. In addition, the scattering characteristic of a ground glass, which serves as a diffuser, has been studied. Finally, we design a receiver with a view angle larger than 30o. For a special ground glass, the angular tolerance of the receiver is as large as 120 o.
We propose a new holographic multiplexing technique in LiNbO3 with 90° geometry. The advanced concept of polarization-multiplexed holographic memory is based on photorefractive effect and photovoltaic effect. The holographic gratings are constructed in the crystal using two writing beams with isotropic and anisotropic polarizaiton recording. Even mutually orthogonal polarized waves can be used in holographic storage. The polarization multiplexing technique can be accompanied with other multiplexing method in the holographic storage, and we can increase the storage capacity doubly.