Shih-Hsin Ma

Effects of Volume Scattering Diffusers on the Color Variation of White Light LEDs

This study analyzed the variation of the correlated color temperature (CCT) of white light, which was emitted from Lambertian-type LEDs, and passed through a volume scattering diffuser (VSD). The tested VSD, fabricated by mixing scattering particles (PMMA) in glue (epoxy), exhibited various concentration weights of the scattering particles. Measurements showed that the CCT values decreased and the CCT variations exhibited oscillatory behavior, as the concentration of scattering particles increased. Furthermore, the results regarding CCT variation demonstrated that a higher CCT source is more sensitive to the concentration than a lower CCT source is, suggesting that the power loss of shorter-wavelength light is greater than that of longer-wavelength light, when the light passes through a VSD.

Generation of a uniform-square focal spot by a compound lens for solar concentration applications

This paper describes a compound lens for solar photovoltaic system applications, which is composed of a front aspheric or Fresnel surface and a back array of concave surfaces. In contrast to earlier designs, the proposed method can simultaneously focus and shape sun light into a uniform-square pattern on the solar cell. For a square solar cell, this approach can maximize the solar cells opto-electric conversion efficiency by enhancing the concentrated patterns uniformity. In this article, the theoretical models of the beam shaping focused lens is derived and then compared with experimental data. The tolerance in assembling the component of the concentrator is also analyzed and the corresponding simulation and experimental results are discussed in detail.

The application of laser triangulation method on the blind guidance

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.

Analyzing of light pattern uniformity in multi-chips LED lighting

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.

Study of CCT varying by volume scattering diffuser with moving and rotating white light LED

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.

LED collimation module for time sequential back light system

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.

Blind guidance system based on laser triangulation

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.

Effects of pitch and shape for diffraction grating in LED fog lamp

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.

The design of beam shaping focused lens applied in solar energy concentration

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.

LED phototherapy system in skin treatment and detecting

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.