In this paper, we present our investigation into the prevention of blue-light leakage in phosphor-converted white LEDs through a passive approach. Our study primarily focuses on the application and optimization of a specific thermochromic material known as Crystal Nano Cellulose (CNC). We integrated CNC within the epoxy lens of white LEDs. Importantly, under normal operating conditions, CNC minimally affects the optical properties of the emitted white light. However, in instances of overheating where blue-light leakage occurs, the temperature rise induces a darkening effect in CNC. By incorporating CNC as a responsive material in the design of white LEDs, our study offers a practical and efficient solution to address the adverse effects of blue-light leakage resulting from overheating. This enhancement not only improves the safety and comfort for users but also serves as an early warning mechanism for the aging of phosphor-converted white LEDs.
In this study, we use 30 mini-LED arrays as the light source of the bike lamp. A single reflector with 68 segments to project vehicle low beam and high beam with the use of a GaN-based mini-LED matrix, which is a 30 LED dies array. The design of the reflector is based on light field technology in considering etendue from the light source across the segments. The group of the segments with smaller etendue from the LED dies in the bottom 2 rows are used to project low beams. When the other LED dies are turned on, the reflector will project light upward and form the high beam. The selection of the turn-on LED dies in the mini-LED matrix can adjust the width of the illumination pattern so that an adaptive low/high beam can be performed.
We perform the mid-field model of a UV-C LED with an arranged wavelength of around 275 nm by comparing the 2-dimension (2-D) gray-level image captured by a monochromatic CMOS and the corresponding simulated irradiance pattern. Owing to UV-C light, we propose using a fluorescent film to absorb UV-C light and re-emit light at a longer wavelength so that the 2-D gray level image can be captured. The calibration to approach the corrected gray level of image is presented. Consequently, we obtain the precise mid-field light source model. Moreover, the model is also applied for dome lens design and then compares the optical behavior with fabricated samples in measurement to evaluate its validity.
We performed the simulation and experiment to investigate the influence of Zirconium dioxide (Zirconia, ZrO2) particles on the optical properties of phosphor converted white LED (pcW-LED). An efficient optical model was developed and applied to the incorporation diffuse particle of ZrO2 into a hemisphere package containing YAG phosphors. The optical properties (chromaticity, packaging efficiency) were estimated as a function of phosphor and ZrO2 particles, through the calculation of effective radius, refractive index, and absorption and conversion efficiency, in a range of correlated color temperature 4500 K to 6500 K. In the same way, the amount of phosphor and ZrO2 can be calculated accurately to obtain a targeted optical property in a hemisphere LED design. Especially, the angular distribution of CCT was also diminished, and even almost inexistent for low CCT design. In addition, the adding of ZrO2 particles allows clearly decreasing the amount of phosphor for an identical target CCT. It is really suitable in the context of decreasing the amount of phosphor or in some applications where the color uniformity is an important parameter, like indoor down-lighting.
We performed the simulation of white LEDs packaging with different chessboard structures of white light
converting phosphor layer covered on GaN die chip. Three different types of chessboard structures are called type 1,
type 2 and type 3, respectively. The result of investigation according to the phosphor thickness show the increasing
of thickness of phosphor layer are, the decreasing of output blue light power are. Meanwhile, the changes of yellow
light are neglect. Type 3 shows highest packaging efficiency of 74.3 % compares with packaging efficiency of type
2 and type 1 (72.5 % and 71.3 %, respectively). Type 3 also shows the most effect of forward light. Attention that
the type 3 chessboard structure gets packaging efficiency of 74.3 % at color temperature of daylight as well as high
saving of phosphor amount. The color temperatures of three types of chessboard structure are higher than 5000 K, so
they are suitable for lighting purpose. The angular correlate color temperature deviation (ACCTD) of type 1, type 2
and type 3 are 6500K, 11500K and 17000K, respectively.
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