Browsing by Author "Zheng, Lili"

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Assessment and Optimization of the Circadian Performance of Smartphone-Based Virtual Reality Displays
(2019-01-01)
Wu, Tingzhu
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Liang, Shijie
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Zheng, Lili
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Lin, Yue
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Guo, Ziquan
The non-visual effects of blue light in displays mean that excessive use of smartphones can disturb the human circadian rhythm. Thus, the impact of virtual reality (VR) headsets, which are worn closer to the human eye, may be even more serious. In this paper, based on non-visual parameters, such as the circadian action factor (CAF) and circadian illuminance, the circadian performance of smartphone-based VR displays is quantitatively evaluated by an evaluation system we designed. Moreover, we investigate the improvements in the circadian performance of VR headsets resulting from three practical methods for reducing the blue light content. Finally, a theoretical method of shifting the green-light wavelength of the screen close to 555 nm to optimize the CAF of VR headsets is proposed. Overall, the results of this paper are of significant value in quantifying the effects of VR displays on circadian rhythms and improving the safety of VR headsets with regard to human health.
Research on a Camera-Based Microscopic Imaging System to Inspect the Surface Luminance of the Micro-LED Array
(2018-01-01)
Zheng, Lili
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Guo, Ziquan
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Yan, Wei
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Lin, Yue
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Lu, Yijun
A majority of luminance measurement systems are currently focused on measuring the total luminance of light-emitting diodes (LEDs). It has largely limit its application on micro-LEDs, which require capturing the microscopic surface luminance. In order to study the microscopic characteristics of micro-LED displays, in this paper we propose a practical method that can accurately measure the luminance of a whole micro-LED array and even the surface luminance distribution of any single micro-led chip on the array. The essentials of this method are a high-precision complementary metal oxide semiconductor camera and a self-made data processing algorithm. Results show that the maximum error of the luminance measurement is less than 8%, which can prove the accuracy of the method. The metrical wavelength range and the accuracy of system can be dynamically set according to the camera and microscope. Endowed with ultrahigh dynamic ranges, this system proves its competency for evaluating the spatially resolved distribution of luminance for high brightness micro-LEDs.
The Impact of Luminous Properties of Red, Green, and Blue Mini-LEDs on the Color Gamut
(2019-05-01)
Guo, Weijie
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Chen, Nan
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Lu, Hao
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Su, Changwen
;
Lin, Yue
Color gamut is of the paramount importance in the display. Light-current-voltage(L-I-V) characteristics of red, green, and blue flip-chip mini-light-emitting diodes (LEDs) (100 mu m x 200 mu m) are investigated at temperatures similar to the operational temperatures. Both the ideality factor and the temperature dependence of external quantum efficiency (EQE) suggest that the nonradiative loss in red mini-LED is higher. We also illustrate the intensive lateral luminous intensity fluctuation for red mini-LED under the over-driving current by capturing the spatial emission mapping. The influence of temperature and driving current on the chromaticity coordinates of mini-LEDs is determined. Furthermore, we propose a drive-current algorithm to maximize the color gamut of the trichromatic mixed light at different temperatures. The results indicate that, for the application of self-emitting mini-LED displays, the maximum color gamut is more sensitive to green emission, whereas enhancing the radiative recombination in red mini-LED could contribute a lot to the improvement on net performance.