Displays based on inorganic light-emitting diodes (LED) are considered as the most promising one among the display technologies for the next-generation The chip for LED display bears similar features to those currently in use for general lighting, but it size is shrunk to below 200 microns Thus, the advantages of high efficiency and long life span of conventional LED chips are inherited by miniaturized ones As the size gets smaller, the resolution enhances, but at the expense of elevating the complexity of fabrication In this review, we introduce two sorts of inorganic LED displays, namely relatively large and small varieties The mini-LEDs with chip sizes ranging from 100 to 200 μm have already been commercialized for backlight sources in consumer electronics applications The realized local diming can greatly improve the contrast ratio at relatively low energy consumptions The micro-LEDs with chip size less than 100 μm, still remain in the laboratory The full-color solution, one of the key technologies along with its three main components, red, green, and blue chips, as well color conversion, and optical lens synthesis, are introduced in detail Moreover, this review provides an account for contemporary technologies as well as a clear view of inorganic and miniaturized LED displays for the display community

Mini-LED and Micro-LED: Promising Candidates for the Next Generation Display Technology

Investigation on Entraining and Enhancing Human Circadian Rhythm in Closed Environments Using Daylight-Like LED Mixed Lighting

With the recent advances in photobiology research and light-emitting diode technology, lighting considering circadian effects and the potential health benefits attract much attention. In this study...

Spectral optimisation and a novel lighting-design space based on circadian stimulus

In this paper, we carry out the theoretical spectral optimization and perform experiments by varying temperature and electrical current primarily on one-phosphor-coated three-hump white light-emitting diode (LED) for healthy indoor or outdoor lighting by using the genetic algorithm (GA). White light with low circadian action factor (CAF) is propitious for bedroom lighting to help people relax and to promote sleep, whereas high CAF white light is beneficial for increasing working efficiency in the working place. We obtain low CAF or high CAF according to different application occasions (such as bedroom lighting or office lighting), good Commission Internationale de L’Eclairage color rendering index ( $R_{a}$ ) or Illumination Engineering Society of North America color fidelity index ( $R_{f}$ ), and color gamut index ( $R_{g}$ ) or other color performances, and possibly high luminous efficacy of radiation (LER, $K$ ) at various correlated color temperatures (CCTs) from 2700 to 6500 K. For instance, in the case of one-phosphor-coated three-hump white LEDs at CCT = 3000 K, the low CAF as 0.264 ( $R_{a}$ = 80, $R_{f}$ = 77, $R_{g}$ = 103, and $K$ = 350.0 lm/W) can be achieved, whereas that of standard light at the same CCT is 0.407. In addition, we also compare four types of three-hump white LEDs in performances of circadian action, luminous efficacy of radiation (LER), and color rendering. This paper can help both industry and academia understand the application of three-hump white LEDs in the healthy indoor or outdoor lighting.

Investigation on Three-Hump Phosphor-Coated White Light-Emitting Diodes for Healthy Lighting by Genetic Algorithm

Spectrally Stable Ultra‐Pure Blue Perovskite Light‐Emitting Diodes Boosted by Square‐Wave Alternating Voltage

A solution for multi-functional indoor light sources is proposed to achieve the new concept of healthy lighting. A remotely controllable light source that embodies a quadruple-chip light-emitting diode and driven by pulse-width-modulation currents is designed. Therefore, spectral power distributions (SPDs) of the light source can be readily controlled. An algorithm, namely the optical power ratio algorithm, is developed to select all suitable SPDs adapted for various applications. Principles of selection are based on those traditional visual indices, as well as on some non-visual parameters such as circadian action factor, circadian efficacy of radiation and circadian illuminance. We investigate in detail the correlation among these parameters and provide SPDs with both decent visual and non-visual performances for three typical cases. The study suggests some fundamental principles for designing healthy light sources, and can be regarded as a guide for designing indoor light sources of the next generation.

Multi-function indoor light sources based on light-emitting diodes-a solution for healthy lighting.

We introduce a new method for measuring the junction temperature of alternating current light-emitting diodes. This method employs a periodic bipolar voltage pulse signal as the input, and utilizes the amplitude of corresponding output current as the temperature sensitive parameter (TSP), of which a linear temperature dependence is proven in a prior experiment in this paper. On the basis of the TSP, we devise a detailed procedure—first, measure the thermal resistance of the package of ac-LEDs, which further contributes to the calculation of junction temperatures under various power inputs. Comparisons between values calculated by using this method and those obtained directly from a thermocouple indicate a decent accuracy of the former. The advantage of this method benefits from the stability of thermal resistance under different driving conditions that one could immediately obtain the junction temperature by measuring the electric and optical powers.

A Bipolar-Pulse Voltage Method for Junction Temperature Measurement of Alternating Current Light-Emitting Diodes

Outdoor light sources must guarantee excellent mesopic luminance (Lmes) for traffic safety at night. Here, we propose a solution to improve mesopic-related parameters, which include especially the scotopic/photopic ratio and the Lmes, of multi-chip light-emitting diode (LED) light sources. Generally, these sources are driven by pulse-width-modulation currents, and possess readily-controlled spectral power distributions (SPDs). An updated version of the optical power ratio algorithm developed in this article can select suitable overall SPDs and yield corresponding duty cycles to drive individual chips at different correlated-color temperatures and operating temperatures. Its accuracy and practicality are proven by experimental results. In addition, our study introduces a temperature-feedback technique that can instantly adjust duty cycles for each chip according to real-time operating temperatures in order to avoid undesirable color drifts at different operating temperatures. It can also be regarded as a model for practitioners who desire to improve the quality of outdoor light sources.

Improvements of mesopic luminance for light-emitting-diode-based outdoor light sources via tuning scotopic/photopic ratios.

Performance Enhancement of On-Chip Optical Switch and Memory Using Ge2sb2te5 Slot-Assisted Microring Resonator

The invention relates to an intelligent dimming toning method and a device for a multi-color LED illumination light source and relates to an LED illumination light source. The intelligent multi-color LED illumination light source is provided with a power source module, a driving control module and an LED illumination module, wherein the power source module is provided with an AC-DC unit and a DC-DC unit, the power source module is connected with a power source port of the driving control module, the driving control module is provided with a wideband antenna, a multi-mode radio frequency processing unit, a data storage unit, a single-chip microcomputer, a constant current driving unit, a power source port, a feedback port and a driving bus port, and the LED illumination module is provided with a distributed temperature sensor, a red light LED, a green light LED, a blue light LED and a white light LED. According to the intelligent multi-color LED illumination light source, compatibility of and support for the multi-mode wireless networking technology can be realized; on the basis of the white light LED, through collocation of the red, green and blue light LEDs, the color temperature of the mixed-color light is adjustable, high color rendering is realized, and no-lower-than-95 high color rendering indexes can be realized.

Honghui Zhu

Papers

Multi-function indoor light sources based on light-emitting diodes-a solution for healthy lighting.

A Bipolar-Pulse Voltage Method for Junction Temperature Measurement of Alternating Current Light-Emitting Diodes

Improvements of mesopic luminance for light-emitting-diode-based outdoor light sources via tuning scotopic/photopic ratios.

Performance Enhancement of On-Chip Optical Switch and Memory Using Ge2sb2te5 Slot-Assisted Microring Resonator

Intelligent dimming toning method and device for multi-color LED illumination light source