• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.28 no.10
• /
• pp.676-681
• /
• 2015

Recently many studies being carried out to increase the light efficiency of LED. The external quantum efficiency of LED, generally the light efficiency, is determined by the internal quantum efficiency and the light extraction efficiency. The internal quantum efficiency of LED was already reached to more than 90%, but the light extraction efficiency is still insufficient compared with the internal quantum efficiency because the total internal reflection is generated in the interface between the LED chip and air. Thus, we studied about flip chip LED with PSS and performed the optical simulation which find more optimized PSS for flip chip LED to increase the light extraction efficiency. Decreasing of the total internal reflection and effect of diffused reflection according to PSS improved the light extraction efficiency. To get more higher the efficiency, we simulated flip chip with PSS that the parameters are arrangement, edge spacing, radius, height and shape of PSS.

• The Journal of the Convergence on Culture Technology
• /
• v.7 no.1
• /
• pp.564-569
• /
• 2021

In this paper, for the typical LED and the tilted LED, when there is no electrode, when 20% absorption (80% reflection) occurs at the electrode, and when 60% absorption (40% reflection) occurs at the electrode, the effect of the absorption at the electrode and the height of the active region on the photon extraction efficiency and the mean photon path length was investigated, and an appropriate height of the active region was proposed. In a typical LED, as the absorption of the electrode increases, the photon extraction efficiency decreases from 18% to 15% and 13%, and the photon extraction efficiency is highest when the height of the active area is located in the center between the two electrodes. In the tilted LED, as the absorption of the electrode increases, the photon extraction efficiency decreases from 38% to 33% and 25%, and the photon extraction efficiency is highest when the height of the active area is located in the center between the two electrodes. The tilted LED can increase the photon extraction efficiency more than twice than that of a typical LED, where photons are trapped inside the chip due to total reflection.

• Journal of Power Electronics
• /
• v.16 no.2
• /
• pp.815-822
• /
• 2016

The efficiency of light-emitting diode (LED) devices is a significant factor that reflects the capability of these devices to convert electrical power into optical power. In this study, a method for estimating the efficiency of LED devices is proposed. An efficiency model and a heat power model are established as convenient tools for LED performance evaluation. Such models can aid in the design of LED drivers and in the reliability evaluation of LED devices. The proposed estimation method for the efficiency and heat power of LED devices is verified by experimentally testing two types of commercial LED devices.

• Journal of the Optical Society of Korea
• /
• v.17 no.1
• /
• pp.22-26
• /
• 2013

The author analyzes the luminous efficiency of the phosphor-conversion white light-emitting diode (LED) that consists of a blue LED chip and a yellow phosphor. A theoretical model is derived to find the relation between luminous efficiency (LE) of a white LED, wall-plug efficiency (WPE) of a blue LED chip, and the phosphor absorption ratio of blue light. The presented model enables to obtain the theoretical limit of LE and the lower bound of WPE. When the efficiency model is applied to the measured results of a phosphor-conversion white LED, the limit theoretical value of LE is obtained to be 261 lm/W. In addition, for LE of 88 lm/W at 350 mA, the lower bound of WPE in the blue LED chip is found to be ~34%. The phosphor absorption ratio of blue light was found to have an important role in optimizing the luminous efficiency and colorimetric properties of phosphor-conversion white LEDs.

• Proceedings of the Materials Research Society of Korea Conference
• /
• 2003.11a
• /
• pp.21-21
• /
• 2003

To increase the light-emission efficiency of LED, we increased the internal and external quantum efficiency by suppressing the defect formation in the quantum well and by increasing the light extraction efficiency in LED, respectively. First, the internal quantum efficiency was improved by investigating the effect of a low temperature (LT) grown p-GaN layer on the In$\sub$0.25/GaN/GaN MQW in green LED. The properties of p-GaN was optimized at a low growth temperature of 900oC. A green LED using the optimized LT p-type GaN clearly showed the elimination of blue-shift which is originated by the MQW damage due to the high temperature growth process. This result was attributed to the suppression of indium inter-diffusion in MQW layer as evidenced by XRD and HR-TEM analysis. Secondly, we improved the light-extraction efficiency of LED. In spite of high internal quantum efficiency of GaN-based LED, the external quantum efficiency is still low due to the total internal reflection of the light at the semiconductor-air interface. To improve the probability of escaping the photons outside from the LED structure, we fabricated nano-sized cavities on a p-GaN surface utilizing Pt self-assembled metal clusters as an etch mask. Electroluminescence measurement showed that the relative optical output power was increased up to 80% compared to that of LED without nano-sized cavities. I-V measurement also showed that the electrical performance was improved. The enhanced LED performance was attributed to the enhancement of light escaping probability and the decrease of resistance due to the increase in contact area.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.16 no.3
• /
• pp.109-113
• /
• 2016

In this paper, we propose efficient LED lighting control algorithm using a David star magic square. Such algorithms increases the power reduction, the heat efficiency and LED life cycle and the efficiency of the LED lighting control consumption. Lighting system using existing Magic square algorithm could be reduced to increase the heat efficiency of the LED because the LED lighting time of the reduced cross-lighting. but it has a limit to the lighting control. If should apply the this proposed algorithm, can reduces power consumption and increases LED life-cycle, heat efficiency of LED lighting module and efficiency of the lighting control of the LED. This paper proposed that algorithm is by using a David star magic square on the LED Matrix. Divided into twelve areas to move the pattern in constant time interval, to perform the cross rotation and inversion techniques to thereby light up. In this paper proposed algorithm of this paper was compared with existing Magic square approach. As a result, power consumption and heat-value and luminous flux was reduced as the conventional lighting system. And, the LED lighting control increase the efficiency.

• Journal of the Optical Society of Korea
• /
• v.19 no.3
• /
• pp.311-316
• /
• 2015

We investigate the temperature dependence of the phosphor conversion efficiency (PCE) of the phosphor material used in a white light-emitting diode (LED) consisting of a blue LED chip and yellow phosphor. The temperature dependence of the wall-plug efficiency (WPE) of the blue LED chip and the PCE of phosphor are separately determined by analyzing the measured spectrum of the white LED sample. As the ambient temperature increases from 20 to $80^{\circ}C$, WPE and PCE decrease by about 4.5% and 6%, respectively, which means that the contribution of the phosphor to the thermal characteristics of white LEDs can be more important than that of the blue LED chip. When PCE is decomposed into the Stokes-shift efficiency and the phosphor quantum efficiency (QE), it is found that the Stokes-shift efficiency is only weakly dependent on temperature, while the QE decreases rapidly with temperature. From 20 to $80^{\circ}C$ the phosphor QE decreases by about 7% while the Stokes-shift efficiency changes by less than 1%.

• Journal of Biosystems Engineering
• /
• v.38 no.4
• /
• pp.279-286
• /
• 2013

Purpose: This study was conducted to analyze the utilization efficiencies of electric energy and photosynthetically active radiation of lettuce grown under red LED, blue LED and fluorescent lamps with different photoperiods. Methods: Red LED with peak wavelength of 660 nm and blue LED with peak wavelength of 450 nm were used to analyze the effect of three levels of photoperiod (12/12 h, 16/8 h, 20/4 h) of LED illumination on light utilization efficiency of lettuce grown hydroponically in a closed plant production system (CPPS). Cool-white fluorescent lamps (FL) were used as the control. Photosynthetic photon flux, air temperature and relative humidity in CPPS were maintained at 230 ${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, $22/18^{\circ}C$ (light/darkness), and 70%, respectively. Electric conductivity and pH were controlled at 1.5-1.8 $dS{\cdot}m^{-1}$ and 5.5-6.0, respectively. The light utilization efficiency based on the chemical energy converted by photosynthesis, the accumulated electric energy consumed by artificial lighting sources, and the accumulated photosynthetically active radiation illuminated from artificial lighting sources were calculated. Results: As compared to the control, we found that the accumulated electric energy consumption decreased by 75.6% for red LED and by 70.7% for blue LED. The accumulated photosynthetically active radiation illuminated from red LED and blue LED decreased by 43.8% and 33.5%, respectively, compared with the control. The electric energy utilization efficiency (EEUE) of lettuce at growth stage 2 was 1.29-2.06% for red LED, 0.76-1.53% for blue LED, and 0.25-0.41% for FL. The photosynthetically active radiation utilization efficiency (PARUE) of lettuce was 6.25-9.95% for red LED, 3.75-7.49% for blue LED, and 2.77-4.62% for FL. EEUE and PARUE significantly increased with the increasing light period. Conclusions: From these results, illumination time of 16-20 h in a day was proposed to improve the light utilization efficiency of lettuce grown in a plant factory.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.44 no.4
• /
• pp.91-96
• /
• 2007

The light extraction efficiency in GaN-on-sapphire LEDs based on a simple model was analyzed qualitatively. The light extraction efficiency in the LEDs is simulated numerically by using ray tracing method. In the present study, the extraction efficiency was simulated on flat LED and PSS(patterned sapphire substrate) LED. The role of the patterned sapphire substrate in PSS LED are analyzed and discussed. And, the effects of reflectance on flat LED and PSS LED were investigated. This analysis of simulation results provide a numeric figure for the extraction efficiency of LEDs and are helpful in the design of high brightness GaN LEDs.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.27 no.9
• /
• pp.15-22
• /
• 2013

A new LED lamp driving technology with a charge pump instead of a conventional DC-DC converter is proposed. The proposed driving technology is used to control the LED lamp with digital dimming. The power loss in the zener diodes is reduced because the charging process of the capacitors is selectively controlled according to the digital control signal. From the experimental results, when dimming four LED lamps simultaneously, the average driving circuit efficiency of 89% is obtained, regardless of the dimming level. White light with color temperature over a range of 2800~7200K was produced by dimming control of red, green, blue and amber LED lamps with the proposed driving circuit. The characteristics of the driving circuits can be changed depending on the characteristics of the R, G, B, and A LED lamps. The efficiency of the driving circuits up to a maximum 89% can also be obtained depending on the combination of LED lamps. The driving technology with digital dimming control for LED lamps proposed in this paper would be effective for obtaining high efficiency in LED driving circuits and remote control of LED lamps using digital communications.