The use of white or color tunable LEDs (light-emitting diodes), which can replace a large light source apparatus and
light-guiding fiber bundle, enable the miniaturization of the whole endoscope system and remove constraints on the
design of its shape. We have developed a novel white LED for a new experimental prototype LED-illuminated gastrointestinal endoscope
having the color rendering in the clinically important red range at around 600 nm.
A near-ultraviolet (UV)-based white light-emitting diode (LED) lighting system linked with a semiconductor InGaN LED and compound phosphors for general lighting applications is proposed. We have developed for the first time a novel type of high-color rendering index (Ra) white LED light source, which is composed of near-UV LED and multiphosphor materials showing orange (O), yellow (Y), green (G), and blue (B) emissions. The white LED shows the superior characteristics of luminous efficacy and high Ra to be about 40 lm/W and 93, respectively. Luminous and chromaticity characteristics, and their spectral distribution of the present white LED can be evaluated using the multipoint LED light source theory. It is revealed that the OYGB white LED can provide better irradiance properties than that of conventional white LEDs. Near-UV white LED technologies, in conjunction with phosphor blends, can offer superior color uniformity, high Ra, and excellent light quality. Consequently we are carrying out a "white LEDs for medical applications" program in the second phase of this national project from 2004 to 2009.
We have performed theoretical studies on the luminous characeristics of white LED light source which composed of multi phosphors and near ultraviolet (UV) LED for general lighting. White LED source for general lighting applications requires the conditions that have high-flux, high luminous efficacy of radiation (> 100 lm/W) in addition to high color rendering index (Ra > 90) and variable color temperatures. Recently, we have proposed a novel type white LED based on multi phosphors and near UV LED system in order to high-Ra (>93). We will describe the excellent luminescence properties of white LED consisting of orange (O), yellow (Y), green (G) and blue (B) phosphor materials, and near UV LED. The color spectral contributions of individual phosphor-coated LED are theoretically analyzed using our multi LED lighting theory calculated the maximum luminous efficacy can be estimated to be approximately 300 lm/W having a high Ra of about 90 taking into account individual radiation spectrum. Illuminance distribution of white LED is in fairly good agreement with the experimental data.
KEYWORDS: Light emitting diodes, LED lighting, Lamps, Light sources and illumination, Solar cells, Sensors, Light sources, Light, Photovoltaics, Control systems
We describe the lighting characteristics and systems of the power energy-saving type street lamp which consists of white light-emitting diodes (LEDs), and a solar-cell and battery system. The prototype street lamp has been constructed by two LED light sources, each of which includes a total of 700 units of 10 cd-class white LEDs. The white LED lighting system is mainly divided into three components which are the control, the electric-power supply and LED lighting divisions. The illuminance is normally 80 lx. When a person approaches within 2 m near the lamp, the body sensor catches the situation. The illuminance then increases to about 660 lx, which is about 50 times brighter than that of a white incandescent lamp. The color rendering index is estimated to be 85 which is similar to that of three color fluorescent tube. The illuminance distribution can be analyzed by our recently developed 'multi sources of LED light' theory.
The basic illumination characteristics of an efficient white LEDs lighting source, which is composed of cannon-ball type 10 cd-class InGaN-based white LEDs, are described. It is noted that the temperature and forward-bias current dependence under full wave rectification of AC 100 V gives a significant effect to both electroluminescence properties and luminous efficacy. We have obtained a maximum luminous intensity of 95000 cd/m2 and a luminous efficacy of about 27 lm/W at an electric power of 20 W (at a constant current of 10 mA). The developed white LEDs lighting source indicates two injection electroluminescence peaks at 465 and 555 nm, which are originated from a blue LED and a YAG:Ce3+ phosphor, respectively. The illuminance distribution of the LED lighting source was analyzed using our `multi sources of LED light' theory. We have performed the design of a street lighting as the practical application using the 700 LEDs array lighting source.
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