Lighting and display are two extremely important development areas in the photovoltaic industry today. The global fossil energy is increasingly exhausted, environmental pollution is becoming more and more serious, and white light that can meet the dual characteristics of “energy saving†and “environmental protection†at the same time. LED (Light emitting diode ), its application potential in lighting and display devices, has received a high degree of attention and attention in recent years.
White LEDs are considered to be the revolutionary light source for replacing hot and fluorescent lamps because of their dual characteristics of energy saving and environmental protection. Fluorescent materials are the key materials for lighting and display devices, especially since the development of high-brightness LEDs. Also highly valued. White LEDs have several feasible production methods. Among them, white LEDs made of phosphors have many advantages such as simple fabrication, easy driving, and low cost. In the future, lighting and display applications will inevitably play a role. A very important role.
There are currently three more common methods for making white LEDs. The first is to mix red, green, and blue light, and the third is to use ultraviolet light to emit light and then pass red, green, and blue fluorescence. Powder, while mixing white light; the third is to use blue light on the yellow phosphor, mixing white light. Most of today's high-brightness LEDs are made of semiconductor materials such as multi-phosphide (such as InGaAlP) or nitride (such as InGaN). The color of the light is limited by the light-emitting mechanism and the energy gap of the material. Wide monochromatic light. However, in terms of lighting and display applications, most of them need to use a white light source. If the LED is used to make a white light source, it is necessary to apply a combination of light and color to achieve the purpose of obtaining white light. Among the various feasible technologies for the combination of light and color of white LEDs, single-chip LEDs combined with various types of fluorescent materials for light color conversion and light mixing are the most convenient and cost-effective. The method, in which a white LED produced by using an inorganic phosphor (Phosphor), is generally also referred to as a PC-White-LED (Phosphor-modified white-LED).
In terms of LED (Blue-LED+Yellow phosphor), it is pointed out in the literature that in the emission spectrum of such white LEDs, the blue light band portion accounts for about 31% of the total white light energy, while the yellow light that is converted by the phosphor light occupies white light. A ratio of 69% of total light energy.
On the other hand, when a white LED (UV-LED+R/G/B phosphors or the like) produced by combining a phosphor with a UV-LED, all of the ultraviolet rays from the UV-LED are converted into visible light by conversion of the phosphor, and thus The light energy converted by phosphor is almost 100% of the total light energy of white light. According to the above analysis, the importance and status of phosphors in single-chip white LEDs can be clearly understood.
White LED
White LED was originally made of yellow light phosphor with blue LED and YAG (Ce3+; Yttrium Aluminum Garnet doped with Ce3+ activator). The launch of such white LED has attracted worldwide attention and has begun. A new era of LED applications. In fact, in addition to the aforementioned way of making blue LEDs and yellow phosphors, white LEDs can also be blue LEDs plus green/red or other combinations of phosphors, or UV-LEDs plus blue/green. /Red light or other combination of phosphors.
In addition, it is also possible to directly apply a plurality of LED chips of different light colors to form a single-chip white LED, or directly apply a plurality of LEDs of different light colors to form a white LED module or array. Although the driving circuit is relatively complicated and relatively high in cost, the color saturation or color gamut characteristic obtained in the display backlight is good [7], and the white light produced by combining the phosphor LEDs have different considerations in their applications.
In the application of LEDs, in addition to the aforementioned white LEDs, the color of light in the color gamut such as purple red and "unsaturated light" that cannot be obtained by a single LED chip, or the luminous efficiency of a single LED chip Poor light colors such as green and yellow light (a part of the light color in the 520-590 nm band) have application value. For light-emitting diodes made with phosphors, possible applications include lighting, backlighting, and pointing/decoration. As for the important characteristics that white LEDs must consider in lighting and display backlight applications, including: luminous efficacy, service life, color temperature, color rendering coefficient and color gamut/color saturation, etc., the internationally important features are currently actively Draft or develop relevant specifications and test standards. As for the important characteristics and requirements of white LEDs, they are described below.
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