LED lighting has higher luminous efficiency and longer life; it does not contain harmful substances mercury; its service life is almost independent of the number of times the lamp is switched, and it can promote “turn off the lightsâ€; it can be instantly brightened and other outstanding advantages, and is considered to eventually replace incandescent Lamps and energy-saving lamps have become the mainstream of energy-saving lighting. In fact, only when the cost performance of LED lamps exceeds that of incandescent lamps, especially more than the currently widely used energy-saving lamps, can it become the mainstream of general-purpose lamps.
The subject of LED lighting seems to be very clear, that is, the light efficiency needs to be greatly improved under the premise of ensuring the light quality, for example, more than double the energy-saving lamp; the price needs to be greatly reduced, preferably close to the energy-saving lamp; Energy saving lamp.
Most of the current LED general illumination lamps are composed of a power LED plus a metal heat sink and a constant current driving circuit. The bulky metal radiator not only increases the cost and weight of the lamp, but also consumes a lot of aluminum resources and is environmentally friendly. An LED light is like a metal ball, which is not conducive to safety, especially high-power LED lights. Therefore, many consumers still choose energy-saving lamps when they purchase.
This article will introduce a high-photon extraction rate, high efficiency, metal-free radiator LED general illumination lamp with LED 4Ï€ light output in combination with the research and development work of the company where the author is located (LED lighting lamp that can directly replace incandescent lamps and fluorescent flux lamps with considerable luminous flux) )technology.
The LED universal illumination lamp has more than double the luminous efficiency of the fluorescent energy-saving lamp; the color rendering index can be as high as 96; the LED universal illumination lamp with luminous flux of tens to 1600 lm and higher luminous flux can be manufactured, and the L70 can have a lifetime of up to 30,000. hour. It can directly replace incandescent lamps with 10 to 100W and higher power and fluorescent energy-saving lamps with considerable luminous flux.
First, LED chip 4Ï€ light, improve PN junction light extraction rate and actual light efficiency
The energy efficiency η of the white LED illumination process is:
η = ηI × ηO × ηC × K
Where ηI : internal quantum efficiency; ηO: external quantum efficiency; ηC: photon down conversion loss; K: luminescent powder absorption.
It has been analyzed that, under ideal conditions, ηI = 0.95; ηO = 0.5; ηC = 0.875; K = 0.95, therefore, the highest ideal energy efficiency η = 39.5%. Here, the external quantum efficiency ηO refers to the result that photons are absorbed by chips, window materials, phosphors, lenses, etc., or reflected at the interface of different refractive index media, and then absorbed, etc., that is, light of LED elements. Extraction rate. If the optical power equivalent of 3500K warm white light is calculated as 320 lm/W, the highest luminous efficiency is 320×0.395=126 lm/W. This is obviously underestimated. But from this we can see that an important and significant potential factor for improving LED efficacy is to increase the light extraction rate.
The light of the LED comes from the PN junction of the LED chip, and its illumination is originally a natural light uniformly emitted from the 4π solid angle, but almost all LED components are currently ≤ 2π light.
LED applications range from initial indicators to digital displays and current color large-screen displays, backlit displays for liquid crystal displays, etc. In these applications, it is necessary to focus the light that was originally emitted by 4π with a reflective bowl and lens, The light that is converted to ≤ 2π, including in-line, straw hat, surface mount (SMD), and COB; such transformations are needed and correct for these applications.
However, such a transformation causes the chip to emit light that is originally emitted backwards, which will significantly reduce the extraction rate of light emitted by the PN junction, that is, reduce the actual effective light efficiency of the LED, which is not necessarily required for LEDs with ≤ 2π light output. Lighting is not required. If the LED chip 4π emits light, the extraction rate of photons generated by the LED PN junction can be significantly improved, that is, the actual light effect of the LED can be improved.
FIG. 1 is a schematic diagram of light emission of an SMD type LED which is currently widely used. The LED chip is mounted at the bottom of the light reflecting bowl, and the reflecting bowl has a transparent medium whose light exit surface is a flat surface or a curved surface (an example of a plane in Fig. 1).
A portion of the 2π solid angle light (indicated in blue) emitted by the chip PN junction can be directly emitted from the light exit window, and the other portion of the light is totally reflected by the surface of the transparent medium and then reflected by the reflective bowl or directly reflected by the reflective bowl. Among them, the direct outgoing light is about 2π[1-cos(sin-1(1/1.5)]/2π=25%, here we set the refractive index of the transparent medium to 1.5, and the light emitted by the reflective bowl is 75%. The reflectance of the reflective bowl is 0.75. If the reflection of the reflective bowl and the absorption loss of the transparent medium are not counted, the total light extraction rate is (25 + 75 × 0.75)% = 81%.
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