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The actual energy efficiency and luminous efficiency of white LED(Part 1)

Any kinds of illuminants are bound to produce a variety of energy loss when convert electrical energy into light energy, conversion efficiency usually between 20% ~ 40%, it is difficult to achieve 50%. So basically can determine any light source, if the color rendering index is no lower than 80, the light will be no more than 140 lm/w. The only exception to this is: More than 150w power’s high quality ceramic metal halide lamp, when color rendering index is greater than 90, the true luminous efficiency can reach 130lm/w or slightly higher. If the ceramic metal halide lamp’s color rendering index decreased to 85, the light efficiency can reach 140 lm/w, its energy efficiency can reach 50% or slightly higher. Now more than 250w’s high pressure sodium lamp light efficiency although can reach to 1501m/w, but the color rendering index is under 27, its efficiency hasn’t yet reach 50% in practice. The total energy efficiency of mercury vapor discharge type fluorescent lamp is 20 ~ 35 %( depending on the lamp power, length and diameter), the corresponding luminous efficiency is about 55 ~ 100 lm/W, color rendering index is 80.

White LED is another type of fluorescent lamp. In terms of energy efficiency compare with mercury vapor discharge fluorescent lamp, the difference is: LED’s photon energy is only about 2.7eV blue-ray, 3/4 blue light photons after conversion, the total average quantum loss are only 12.6%. And the primary light of mercury vapor discharge fluorescent lamps is uv light, the photon energy is 4.86eV, it is much greater than the average photon energy of visible light, after convert into visible light quantum loss up to 54%, average quantum conversion efficiency is much lower than the LED; White LED light is limited angle lighting, quantum extraction yield less than 50%, and mercury vapor discharge fluorescent lamp is 4π solid angle all-round uniform glow, quantum extraction yield close to 100%;The emitted photons of white LED needs through different layers of refractive index of solid media absorption, reflection, refraction, and scatter. And mercury vapor discharge fluorescent lamps only has a thin layer of light transmittance of glass bulb shell, no other obstacles stand in the way of photon to escape, so the inside photon absorption of LED is much greater than mercury vapor discharge fluorescent lamp.

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