When white LED operating, the highest ideal effectiveness is η=39.5%. But phosphors and window materials absorption is far more than 5% analysis hypothesis, when analysis，it isn’t included the loss of carrier impurities and defects in the chip, internal quantum efficiency and the extraction yield were estimated on the high side. Especially under operating state, chip temperature rise causes blocking layer resistance and pressure drop decline and the carrier energy decline and loss increasing, make the internal quantum efficiency of the chip and quantum withdrawal rate drop, as a result，output spectrum red shift, the range decline. And blue light red shift will also cause phosphors stimulate efficiency drop and the increase of the absorption, thereby further increase the LED efficiency decline. At present, the actual efficiency of white LED about between 20% ~ 20%.
Considering various factors, the result shows that the actual energy efficiency of white LED and mercury vapor discharge fluorescent lamps are broadly similar, LED luminous efficiency also won’t significantly higher than T5 fluorescent.
Still calculate according to the highest energy efficiency (39.5%), as mentioned above, if the 1/4 blue spectral remains the same, the other 3/4 convert into the center wavelength is 540nm yellow light is the best spectral ratio to obtain high photosynthetic efficiency white light. Blue spectral band center wavelength’s visibility function is 0.038; the output blue light spectrum to the luminous flux’s contribution is 2.56 lm. Yellow band’s center wavelength is 540 nm, visibility function is 0.954, and the contribution of Yellow light to luminous flux is 193.03lm. Therefore the highest ideal energy efficiency of white LED is 196lm/w. Actual light efficiency will be lower, of course, in addition to the spectrum color rendering index increase to 80 above, white LED light efficient will also decline.