Progress in Effects of Optical Thin-film on Light Extraction Efficiency of LED

LED has many advantages such as energy saving and environmental protection as a new generation of light.However,low light-extraction efficiency limits its popular applications in the illuminating field.Light-extraction efficiency is influenced by many factors including packaging materials,packaging structure,luminous efficiency of the phosphor,the transmittance of transparent conductor film and the reflectance of substrate.Development of optical thin-films in LED area was reviewed,moreover,the developing tendency of combinating optical thin-films with nano technology in the LEDs were prospected.Optical thin-films can be used in the LED structure to improve the light-extraction efficiency,such as using high anti-reflective films as the transparent conductor diffusion layer,using high reflective films as the reflector under the substrate,which can effectively reduce the influence due to the low light transmittance of transparent conductor and low reflectance of substrate.