Seen from the relatively light intensity distribution curve of LED chip, the radiation of the platform irradiance p-n junction belongs to Lambertian type, namely the beam intensity changes with the cosine of the emergence angle. It is reasonable to simplify p-n junction to point light. It is reliable to calculate the light intensity by using Fresnel transmissivity formula, the chip relatively light intensity distribution curve and this kind of light intensity calculation method will be the basis of studying the complicated packaging structure.
Seen from figure 6, when neglecting the light absorption of the packaging materials, the output efficiency of LED with hemispherical packaging will amplify with the growth of the refractive index of the packaging materials. However, the refractive index of the present epoxy resin packaging materials is always in 1.4-1.6, the change is limited; therefore, we should look for the new packaging materials through other methods to improve the light output efficiency of LED.
The cylinder height has a certain influence on LED efficiency, the higher the cylinder is, the side area is larger, the light loss is more, which will cause the decline o the overall efficiency. Usually, in order to decrease the light loss of the side face, we put a reflection cup behind the chip; therefore, the influence of the cylinder height is relatively small, which is our next study subject.
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