If we use the hemisphere packaging, the light emitted from the chip will be perpendicular to the epoxy resin-air interface. According to the Fresnel refraction formula, when the normal incidence i1=i2=0, the photon transmissivity of p, s component are equal, n2, no respectively represent the epoxy resin and the refractive index of the air.
The refractive index of the epoxy resin is 1.5, the air refractive index is 1.0, and then we can calculate the photon epoxy resin-the transmissivity of the air interface. Because the photon intensity of p,s component emitted from p-n junction is assumed to be 1, then the total photon of any semi plane emitted by p-n junction is 180; For the emergent light, the angle interval is Δi2=1n , respectively summat the light intensity (Light Intensity Measurement With Goniophotometer) value Tp ,T under 0-90 degrees, then the result is the overflowing photon numbers of any semi plane of p,s components, make the two results divide 180, then get photon transmissivity of the chip-resin interface p,s components, the average value of the two results is the light output efficiency of the epoxy interface.
Change the refractive index of epoxy resin, get the value of the air refractive index and the chip refractive index at the interval of 0.1, respectively work out the light output efficiency of the chip-epoxy resin interface and the light output efficiency of the epoxy resin-air interface, multiply the two values and get the LED light output efficiency under different epoxy resin refractive conditions, the result is shown as figure 6
Figure 6 the light output efficiency changes by packaging materials refractive index
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