A lot people need a white light source when Development of LED project. Development of white LED in 1998. This LED is made by a GaN chip and yttrium aluminum garnet (YAG) package together. GaN chip as blue (p=465nm, Wd=30nm) lightl, high temperature sintering made of YAG containing Ce3+ phosphor emitting yellow light emission  by this blue light, peak 550nm.Blue LED substrate is mounted in the reflective cavity bowl, covered with a thin layer of resin mixed with YAG, about 200-500nm. The blue part of the LED substrate is absorbed by the phosphor,and the other part is mixed with the yellow light can geted white.adjust the thickness of the phosphor layer and changing the YAG phosphor chemical composition of the phosphor layer can the 3500 – 10000 K color temperature colored white.  Import thing is the medium that between the two poles of the light-emitting diode, powder, and called the phosphor, different media emit different colors of light.