Since several years light emitting diodes are in use to generate white light. Pixels with green, red and blue LED's are arranged to get any coordinate in the CIE - diagram with matched current for each diode. For instance Siemens Opto Semiconductor (OS) now OSRAM Opto Semiconductor offers multi chip LED's (LHGB T676) especially for the application above. A far better solution for producing white light represents luminescence conversion. The emitted light of blue diodes is used as a primary source for exciting organic or inorganic fluorescent. By conversion, "Stokes Shift", red, green, yellow and mixed colored light can be generated. After first studies of Fraunhofer IAF Freiburg Siemens OS selected in cooperation with OSRAM an especially qualified converter, a yellow light emitting phosphor. This phosphor is used since several years for production of fluorescent lamps and can be produced in high quality. The fluorescent is distinguished by high thermic and chemical resistance. Very good spectral characteristics and quantum efficiency of nearly 100% are typical. By additive mixing of color the yellow radiation of the fluorescent and the incomplete absorbed blue light of the LED make the assembly of single-chip-white-LED's near the white color point possible. In established technology Siemens OS developed a casting resin which contains the fluorescent and his production procedure. Patents are taken out. This casting resin can be used in mass production for assembly of SMT-LED's. The start of ramp up was in 6/98. Further activities for development of fluorescent for different tendencies near the white color point. By changing doping material and use of new producing methods a shift to the red or green sector of CIE-diagram can be reached. This makes single-chip-white-LED's for common illumination possible. Additional advantages in stability of color and efficiency are to expect by luminescence of UV-light emitting diodes.
