Measurement Seminar – from SSL to DisplaysZurück
Englischer Online-Bericht von Arno Grabher-Meyer
Measurement is never a trivial task. The effort only makes sense if it is thoroughly executed with the appropriate equipment, well calibrated and adjusted. Otherwise, the results are not reproducible and therefore of questionable value. This is true for any measured parameter, but in light measurement especially, the effort, costs and requirements have become especially demanding. Measurement basics in regards to the measured parameters remain the same as before with conventional light sources, but this is not the whole story.
New quality criteria have to be documented that did not exist before or that were given constraints of the technology with minimal variation between competing brands. First, LEDs are directional light sources and any SSL design has to take this into account. Secondly, white LEDs emit a mix of light that is generated by the LED itself and some kind of color conversion material, which is at least slightly dislocated from the emission layer of the LED, having a completely different emission characteristic. In conjunction with other factors, this causes the spectral distribution to vary over emission angle. Third of all, not unique to LEDs but still relevant, the electronics to operate the LEDs, and here especially the digital character of the SSL system, have to be taken into account. By analogy, modern display technology also has some specialties that make measurement no trivial task.