35.1: Invited Paper: Measurement and Standardization of Display Lighting Units

Abstract

Display lighting unit has always been the focus for optimization when comes into display engineering to improve its electrical, optical, and electro‐optical performance. In recent years, with the development of reflective LCD (liquid crystal display), electronic paper display, laser projection display, etc., the measurement of display lighting unit has received more attention. The IEC TC110 "Electronic Display" established the standardization team PT62595 to develop international standards. Currently, the project team has worked a variety of lighting technologies, including back light unit (BLU) and front light unit (FLU), light module and engine, light bar, and light components. In this paper, we reviewed the roadmap of this group and key items that involve in the measurement methods to give an overview of the documents.In the previous year, the IEC released two new standards, IEC62595‐2‐2 “Measuring methods of LED light bars used in LCD BLUs” and IEC62595‐2‐3 “Electro‐optical measuring methods of LED frontlight unit”. Both documents have now been put into the implementation in the display industry.In IEC 6595‐2‐2, spatial luminance uniformity and angular luminance, color uniformity and color angular uniformity were addressed. In Figure 1, it shows an example of a typical light bar luminance distribution profile to indicate the luminance uniformity by quantifying the information along axis.Example of the luminance distribution profiles along the x‐axis, Lv(x, o)figureIn addition, in order to achieve these characteristics, the optical coupling analysis and optimization between the light bar and the light guide plate (LGP) was discussed. Furthermore, this work introduced the specifications on the requirements for test environment, the architecture of the test equipment, the reference diffuser settings, and the coordinate system.In IEC 62595‐2‐3, the standard specifies the measurement conditions and measuring methods for determining electrical, optical, and electro‐optical properties of LED FLUs for reflective displays. In FLU, the light ray of the FLU with a reflective LC display can be sensitive to the testing position and viewing direction. As shown in Figure 2, light rays are introduced to the LGP (light guide plate) from the coupling side. The rays are reflected on the inner surfaces of the micro‐structures (on the front surface) due to TIR (total internal reflection). The FLU is served as a transparent medium that has reflection property on both surfaces. We explained some of the factors that were covered in the standard document for the measurement and evaluation of both surfaces, including angular luminance distribution, luminance uniformity, spectral power distribution, chromaticity uniformity and angular color uniformity in CIE 1976 system, as well as FLU‐polarization characteristics and optical noise (undesired luminance) along the zenith angle in any azimuth angle.Light rays of FLU with a reflective LC displayfigure