Conferences and supporting programme
The race toward Rec2020 and HDRI – OLED vs. LC display technology
This paper presents measurement results for state-of-the-art OLED and LC-display screens characterizing the stability of chromaticity and luminance with respect to viewing direction and electrical driving. We also present data concerning the reflective properties of both display technologies as a basis for comparison of display performance under ambient illumination. The obstacles that have to be overcome for realization of Rec. 2020 and HDRI are introduced and discussed for both OLED and LC-displays. Summary Both ITU-R Recommendation BT.2020 (aka Rec. 2020 or BT.2020) as well as high-dynamic-range imaging (HDRI) both establish demanding challenges to the electronic display industry. The chromaticity gamut according to Rec. 2020 requires highly saturated primary spectral distributions (FWHM < 10nm) and HDRI demands luminance levels (depending on the specific realization) between 0.005 cd/m2 and 1,000/4,000 cd/m2. In the case of LCDs the color filters have to be optimized with respect to accurate and effective spectral separation in order to realize Rec. 2020 chromaticities with LED, laser or maybe quantum-dot (QG) illumination [1, 2, 3]. The spectral sharpening of QD or OLED emission which is required for the Rec. 2020 primaries reduces the luminous efficacy of the display and introduces chromaticity variations with viewing direction. In the case of high dynamic range imaging (HDRI) OLED displays offer attractive black states in dark or at least dim ambient situations as an intrinsic advantage of emissive displays, while the dark states of LCD screens have to be explicitly prepared by elaborate back-light units (BLUs) with local dimming. While the required high peak luminance levels can be provided by LCD-screens with local dimming BLUs, this feature is more difficult to realize with OLED emission, or at least at the expense of OLED lifetime. Special sub-pixel arrangements (e.g. RGBW) may be helpful to generate higher peak white levels. In order to assure good display performance in realistic application situations, i.e. outside the dark room, the reflectance of the displays has to be well controlled to avoid bleaching of colors and reduction of contrast by ambient light sources. In the case of OLED displays, reflections are often reduced by circular polarizers which however - if not properly designed - may introduce additional chromaticity variations with viewing direction. We present reflectance evaluations according to IEC 62341-6-2 with both hemispherical and directional illumination together with 2D reflectance distributions evaluated under point-source illumination.
--- Date: 28.02.2019 Time: 11:20 - 11:40 Location: Conference Counter NCC Ost