Display Metrology and Light Measurement Standardization
June 4, 2015, Society for Information Display Symposium, San Jose, CA—Michael Becker from Instrument Systems reviewed the activities of CIE, IEC, and ISO on display standards. The rapid evolution of the displays is creating new challenges for the standards groups.
The three groups are working on the following topics: CIE Fundamentals of photometry and colorimetry Terminology (International Lighting Vocabulary), basics of light and color measurement (e.g. ISO 11664/CIE S014: Colorimetry) and characterization of the performance of light measurement devices (LMD, e.g. ISO/CIE 19476:2014).
IEC Data sheets for display components and devices The TC110 is currently consolidating the scattered measurement methods for LCDs and introducing methods for the measurement of speckle in laser display devices. Measurement methods for transparent displays (OLED and LCD) are under consideration as well as methods for measuring non-planar displays (e.g. cylindrical TV-screens, wearable conformable displays) and touch sensitive input devices.
ISO Ergonomics of human-system interaction The WG2 of the ISO/TC159/SC4 is currently revising and extending ISO 9241 part 305 with respect to standardized indoor and outdoor ambient illumination conditions, the corresponding measurement and modeling approaches, and measurement methods for reflective (ePaper) and transparent displays.
The CIE work is on developing a specific taxonomy and terminology. The International Lighting Vocabulary (ILV) is the reference for light and lighting terms and definitions. One area for change is the evaluation of the chromaticity of the light sources, displays, and surfaces. Array spectrometers are convenient but have variations in their bandpass functions and can be affected by stray light. CIE 214:2014 presents bandwidth corrections through an algorithm that compensates for line-spread with wavelength.
ISO/CIE 19476:2014 introduces performance quality indices and diagnostics for luminance meters (LMD). The standards addresses calibration uncertainties, spectral properties, UV and IR response, directional response, linearity, effect of temporal modulations, and effect of polarization of light. The working groups are extending the standard to the special case of imaging luminance measurement devices (iLMD) and to colorimetry.
CIE TC2-75 looks at curved and flexible sources. The work considers that a non-planar surface exhibits a change in chromaticity across its surface. Measurements require more attention be paid to the geometric details of the measurement setup and the conditions of the LMD. When laterally integrating LMD’s (“spot meters”) are used to measure a non-planar objects, the measurement field diameter should be much smaller than the local radius of curvature.
IED 62341-6-2 edition 2.0 details specifications of the illumination conditions for evaluating visual display performance. The standard specifies spectral distribution and levels of illumination for display testing. The intent is to provide environments that correspond to typical application situations. The measurement of transparent displays is under consideration. Measurements will have to include both on screen and through screen performance.
IEC TC110 is looking at laser speckle. The ability to use a laser projection system onto any surface opens up a wide range of applications. The problem is that speckle reduction techniques are required to make the designs comfortable to the viewer. Measurement and evaluation methods for laser speckle should be standardized soon.
ISO is working on ergonomics of human-system interaction with respect to ambient light reflections. The reflectometer setup comes from the previous work with CRTs. Newer technologies like anti-glare polarizers provide different reflections than the glass of a CRT, so the current issues are with haze, and not specular components. The difference may cause measurement uncertainties if the aperture angle is not well controlled. As a result, the standard group is considering the following changes: specification of illumination conditions for reproduction of indoor and outdoor scenarios, measurement of display reflectance and modeling methods for reflected radiance under arbitrary illumination conditions, measurement methods for transparent and reflective
Displays, measurement approaches (if needed) and precautions for non-planar displays, and measurement methods for “near-to-the-eye” displays.
