National foreword

This Published Document is the UK implementation of ISO/TR 9241‑313:2025.

The UK participation in its preparation was entrusted to Technical Committee PH/9, Applied ergonomics.

A list of organizations represented on this committee can be obtained on request to its committee manager.

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This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

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This publication is not intended to constitute a contract. Users are responsible for its correct application.

This publication is not to be regarded as a British Standard.

Compliance with a Published Document cannot confer immunity from legal obligations.

This Published Document was published under the authority of the Standards Policy and Strategy Committee on 31 July 2025.

Foreword

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This document was prepared by Technical Committee ISO/TC 159, Ergonomics, Subcommittee SC 04, Ergonomics of human-system interaction.

A list of all parts in the ISO 9241 series can be found on the ISO website.

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Introduction

This document provides an overview of recent research on applying the optical reflection measurement methodology for flat direct view electronic displays to electrophoretic displays (EPDs). This document contributes background to ISO 9241‑307, ISO 9241‑305 and ISO 9241‑303, providing information regarding reflective displays in ambient indoor and outdoor illumination environments defined by CIE 015:2018, CIE S017:2020, and ISO/CIE 11664-2:2022.

Reflective displays convey information by modulating the reflected light, using independently controlled segments or pixels. Any reflective display performs the following two basic optical functions, either equally for all wavelengths achromatically or for selective wavelengths chromatically:

— reflecting ambient illumination towards the human observer;

—modulating the amount and spectral distribution of the reflected light.

For example, EPDs use electrically charged pigments to reflect and modulate light. Opaque white pigments with near-Lambertian reflection characteristics form the paper-like, diffuse reflecting background. Light-absorbing black pigments attenuate the reflected light as traditional ink does on paper. These properties differentiate EPDs from other display technologies by its paper-like appearance that offers a wide range of viewing directions and sunlight readability. Other properties are low power consumption and the absence of flicker. Other known reflective display technologies use reflectors with metallic, mirror or retroreflective characteristics, combined with diffusers, achromatic reflection modulators (for example liquid crystal shutters) and a colour filter array (CFA). EPDs are used in static and mobile applications including e-readers, wearables and signage for both indoor and outdoor applications.

A reflective display must have ambient illumination for the displayed information to be visible. Ambient illumination has directional and diffuse components. In outdoor environments, direct sunlight is the directional component, and skylight the diffuse component. In indoor environments, the diffuse component is dominant, e.g. diffuse daylight through windows and light is scattered by walls and ceiling. In addition, specular reflection of light sources of various sizes (from small luminaires to large windows) has the potential to obliterate the information on display screens. This document explains how to separately measure the display’s reflection characteristics under specific measurement illumination conditions, e.g. off-specular directional, hemispherical-diffuse, and specular variable aperture source (VAS) illumination. The three fundamental reflection components (specular, haze, and Lambertian) are measured separately and as a function of illumination source size. Once the reflection coefficients for each illumination geometry are measured, the reflected luminance from each illumination component is determined, and the infinite variety of ambient multi-source illumination is expressed as a summation of reflected illumination components from these sources. The total spectral radiance entering the observer’s eye when viewing a display is then predicted as a summation of all the ambient light components reflected into the direction of viewing. The contributions from each source are scaled according to their irradiance spectra for specific in- and outdoor illumination environments.

This document includes examples of standardized indoor and outdoor illumination conditions, and uses EPDs to illustrate the measurement methods.

1 Scope

This document provides background information and a validated methodology for optical reflection measurements for flat direct view electronic displays. This document includes calculation methods for using measured reflection coefficients to predict display performance in specific indoor and outdoor ambient illumination conditions.

This document demonstrates optical measurements of electrophoretic displays (EPDs), as a reflective electronic visual display technology; many methods are also applicable to other appropriate reflective and emissive displays. This document does not include a methodology for ergonomics evaluation.

2 Normative references

3 Terms, definitions and abbreviated terms

3.1 Terms and definitions

3.2 Abbreviated terms

4 Reflective display technology

5 General optical measurement methodology

5.1 Spectral radiance of display in ambient illumination

5.2 General concept of ambient illumination

5.3 Theory of reflected spectral radiance of display in ambient illumination

5.4 Components of spectral radiance reflected by the display

6 Measurement methods for display reflection

6.1 General

6.2 Definitions and symbols

6.3 Calibration standards and measurement samples

6.4 Measurement methods and examples of bi-directional reflection distribution function (BRDF)

6.5 Measuring specular reflectance under illumination from a variable aperture source

6.6 Measuring off-specular reflectance under directional illumination

6.7 Measuring reflectance under hemispherical-diffuse illumination

6.8 Measuring reflectance under off-specular directional and hemispherical-diffuse illumination

7 Prediction of display contrast in ambient illumination

7.1 Components of reflected spectral radiance

7.2 Prediction of display contrast

8 Conclusions

Bibliography

PD ISO/TR 9241-313:2025

Ergonomics of human-system interaction - Optical measurement methods for reflective displays

Current

Published:

31 Jul 2025