Optical measurement standards for reflective e‐paper to predict colors displayed in ambient illumination environments

• Published in: Color research and application Vol. 43; no. 6; pp. 907 - 921
• Main Author: Hertel, Dirk
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley & Sons, Inc 01.12.2018; Wiley Subscription Services, Inc
• Subjects: ambient color gamut; ambient contrast ratio; Bidirectional reflectance; Color measurement; Daylight; daylight readability; Diodes; Displays; Distribution functions; electronic paper; electrophoretic e‐paper; Emissivity; e‐paper; Illumination; Indoor environments; Lighting; measurement standards; Optical measurement; Radiance; Reflectance; Reflection; reflective display; Tablets
• ISSN: 0361-2317; 1520-6378
• DOI: 10.1002/col.22279

Color displays are viewed in ambient conditions ranging from indoor lighting to bright sunlight. For emissive displays such as phones or tablets, color and readability are disturbed by ambient light reflected from the screen. However, ambient light is required to view e‐paper, so color measurements must be reflection‐based. This article describes how a bidirectional reflectance distribution function‐based methodology for measuring the disturbing reflection on emissive displays has been applied to measure the useful reflection from e‐paper displays. These measurements have been embedded in recently developed optical measurement standards for e‐paper that contain color measurement specifications for spectral reflection and—if a front light is present—spectral radiance of each displayed color. Then the measurements are combined with ambient illumination models to predict how display colors would appear in realistic lighting conditions. Although developed for e‐paper, this concept can be applied to any type of color display. Examples illustrate the standard measurement methodology, and how to predict displayed colors on both handheld e‐paper and emissive displays in both indoor and daylight viewing conditions.