ISO 9241-391:2016

Overview

ISO 9241-391:2016 - part of the ISO 9241 series on ergonomics of human–system interaction - defines requirements, analysis and compliance test methods to reduce photosensitive seizures (PSS) caused by viewing image content on electronic displays. The standard applies to image contents (independent of device or environment) and targets protection of photosensitive individuals vulnerable to seizures triggered by flashing lights and certain regular patterns.

Key topics and requirements

• Image factors identified as provoking PSS:
  • Potentially harmful flashes (luminance/contrast changes, area of visual field, number of flashes per unit time, rapid sequence changes)
  • Red flashes (colour transitions to/from saturated red are especially provocative)
  • Regular patterns (discernible stripes, spatial frequency, motion vs. stationary, area occupied)
  • Cumulative risk (duration and repetition of provocative stimuli)
• Ergonomic requirements and recommendations focus on content design to reduce risk, including limits on flash characteristics, managing rapid scene changes, avoiding large-area saturated red changes, and controlling pattern properties and duration.
• Conformance and test methods: the standard specifies test procedures and a conformance process for assessing image content against the requirements, plus normative references (e.g., ISO 9241-302 terminology).
• Supporting annexes provide clinical context (Annex C), guidance on viewing environments (Annex D), details on saturated red (Annex E), and sample assessment procedures (Annex G).

Practical applications and users

ISO 9241-391 is useful for anyone creating, delivering or certifying visual content who must manage image safety and accessibility:

• Content creators and visual designers (film, TV, streaming, games, VR)
• UX/UI designers and web developers (video and interactive content)
• Broadcast and streaming platforms enforcing safety guidelines
• Display manufacturers and hardware test labs (validation of image playback)
• Accessibility specialists, health & safety officers, and regulatory compliance teams Practical uses include content review workflows, automated pre-publish testing, viewer warnings, production guidelines to avoid risky flashes or patterns, and conformance testing for safer distribution.

Related standards

• ISO 9241 series (human–system interaction ergonomics)
• ISO 9241-302 (terminology for electronic visual displays)
• ISO/IEC 40500:2012 (W3C WCAG 2.0) - web accessibility guidance
• ITU-R BT.1702 - broadcasting image safety considerations

Keywords: ISO 9241-391, photosensitive seizures, PSS, image safety, display content, conformance test methods, flashes, saturated red, regular patterns, accessibility.