Flicker and Movement Standard v1.2
1. No-flicker requirement
1.1 You MUST NOT put any dynamic content which visibly or purposely flickers more than three times in any one second period onto a page.
1.2 If flicker is unavoidable, you MUST warn the user before they see the content (see section 2).
1.3 Where editorially appropriate, you SHOULD provide an alternative version of the content without the flicker which is as close to the original as is possible.
2. Flicker warning
2.1 For pages:
If you place a link to a page which flickers on your page, you MUST follow the link immediately with the following warning:
'Please note that this link takes you to a page which includes materials that flicker and so may not be suitable for users with photosensitive epilepsy.'
2.2 For games:
If your game includes content that flickers, you MUST place the following warning on the game's title screen (before the user is exposed to the flickering content):
'Please note that this game includes materials that flicker and so may not be suitable for users with photosensitive epilepsy.'
3. Definition of 'flicker'
Like the WAI Guidelines, these guidelines do not attempt to define what "flicker" is. Our current understanding is that moving content is not impacted by these requirements, but only moving content that "flickers" – quickly and continually switches between a light and dark colour, like a strobe light.
4. How to check your dynamic content
To check that your dynamic content does not flicker more than 3 times per second make a visual comparison of your content against the S&G Flicker Tool [
internal BBC site] – the W3C have no tool to offer.
5. Movement in general
5.1 You MUST NOT use blinking, flickering or flashing objects.
5.2 You MUST provide a mechanism to freeze any movement on the page UNLESS there is no alternative to the movement.
6. Reasoning & background
These requirements are based on WCAG 2.0 guidelines.
Individuals with photosensitive epilepsy can have seizures triggered by flickering or flashing in the 3 to 49 Hertz range(roughly equivalent to 3 to 49 flashes per second) with a peak sensitivity at 20 flashes per second.
Individuals with distractibility problems (e.g. some forms of Aspergers) may not be able to focus on page content with flicker or movement occurring in the same visual field.
Document history
| Date | Version | Change | Author |
|---|---|---|---|
| 21/09/10 | v1.2 | Addition of clause 5 on movement. Taken in from Accessibility guidelines v1.8. | Ed Lee |
| 28/05/10 | v1.1 | Edited and brought into line with WCAG 2.0 (W3C's accessibility panel) recommendations. | Ed Lee |
| 26/09/2003 | v1.00 | Standard renumbered as 1.00 on approval by Standards Exec | Jonathan Hassell |
| 23/07/2003 | v0.3 | After alterations required by Tech Forum to approve doc (on 22/07/2003 ) | Jonathan Hassell |
| 18/07/2003 | v0.2 | Second draft of the doc, with alterations required by Accessibility WG to approve it (see minutes of meeting on 09/07/2003 ) | Jonathan Hassell |
| 08/07/2003 | v0.1 | First draft of this doc, based on discussion at Accessibility WG meeting on 11/06/2003 | Jonathan Hassell |
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Like all other Future Media Standards & Guidelines, this page is updated on a regular basis, through the process described on About Standards & Guidelines.
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