*This article is an English translation of a Japanese article.
Introduction
The “Three Flashes” rule in web accessibility is a crucial guideline designed to protect users, particularly those who are sensitive to light or at risk of photosensitive seizures (photosensitive epilepsy). Sudden flashes or strong visual changes can be dangerous for these individuals. Therefore, visual effects and videos used on websites or applications must be carefully controlled in terms of flash frequency and intensity. This article will explain the background of the “Three Flashes” rule and provide specific methods for implementing it.
What is the “Three Flashes” Rule?
The “Three Flashes” rule is a guideline designed to reduce health risks caused by visual stimuli. Specifically, if strong flashes or visual flickering occur more than three times in quick succession, it increases the risk of triggering photosensitive seizures, and thus, should be avoided. This rule is part of the international accessibility standard known as the Web Content Accessibility Guidelines (WCAG), specifically detailed under Guideline 2.3: Seizures and Physical Reactions.
Specific Requirements
According to WCAG 2.1, the following requirements are specified:
- No more than three flashes per second: Videos, animations, and even banner ads must not contain more than three flashes in one second.
- Limit flash intensity and area: Special care must be taken if flashes cover a large area of the screen or involve very bright, white flashes. This helps protect users sensitive to light.
Why is the “Three Flashes” Rule Important?
Photosensitive seizures are neurological reactions triggered by flashing lights or specific light patterns. These seizures are more common in younger individuals and those diagnosed with epilepsy. While commonly associated with television, video games, and movies, the same risks apply to content on the internet.
For example, flashing banner ads or videos with strong flash effects can pose this risk. Therefore, when designing websites and creating content, it’s essential to minimize the use of flashing lights.
How to Comply with the “Three Flashes” Rule
To follow the “Three Flashes” rule when creating web content or applications, the following practices are recommended:
1. Avoid or Limit Flashing Content
When producing videos or animations, it’s essential to avoid strong flashes or frequent light flickers. In action scenes or visually intense effects, aim to minimize flashing and create more subtle visual effects.
- Avoid flashing entirely: If possible, remove flashing effects or replace them with alternative visual effects.
- Reduce the frequency of flashes: If flashing effects are necessary, ensure that the flashes do not exceed three times per second, and reduce the frequency as much as possible.
2. Test Content Before Publication
Before publishing videos or animations on your website or application, always test the content to ensure it complies with flash frequency and intensity standards. Here are some effective testing methods:
- Use automated tools: Tools like the Photosensitive Epilepsy Analysis Tool (PEAT) can analyze content and evaluate the risk of triggering photosensitive seizures. These tools can automatically detect content with excessive flashing.
- Manual verification: Ideally, people at risk of photosensitive seizures should test the content. Team members should also visually check the content to ensure that no excessive flashing or flickering occurs.
3. Display Flash Warnings
If your content contains strong flashes, you should display a warning for users who may be sensitive to light. This allows users to avoid the content or prepare to view it in a safe environment.
- Example warning message:
“This content contains flashing lights or effects. If you have photosensitivity or epilepsy, please proceed with caution.”
4. Provide User Control Options
Another effective method is to offer users the option to disable flash effects or reduce the frequency of flashes. This is especially useful in games or interactive content, where allowing users to adjust visual effects provides a safer, more comfortable experience.
- Example: In the settings menu of a game, add an option to “Turn off flash effects.”
Conclusion
From a web accessibility standpoint, the “Three Flashes” rule is essential to reduce the risk of triggering photosensitive seizures. Sudden light flashes can pose significant health risks, so avoiding them in content creation is strongly recommended. By minimizing flashing content, conducting pre-release testing, and displaying warnings, you can create a safer and more inclusive web environment for all users.
Key Points
- Avoid more than three flashes per second: Limit the number of flash effects in your content to protect users sensitive to light.
- Conduct automated and manual testing: Use tools and visual checks to ensure your content complies with flash safety guidelines.
- Provide user controls for flash effects: Offer flexible options to accommodate all users by allowing them to disable or reduce flashing.
When creating web content, consider these strategies to build a safer and more inclusive digital experience for everyone.
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