Creating Accessible Images
Graphics that Cause Seizures
Article Contents
- Page 1: Images Introduction
- Page 2: Images that Enhance Comprehension
- Page 3: Color and Contrast
- Page 4: Text Within Graphics
- Current page: Page 5: Graphics That Cause Seizures
- Page 6: Creating Effective Alternative (
alt) Text - Page 7: Long Descriptions
Flicker and Strobe
The main point of this resource can be summarized very succinctly:
Important
Visual effects that flicker or produce a strobe-like effect may cause seizures in some individuals.
Seizures induced by flickering or strobe-like effects are known as photoepileptic seizures. Seizures can be dangerous. Don't be responsible for causing them.
How Can You Know If Your Graphics Will Cause a Seizure?
There is no absolute threshold at which a harmless animation turns into a dangerous, seizure-causing graphic. However, the guidelines that are used in the United States under Section 508 have set the threshold between 2 and 55 flickers per second. This does not mean that anything that moves at that rate will cause a seizure, because that would make all videos and animations unusable. Movement is not the issue. Flickering and strobe-like effects are the issue.
Example
Warning
The following examples are BAD examples! Do not follow these links if you think you might be susceptible to photoepileptic seizures.
- A strobing, flickering image
- An optical illusion image (the lines appear to be in motion)
Most designers don't create graphics that even approach the point that they might cause seizures, but some multimedia developers do venture into this territory. Flash designers are especially notorious for creating modernistic animations that flicker and strobe across the screen. Be careful when you design your animations. Don't cause a seizure.
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