Red strobe light.

Section 508: Flashing provision

One provision in the Section 508/255 refresh is to prevent flashing in patterns that may cause some people with photosensitive epilepsy to have a seizure. It is in the chapter that applies to hardware. The proposed provision states:

405.1 General. Where ICT emits lights in flashes, there shall be no more than three flashes in any one-second period.
EXCEPTION: Flashes that do not exceed the general flash and red flash thresholds defined in WCAG 2.0 (incorporated by reference in Chapter 1) are not required to conform to 405.

The main problem with this provision is that it is too strict. The WCAG 2.0 provisions do not have any guidance for hardware with flashing lights that do not occur on a screen (e.g., indicator LEDs). Strictly interpreted, the provision would apply to all indicator lights, including those that flicker to indicate network, data, or sound activity. Such indicator lights  would not be allowed to flash more than three times in a one-second timeframe.

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It important to keep this provision; otherwise, there would be no limitations to the frequency or flashing pattern of lights that might be used to alert or warn users. This could lead to triggering a seizures. However, it would be good to add an exception for some types of indication lights.

Categories of Hardware Lights

Lights on hardware may fall into different categories, including:

  1. Illumination
  2. Warning & Alerting
  3. Indicators of status
  4. Indicators of real-time activity

The flashing pattern and frequency of lights in the first three categories can be arbitrarily chosen, so they can easily meet 405.1 as it is currently worded. Even very bright lights that might be used to get somebody’s attention in warning or alerting circumstances can be flashed in patterns that meet the provision.

The problem is with the fourth category: lights that indicate real-time activity, such as lights that indicate network activity, hard drive IO, and LED VU meters and clipping lights on some sound equipment. The pattern or frequency of flashing may occur more than three times in a one-second timeframe, but the pattern cannot be changed without changing the entire nature of the lights and their purpose.

In typical products, the lights that indicate real-time activity are neither large nor very bright. Having large (in visual area) real-time activity lights would be the worst case since the trigger brightness thresholds for areas is relatively low, so these “large” indicators should not be exempted from the provision. Because of the danger to people with photosensitive epilepsy, and the difficulty calculating seizure thresholds in these circumstances, manufacturers should avoid having large flashing indicators of real-time activity.

Point light sources can be made to be potentially very bright in such a way that they may cause disability glare in the eyes of viewers that may make flash seem much larger than the actual point source. However, from a practical standpoint, such indicators of real-time activity are not typically that bright because they are annoying and potentially painful to all users. Because of the practical consideration, it seems reasonable that a narrow exception can be made to provision 405.1 for point-source lights that indicate real-time activity.

Recommendation

The recommended provision adds Exception 2.

405.1 General. Where ICT emits lights in flashes, there shall be no more than three flashes in any one-second period.
EXCEPTION 1: Flashes that do not exceed the general flash and red flash thresholds defined in WCAG 2.0 (incorporated by reference in Chapter 1) are not required to conform to 405.
EXCEPTION 2: Flickering of point light sources (where a point light source subtends no more than 1-degree of visual angle at the typical viewing distance) that indicate real-time activity (such as sound, hard drive, or network activity) are not required to conform to 405.


About J. Bern Jordan

Bern is a Ph.D. candidate and researcher in accessibility, usability, user interface, and technology interested in extending usability to all people, including people with disabilities and those who are aging. He currently works at the Trace R&D Center in Biomedical Engineering at the University of Wisconsin-Madison.

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