Thread Subject: Re: FW: FLASH provisions.

Note

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From: Michele Budris
Date: Mon, Mar 17 2008 7:35 PM

Please be aware, this is asking for changes to 3J-Flashing that has
already been consensed, the addition of a new definitions for
"flash," "blinking," and divides the definition of "general flash and
red flash" into two definitions (one for hardware and one for
software/content).

The EWG is receiving many complaints about the amount of new material
being requested this late in the process.

Question for Gregg - who is this being submitted by? Was there a
subgroup that put this together or is it from you?

Michele


On Mar 17, 2008, at 5:00 PM, Gregg Vanderheiden wrote:

> Notes to TEITAC
>
>
>
> Here is the revised text for the FLASH provisions and their
> definitions. ALL aspects are included here for completeness.
>
>
>
> 1) this separates the hardware and software threshold
> definitions because hardware must be based on luminance while
> software/content is on ârelative luminanceâ (software and web pages
> control light given off but do not actually give off light.
>
> 2) This uses a similar function for hardware flashing as for
> software except that it has a factor for very high brightness LEDs
>
> 3) The hardware provision continues the simple âless than 3
> hzâ but also provides a way to meet it with flashing LEDs that do
> flash in provocative range.
>
> 4) Covers very bright LEDs but lets ordinary LEDs used for
> indicators etc pass.
>
> 5) removed 50 HZ from the SOFTWARE version since there is no
> line frequency reason to have content changing from frame to frame
> in a flashing manner. And 50% of people who are sensitive would
> be sensitive at 50 hz.
>
> 6) Keeps but restricts the hardware 50 and 60 hz exemption to
> products that need it due to use of line frequency but does not
> allow other frequencies in this range. It does allow flashing
> above 75hz which is the recommendation of Graham Harding.
>
> 7) Includes a provision #6 for products that auto âadjust for
> ambient light.
>
> 8) A number of other small fixes pointed out by people
>
>
>
> The âNOTES TO ACCESS BOARDâ are added to the Hardware Provision
> (and the same note to the Hardware thresholds) because we are
> unlikely to be able to reach consensus on the final equation for
> part #5 of the hardware provision (even though we want to include
> it since it provides considerable flexibility to industry in a way
> that preserves the protection level of the rest of our provision)
> in the time we have left. We want the information and provisions â
> but need more time to review them. Followup comments will need to
> be submitted by by interested parties.
>
>
>
>
>
> The hardware provision was designed to
>
> a) provide easy solutions that are more restrictive
>
> · any flash less than 3/sec
>
> · any flash that is dim
>
> · over 75hz
>
> · 50 or 60 hz if tied to line freq.
>
> b) then to provide more complicated but more flexible provision
>
>
>
> Included is the following NOTE that gives example of what would
> pass provision 5 â so that would make it easy to check these with
> your engineers and see if it would cause any problems.
>
>
>
> NOTE: Each of the following examples would meet option 5 (when
> viewed from at least 12 inches) even when all of the sources are
> flashing together at more than 3 Hz:
> 1 round LED with a diameter of 5 mm or less, and no more than
> 32,000 cd/m2.
> 1 rectangular indicator with a size of 10 by 20 mm or less, and no
> more than 2,100 cd/m2.
> 3 square indicators (within a 2.1 inch circle) each 6 mm square or
> less, and no more than 3,500 cd/m2
> 4 round indicators (within a 2.1 inch circle) each 8 mm in diameter
> or less, and no more than 1,400 cd/m2.
> 5 rectangular indicators (within a 2.1 inch circle) each 6 by 2 mm,
> and no more than 6,100 cd/m2.
> (For light sources that are Red flashes (that have a 590 nm
> wavelength or longer) the values for luminance in this note should
> be divided by 8.)
>
> (For comparison, the maximum brightness of a white screen on an LCD
> computer monitor is about 200 to 400 cd/m2)
>
>
>
> REMEMBER â manufacturers can use LEDs brighter than these as well
> (as long as they don't flash more than 3/sec. ) So you can have
> flashlights and strobe lightsâ¦.. Just not flashing more than 3 per
> second.
>
>
>
> Gregg
>
>
>
> BELOW IS THE PROPOSED LANGUAGE FOR THE DIFFERENT PROVISIONS AND
> DEFINITIONS.
>
>
>
> {NOTE TO TEITAC REVIEWERS. This mirrors software but uses a
> different threshold definition (and a qualifying âifâ phrase to
> facilitate elimination where it does not apply). Uses âeither â
> orâ language to make it clearer that there are two choices. May
> want to consider that in software provision}
>
> 2.1-B - Flashing (Hardware)
>
> If products emit light in [flashes] at any time then either there
> must be no more than 3 flashes in any 1 second period or the
> flashing must be below the general flash and red flash thresholds
> for hardware.
>
> NOTE ACCESS BOARD: the working group came up with the definitions
> for âgeneral flash and red flash thresholds for hardwareâ after
> much effort but there was NOT sufficient time to explore them as
> much as necessary to come to consensus on them. The âgeneral
> flash and red flash thresholds for hardwareâ therefore DOES NOT
> HAVE CONSENSUS. What the group did consense on were the following
>
> 1. very bright point sources or very bright small sources can
> be a problem (per Graham Harding)
>
> 2. Very bright point sources or very bright small sources
> should be allowed if they flash less than 3 per second
>
> 3. Flashing above 3 per second should be allowed if is as
> equivalently safe as with the Software flash thresholds.
>
> 4. Some metrics for identifying âequivalently safeâ were
> created but more time is needed by everyone to study them and their
> derivation before they are used by anyone including the Access Board.
>
> 5. The numbers were included in this report in order to
> facilitate review by different parties.
>
> There IS consensus on the flash provision for software and content
> and the general flash and red flash thresholds for software and
> content.
>
>
>
> 3-J - Flashing (Software/Content)
>
> Content or user interfaces must not contain anything that flashes
> more than 3 times in any one second period or the flashing must be
> below the general flash and red flash thresholds for content and
> user interfaces.
>
> {no change except to add âfor content and user interfacesâ at the
> end.}
>
>
>
> flash
> a pair of opposing changes in luminance (relative luminance for
> software and content) that can cause seizures in some people if it
> is large enough and in the right frequency range
> Note 1: See general flash threshold and red flash threshold
> definitions for information about types of flash that are not allowed.
> Note 2: See also blinking.
>
> {New â from WCAG. To clarify FLASH and BLINKING. Also needed for
> definitions of thresholds}
>
>
> blinking
> switch back and forth between two visual states in a way that is
> meant to draw attention
> Note: See also flash (It is possible for something to be large
> enough and blink brightly enough at the right frequency to be also
> classified as a flash).
>
>
> {New â from WCAG. To clarify FLASH and BLINKING.}
>
>
>
> {New â based off of software flash thresholds but considerably
> different to handle hardware issues.
>
> general flash and red flash thresholds for hardware
>
> a hardware flash is below the threshold (i.e. software or content
> passes) if any of the following is true:
>
> 1. there are no more than three General Flashes and / or no
> more than three Red Flashes within any one-second period; OR
>
> 2. the flash frequency is 50 or 60 Hz and is due to a refresh
> that is intrinsically tied to the local line frequency OR
>
> 3. the flash frequency is 75 hz or greater OR
>
> 4. general flashes (that have less than a 590 nm wavelength)
> are no more than 20 cd/m2
> AND red flashes (that have a 590 nm wavelength or longer) are no
> more than 2.5 cd/m2 OR
>
> 5. general flashes are no more than (1200/N0.3)(0.006/AREA â
> 1) cd/m2
> AND red flashes (that have a 590 nm wavelength or longer) are no
> more than (150/N0.3)(0.006/AREA â 1) cd/m2 OR
>
> 6. there is an adaptive brightness feature that always keeps
> the changes in luminance of flashes from all sources (that might
> flash > 3 hz) below the maximum of (1, ambient(in lux)/700 lux)
> times the threshold values in 4 or 5 above.
>
> - where N is the number of sources that are flashing
> together more than 3 times per second within a 0.024 steradian circle
> - where AREA is the summed area of the N sources,
> measured in steradians (at the minimum typical/expected viewing
> distance)
> - and where sources that are separated by less than .4
> degrees ( ~2mm at 12 inch viewing distance) are treated as a single
> source with AREA being the area from edge to edge of the group.
>
> NOTE: Most products can safely use a minimum typical / expected
> viewing distance of 12 inches where 0.006 steradians would be a
> circle of 1.05 inch diameter.
>
>
> NOTE: Red sources with wavelengths of 590 or more nm are especially
> provocative since, due to the way the eye and brain process light
> with longer wavelengths.
>
>
> NOTE: Each of the following examples would meet option 5 (when
> viewed from at least 12 inches) even when all of the sources are
> flashing together at more than 3 Hz:
> 1 round LED with a diameter of 5 mm or less, and no more than
> 32,000 cd/m2.
> 1 rectangular indicator with a size of 10 by 20 mm or less, and no
> more than 2,100 cd/m2.
> 3 square indicators (within a 2.1 inch circle) each 6 mm square or
> less, and no more than 3,500 cd/m2
> 4 round indicators (within a 2.1 inch circle) each 8 mm in diameter
> or less, and no more than 1,400 cd/m2.
> 5 rectangular indicators (within a 2.1 inch circle) each 6 by 2 mm,
> and no more than 6,100 cd/m2.
> (For light sources that are Red flashes (that have a 590 nm
> wavelength or longer) the values for luminance in this note should
> be divided by 8.)
>
> (For comparison, the maximum brightness of a white screen on an LCD
> computer monitor is about 200 to 400 cd/m2)
>
> RATIONALE: The hardware flash values are based on the CIE Small
> Angle Disability Glare Equation in Johannes J Vos "On the cause of
> disability glare and its dependence on glare angle and ocular
> pigmentation" in Clinical and Experimental Optometry 86.6, November
> 2003 and "Commission Internationale de l'Eclairage CIE. CIE
> equations for disability Glare. CIE report #146. Vienna: CIE
> 2002. This equation also includes an age factor. 62.5 was used
> as the age in generating the constants in equation in #5 above.
>
> NOTE TO ACCESS BOARD: the working group came up with the
> definitions for âgeneral flash and red flash thresholds for
> hardwareâ (above) after much effort but there was NOT sufficient
> time to explore them as much as necessary to come to consensus on
> them. The âgeneral flash and red flash thresholds for hardwareâ
> therefore DOES NOT HAVE CONSENSUS. What the group did consense on
> were the following
>
> 1. very bright point sources or very bright small sources can
> be a problem (per Graham Harding)
>
> 2. Very bright point sources or very bright small sources
> should be allowed if they flash less than 3 per second
>
> 3. Flashing above 3 per second should be allowed if is as
> equivalently safe as with the Software flash thresholds.
>
> 4. Some metrics for identifying âequivalently safeâ were
> created but more time is needed by everyone to study them and their
> derivation before they are used by anyone including the Access Board.
>
> 5. The numbers were included in this report in order to
> facilitate review by different parties.
>
>
>
> general flash and red flash thresholds for software/content
>
> a flash or rapidly changing image sequence is below the threshold
> (i.e. software or content passes) if any of the following is true:
>
> 1. there are no more than three
> General Flashes and / or no more than three Red Flashes within any
> one-second period; or
>
> 2. the combined area of flashes
> occurring concurrently occupies no more than a total of .006
> steradians within any 10 degree visual field on the screen (25% of
> any 10 degree visual field on the screen) at typical viewing distance
> where:
> · A General Flash is defined as a pair of opposing changes
> in relative luminance of 10% or more of the maximum relative
> luminance where the relative luminance of the darker image is below
> 0.80; and where "a pair of opposing changes" is an increase
> followed by a decrease, or a decrease followed by an increase, and
>
> · A Red Flash is defined as any pair of opposing
> transitions involving a saturated red.
>
> Exception: Flashing that is a fine, balanced, pattern such as white
> noise or an alternating checkerboard pattern with "squares" smaller
> than 0.1 degree (of visual field at typical viewing distance) on a
> side does not violate the thresholds.
>
> Note 1: For general software or Web content, using a 341 x 256
> pixel rectangle anywhere on the displayed screen area when the
> content is viewed at 1024 x 768 pixels will provide a good estimate
> of a 10 degree visual field for standard screen sizes and viewing
> distances (e.g. 15-17 inch screen at 22-26 inches). (Higher
> resolutions displays showing the same rendering of the content
> yield smaller and safer images so it is lower resolutions that are
> used to define the thresholds.)
>
> Note 2: A transition is the change in relative luminance (or
> relative luminance/color for red flashing) between adjacent peaks
> and valleys in a plot of relative luminance (or relative luminance/
> color for red flashing) measurement against time. A flash consists
> of two opposing transitions.
>
> Note 3: The current working definition in the field for "pair of
> opposing transitions involving a saturated red" is where, for
> either or both states involved in each transition, R/(R+ G + B) >=
> 0.8, and the change in the value of (R-G-B)x320 is > 20 (negative
> values of (R-G-B)x320 are set to zero) for both transitions. R, G,
> B values range from 0-1 as specified in ârelative luminanceâ
> definition. (Harding and Binnie 2002)
>
> Note 4: Tools are available that will carry out analysis from video
> screen capture. However, no tool is necessary if flashing is less
> than or equal to 3 flashes in any one second period (content
> automatically passes (see #1 and #2 above)).
>
>
>
>
>
>

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