Thread Subject: Re: 2.1-B - Luminance Contrast for Legends

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From: Gregg Vanderheiden
Date: Fri, Oct 12 2007 8:55 AM

I think this is good. Nice work.



A couple comments





1) I think luminosity is often used when products don't actually give off
light. But Tom Albin may know that answer better and I am happy with
whatever the usual term in industry is for labels. In fact I would
recommend that whatever the usual term used in industry when talking about
labels be used.



2) For the 1st note - we need to remove "location". All of the keys on
the keyboard have a unique location. In fact all physical controls have
one by definition (except soft keys).



3) For the 3rd note : how about..

Note 3 : Where keys have multiple labels the primary label must meet this
provision. Secondary labels may also meet the provision or be at a lower
contrast to visually simplify the key. Lower contrast secondary legends
should be used sparingly and preferably only for functions that can be
attained in other ways.



4) We discussed but didn't come to conclusion regarding use of 3:1 or 5:1
etc. What might be helpful to the full TEITAC would be so have some
printed examples of the different contrasts in different colors and typical
fond sizes for the group to look at next time we meet. I think 3:1 is
the recommended minimum contrast for mainstream population - but I don't
know if that is good enough overall (e.g. the problem people with low vision
encounter is labels that are worse than 3:1) or whether 3:1 is a problem
for them. I think we DO have to be particularly careful here since users
cannot adjust the contrast and everyone must use exactly the same. So a
lower limit than our other limit may be appropriate. I just don't know.
Perhaps it will turn out to be a lower contrast but have some limit on the
low end. (e.g. dark on dark yields a reasonable contrast ratio
mathematically even though it is unreadable due to quirk of math unless you
require a minimum difference at the low end). What formula are we
proposing for calculating the contrast for labels? Same as for other
contrast ? (L1 + 0.05) / (L2 + 0.05) [the 0.05 would have to be
adjusted depending on the full scale of L1 and L2. what is the full scale
reading of "luminance"? ]








Gregg
-- ------------------------------
Gregg C Vanderheiden Ph.D.






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Subject: [teitac-committee] 2.1-B - Luminance Contrast for Legends

Below is a proposal for language regarding luminance contrast for legends.

Based on the discussion for displays, I'm proposing changing "contrast
ratio" to "luminance contrast". The Dictionary for Human Factors and
Ergonomics (ISBN 0-8493-4236-8) defines "luminance contrast" as follows:
Luminance Contrast = "a measure of the physical relationship in luminance
between two adjacent, non-specular surfaces under the same general
illumination and immediate surroundings, generally defined by an equation
similar to Cl=deltaL/L."

2.1-B - Luminance Contrast for Legends

If the legend or instructions on the device are the only means of conveying
information, then the luminance contrast shall be at least 3:1.

Note 1 : If other means of conveying the information in the label or
instructions exists (e.g. uniquely tactilely discernible though shape and/or
location), then the luminance contrast requirement does not apply.

Note 2: This requirement excludes product information labels, such as the
regulatory labels, where information can be found in other sources
associated with the product either in hard- or soft copy format.

Note 3: Additionally, I think we need to convey at least for computers that
there are different levels. E.G the alphanumeric labels are the primary
labels and should meet this convention; however, the secondary functions
(such as the blue numbers on an embedded numpad on a notepook) should not
meet this convention as they are infrequently used and in the case of the
numpad may add to visual clutter and additional confusion relative to the
keyboard interaction.

Please comment or provide feedback.

Thanks,

Rob

Rob Nerhood | Experience Design Group | Ergonomics Engineer
Dell, Inc. | One Dell Way | Round Rock, Texas 78682 - 7000
direct 512.723.2763

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