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sidetrack RE: Color & contrast- response to Lee's message

From: Charles McCathieNevile <charles@w3.org>
Date: Wed, 17 Apr 2002 12:24:37 -0400 (EDT)
To: Lee Roberts <leeroberts@roserockdesign.com>
cc: "'Web Content Guidelines'" <w3c-wai-gl@w3.org>
Message-ID: <Pine.LNX.4.30.0204171213580.19434-100000@tux.w3.org>
I agree with Lee, Al, and John, that people need the choice because there are
different situtations.

But I thought I would try to tackle the point below.

In a light-on-dark screen, where there is a large diffusion effect, the
letters will "bleed over". So it becomes hard to distinguish a circle from an
octagon. In dark-on-light the light background bleeds over the dark
characters, to the point that it can make them almost disappear. When
computers were often used with poor-quality televisions or monitors for
screens light-on-dark was by far the preferred mode, because it was much
easier to read. The changeover tended to come with quality screens and window
systems - in the early 80s with the Macintosh, the 90s with windows, and even
today many people who use unix or DOS command-line systems work in

As well as better quality screens makng it easier to read, there is the
impact of the light on the eyes to consider. Backlit LCD or "normal" CRT
monitors are bombarding the eyes with light in a dark-on-light setup, less so
the other way around, although there is a higher effective contrast (a little
bit of light stands out in the dark. A little bit of dark is masked by the
presence of so much light). Each can lead to different kinds of "afterburn" -
the effect that comes from staring at the sun too long.

(And if you do use a screen a lot, go outside on a dark night and look at the
ground. Those little glowing worms and bugs aren't there - they are burnspots
in your eyeball...)


On Wed, 17 Apr 2002, Lee Roberts wrote:

  You make a very interesting point although the remainder of you comments
  seem to contradict the single point that stands out so heavily.

  "Light diffuses, dark doesn't."
  If light diffuses then that would mean that it is harder to read against a
  dark background that doesn't diffuse.  The light simply gets squished, like
  the article from Microsoft stated, when it is placed on a dark background.
Received on Wednesday, 17 April 2002 12:24:37 UTC

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