Commercial Integrator May 2021 - 12

AV BRAINS & BRAWN

In Displays, Size Matters
We can argue about the importance of each component in a system, but there's no doubt that the size
of the display is critical. by Alan C. Brawn
EVERYTHING in a commercial AV system
is critical to the success that we see on
screen but suffice it to say the display is the
culmination of all that goes into it.
If we accept this premise then the
selection of a display appropriate for the
environment and the viewer is of paramount
importance. The keywords here are appropriate, environment, and viewer.
One thing to get out of the way up
front are the display technologies at our
disposal. Not to play the " back in the day "
game with you but we only had one type of
display technology and that was projection.
Many of us lived through the evolution
of lumen light output to something more
useable (3,000+) and even more of us lived
through the early days of flat panel displays
as we evolved from plasma to LCD and
more recently variations of OLED/QLED etc.
Of course, today is the dawning of a
new age, fine pixel pitch dvLED. For those
keeping score I did the history in one short
paragraph. The point is that today we have
a plethora of excellent display technologies
at our disposal.
The more elemental question is: How
we are utilizing those technologies in our
system designs?
Each of the display technologies today
can produce excellent images in the right
environments. I suggest that selecting the
appropriate display is dependent upon the
environment, the viewer and the budget.
That being said, I have found a disturbing
tendency or maybe just a bad habit on the
part of some. This is the tendency to take
the path of least resistance and simply put in
a flat panel display and call it good enough
all too often irrespective of the viewer.
It fits so just hang it on the wall or suspend it from the ceiling and call it a day. It
may be fine for the physical environment
and ease of installation but perhaps not
ideal for the viewers. This is where image
size comes into play.
Sitting in my home office I have a 75-inch
flat panel on the wall. I am 12 feet from it,
12 Commercial Integrator MAY 2021

CM2105 pp12-13 Brains and Brawn.indd 12

The visual manifestation of our commercial AV work is the display.

and this is a " perfect " size for me. I got to
thinking about the screen size I would need in
a typical office meeting space (huddle rooms
aside) if I were 20 or 30 feet from the screen.
We could use the old 4/6/8 rule of
thumb for image size but back in mid-2016
InfoComm did us a favor and published a
new standard to set ANSI specifications for
screen sizing based on viewing distance.
It is called Display Image Size for 2D
Content in Audiovisual Systems (DISCAS)
V202.01:2016.
The goal of DISCAS was to create a
scientific standard and formulae, based on
human vision, to calculate the screen size
for a project specific audiovisual system
based on audience viewing distance and
the viewing criteria.
To define the maximum viewing distance,
DISCAS is based on two viewing categories, relating to how the system will be utilized. There is basic decision making (BDM)
and analytical decision making (ADM).
For those who want all the details I suggest you get a copy of the ANSI standard
but for this article I will focus on ADM. My
rationale is simple. If you have both BDM
and ADM requirements, your designs
should use the ADM formula.
The DISCAS task group gave us a for-

mula to use. It is Image Height equals
Image Resolution times the Farthest Viewer,
then divided by the ADM acuity factor of
3438. Some brilliant math minds (you know
who you are) calculated the visual acuity
factor based on 20/20 vision.

IH = IR x FV ÷ 3438
To help better understand DISCAS as a
design tool, let's use it for a hypothetical
conference room. Based on architectural
drawings we know the dimensions of the
room and the viewing distances. This will
let us know how large a display we should
specify for the environment.
Let's presume this room is going to be
used for viewing detailed images (spreadsheets, drawings, photos, etc.) thus it would
fall under Analytical Decision Making. In our
example the proposed display will be 1080P
in resolution, due to budget concerns.
This means that we know our vertical
resolution to be 1080. We also know
according to the drawings that the farthest
viewer is 22 feet away from the wall where
the display will be installed.
With the ADM formula (Image height
= 1080 x 22 ÷ 3438) this means our
screen must be at least 6.91' high for
proper viewing. This is 14.1' diagonal for
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Commercial Integrator May 2021

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