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Q: visual acuity ( Answered 5 out of 5 stars,   2 Comments )
Subject: visual acuity
Category: Health > Conditions and Diseases
Asked by: sheph7-ga
List Price: $50.00
Posted: 24 Nov 2003 14:46 PST
Expires: 24 Dec 2003 14:46 PST
Question ID: 280176
Reference to a good book(s) that explains how to design panels and
signage that need to be read in low light conditions. Are white
letters on black background the best? What about glare, contrast, and

Request for Question Clarification by omniscientbeing-ga on 25 Nov 2003 11:26 PST

Most "low light" signage information I came across deals with lighted
signs, as opposed to trying to use certain color schemes. Are you
interested in electric signs that use light, or only in signs of
painted letters?

Google Answers Researcher

Clarification of Question by sheph7-ga on 25 Nov 2003 13:13 PST
I am interested in signs and instrument panels that are not electric,
CRT, plasma, backlit LCD, etc. I am trying to find the science of how
to design panels and signage that need to be used in low light
conditions. Instrument panels in an aircraft, panels of sound
equipment used on a dimly lit back-stage, would be two examples. Why
are nearly all aircraft instruments white letters on black beckground?
Why not blue letters on a yellow background? How important is glare? I
know the design rules are related to how colors are seen in low light
but I need a reference that explains the pratical implications and not
just the physiology.

Clarification of Question by sheph7-ga on 26 Nov 2003 04:15 PST
I am familiar with the ADA stuff and have read a lot about road signs.
The technical is fine but what I have found so far tends to talk about
rods and cones and how the eye works in low light. I can't find
research work that talks about tests conducted and implications for
design. While white on black seems to be the standard I can't find the
science back-up. I would like to know more about not only the contrast
but surface texture, width of line, and size of print implications.
Subject: Re: visual acuity
Answered By: byrd-ga on 05 Dec 2003 20:29 PST
Rated:5 out of 5 stars
Hello Scheph7,

Your question may sound simple on the surface, but in practice, as I?m 
sure you already know, the design of visual information display, 
whether signs, or instrument panels or any other means of visually 
conveying information, is an exceedingly complex field, and there are 
no easy answers to the problem. Without knowing your exact application 
for the information you?re requesting, I?ll try to provide as broad an 
overview of available information as I can, with a search strategy 
that will let you locate more on your own as need be.  I?m not sure 
how technical you wanted to get, but since you mentioned a particular 
interest in the science behind the method, I?m including links to some 
very indepth and technical scientific research.

Yes, as you?ve discovered, white on black, or black on white, is often 
the standard color selection for signs of various kinds that will be 
viewed under low light conditions, particularly, as you noted, when 
clarity is critical, such as in aircraft instrument panels.  However, 
although you?ve read the studies on vision and say you aren?t 
interested in the physiology, it is nevertheless important to 
understand that physiology, as it is there where you must begin in 
order to understand the design parameters for low light signage or 
instrumentation.  The white on black combination is based on this 
understanding of the physiology of human vision in both its color 
selection and the highest possible contrast.

Since you?ve already read the information on physiology of the eye,I?
ll just summarize here that the human eye perceives objects in 
daylight and brightly lit conditions using the ?cones? of the eye, 
while in dim light the eye switches to the ?rods? to see.  These 
different structures work differently, and therein lies the science of 
seeing, on which any design of signs, especially for use in low light 
conditions must be based.

When you view objects in daylight, or well-lighted conditions, you are 
viewing with the cones of your eyes, and you are able to see a wide 
spectrum of colors, as well as nuances of shades, patterns and 
textures. In low light conditions, however,  you rather see with the 
rods of the eyes, which cannot distinguish color, nor much of pattern 
or texture.  In fact, one cannot even see straight-on with the rods, 
but one must actually look a bit to the side of an object in order to 
see it.  Look at it straight on, and it will virtually disappear.

In addition, for the rods to be most useful, the eye must be fully 
adapted to the dark, a process which takes about a half-hour. Before 
that time, and also after if the eye should be exposed to bright white 
light for however brief an interval, the sight is somewhere between 
full use of cones or rods, and therefore not fully adapted to either.  
Obviously, this makes viewing in partially lighted conditions the most 
 challenging of all.

These principles are the science behind the development of signs that 
can be viewed in low light, or in both full and low light.  Such signs 
will have the highest contrast possible, and since the rods of the eye 
do not distinguish color, this usually translates to a black and white 
scheme.  Other schemes implement a slightly lesser degree of contrast 
in order to make use of the psychology of color, but still retain 
enough to render the signs useful in all light conditions, including 
low light.

Just to refresh your memory on these pertinent principles of vision, 
here are a few sites with excellent and fairly simple explanations:

?The Joy of Visual Perception:?

?Vision:? (excellent site)

Here?s a study that explain matters in a little more technical detail 
in case you might be interested in that:


All right, you asked for examples of research work that has 
implications for design of signs to be used in low light conditions, 
and there are many reports of such research with the practical 
deductions that can be drawn from the tabulated results. Bear in mind, 
however, that many, if not most studies are on visibility (or 
legibility of signs/instruments) in general.  They look at overall 
factors of conspicuity, including variables such as color, size, font, 
etc. with low light conditions being only one among several factors 
studied.  You need to look through the research to find the pertinent 
sections that deal with results in low light or night conditions.

I should also mention that, not surprisingly, many of these studies 
focus on transportation, probably since there are significant risks 
for adverse effects if traffic signs and other visual displays are not 
readily legible under all light conditions.  However, just because a 
study was done in the field of transportation, that doesn?t mean the 
results cannot be useful for other applications.  And there are 
additional studies in other areas as well.  Here then are some 
examples for you (if the longer links aren't clickable within the 
answer, copy and paste the full address into your browser):


This site for the ?Visual Performance Laboratory? at University of 
South Dakota contains links to technical reports describing work and 
research performed there.  Reports include ? Nighttime conspicuity of 
highway signs as a function of sign brightness, background complexity 
and age of observer;? and ?Optimizing the legibility of symbol highway 
signs,? with links to more:

Here?s a link to a Texas DOT-sponsored study through Texas A&M 
University on evaluation of fluorescent orange signs.  It reports 
results for both daytime and nighttime with interesting results.  You 
might be especially interested in Chapter 4 on color recognition.

This study from University of Iowa is entitled ?Legibility Threshold 
Contrast of Uppercase Text as Seen Against a Dark Background:?,%20Dr_%20Helmut%20T_%20Zwahlen_files/Papers/LEGIBILITY%20THRESHOLD%20CONTRAST%20OF%20UPPERCASE%20TEXT.pdf

University of Ohio ? ?Unlighted Overhead Guide Sign Feasibility Study? 
(Since I had trouble opening the study, this link is to Google?s 
cached version of it ? you might try clicking on the link to the live 
version in case it was just down for some reason when I tried it.):

Also University of Ohio ? ?Nighttime Expert Panel Evaluation of 
Unlighted Overhead Guide Signs,? related to the previous, but with 
emphasis on nighttime:,%20Dr_%20Helmut%20T_%20Zwahlen_files/Papers/Nighttime%20Expert%20Panel%20UOGS.pdf

Another cached copy, this article by Barbara Hale, ?Transportation 
Engineers Helping to Improve Road Sign Readability,? reports on 
studies done at Penn State on the legibility of a new typeface for 
signs.  Their results include much information on its effectiveness at 

From the Texas Transportation Institute is this 2001 study entitled ?
Legibility of Retroreflective Signing Material,? which includes both 
day and night evaluations of materials as well as color recognition: (*Note: 
this PDF file requires you to have Adobe Acrobat Reader in order to 
view it.  If you don?t already have it, you can download it here: )

This site, 
, refers to a 1990 study addressing, among other issues, nighttime 
legibility requirements of highway signs.

Here is a report of a study done by the Florida DOT on elder roadway 
use, and includes both daytime and nighttime evaluation of font styles 
and sizes for street signs and roadway signs, as well as pavement 
markings.  It may be especially interesting as it is well known that 
one of the factors in aging and vision is the loss of the ability to 
see clearly in low light conditions.

Another study on sign visibility for older drivers, including 
nighttime evaluations, this one on ?Improvements in Symbol Sign Design?
 by U.S. DOT Federal Highway Administration:

From Virginia PolyTech Journal of Design Communication, ?The Effect of 
Color Contrast on Message Legibility:?


Ok, as to instrument panels and control panels, research and studies 
for what you ask are just not readily available. That is, nearly every 
study I could find on instrumentation under low light conditions talks 
about some sort of illumination, i.e. LCDs, backlighting, exterior 
lights, etc.  Furthermore, the guidelines given below for instrument 
face and panel design reference other, more standard studies on vision 
and visual perception rather than studies targeted specifically to 
seeing instruments.  Therefore, I think you will have to review the 
information on signs in general, and infer from them various color 
combinations, fonts, etc. which might be applied to your needs.


Since your original question was for a book on how to design signs for 
use in low light conditions, you might want to take note of the 
various texts referenced in the above studies.  Also, there are 
guidelines and manuals online that you may wish to check out, as well 
as design manuals and standards available for purchase. But do keep in 
mind that, as in the case of the studies cited above, such guidelines 
also generally mention low light as only one factor among several that 
influence design parameters, and you may have to do some indepth 
reading to find specific citations on the impact of designing for low 
light conditions.

Perhaps not surprisingly, sign companies are a ready resource for 
design guidelines for signage of various types, and are based on 
principles deduced from the above and similar studies, as well as on 
survey and anecdotal deductions. Here are links to several sites that 
have tips and tutorials for customers on good sign design.  Though I 
couldn?t locate any manuals or texts specifically dedicated to sign or 
panel design in low light, many/most of these guidelines speak to the 
issue of visibility of in low light conditions, and give a lot of 
technical guidance in terms of size of lettering, font selection, 
colors, and materials among other factors.


Flynn Signs & Graphics, Inc. ? Sign Design Tips:

Electromark ? Helpful Hints:
?American National Standards Institute (ANSI) Z535 Sign and Tag 
Standards? ? They state,?These new ANSI standards represent the first 
significant re-write of the sign design standards since they were 
initiated [in 1914]. Of special importance in the new standards are 
the Appendices for each standard. The Appendix to each standard shows 
sign formats, suggested writing styles, type fonts, etc.? Included are 
clickable excerpts from the standards.

?Consider Viewing Angle and Light Level:

?Seven Secrets of Highly Effective Signs:?


The next most useful resource for information on sign design and 
visibility in all light conditions are various governmental agencies 
and departments, including OSHA, USDOT, various state DOTs, and the 
FERC (Federal Energy Regulatory Commission).  Here are several 
comprehensive manuals on sign design that take visibility in low light 
conditions into great account:

The official manual for traffic signs in the United States is the 
MUTCD (Manual on Uniform Traffic Control Devices), and is the standard 
to which most other manuals and guidelines refer.  You can find it 
The 2003 Edition is here:

Part 2 is the section pertaining to signs.  The government does not 
have a printed version of this manual, but the site provides links to 
organizations that have printed it and offer a hard copy for sale.

The U.S. Army Corps of Engineers is in the process of digitizing its 
Sign Standards Manual and plans to make it available on the internet, 
although it is not yet complete.  You can, however, currently download 
the first chapter in PDF format, here:

FERC: ?Safety Signage at Hydropower Projects:? (Be sure to take 
advantage of the clickable appendix links, which often have detailed 
explication of various visibility guidelines.)

Washington State DOT ? Traffic Sign Design Manual:

OSHA requirements for traffic and road signs (very detailed with many 

While not specifically about signs, this book for sale on ?Designing 
Exhibits That Sell? has some chapters about use of graphics, color and 
visual impressions that may be useful to you:


Contained within the FAA?s ?Human Factors Design Standard? are 
standards for instruments and instrument panels that may be of use to 
you.  You can download the handbook for free, but they?ll ask you to 
register.  Also, the download is close to 10 Mb in size, so be sure 
you have room for it.  Here?s the link:

The handbook, however, references MIL-STD (Military Standards), in 
particular MIL-STD-1472, which is the ?Design Criteria Standard ? 
Human Engineering.? This is also available as a download, although it 
is for sale and not for free.  Find it here:
com/ A complete list of standards available for sale is here: http:// In addition, the FAA references several other 
standards, including:

The Nuclear Regulatory Commission (NRC) Human-System Interface Design 
Review Guidelines: NRC: Human-System Interface Design Review 
Guidelines (

The Electric Power Research Institute (EPRI) Department of Energy 
Standard ?Guide to Good Practices for Equipment and Piping Labeling:?

The Federal Highway Administration has published a set of Human Factor 
Design Guidelines, here: ,which 
includes design guidelines on ?Selection of Colors for Visual Displays,
? here: as 
well as other information you may find useful.  Of particular interest 
is the fact that they cite specific rationales for the selections 

This technical report from the University of Michigan?s Transportation 
Research Institute, entitled ?Suggested Human Factors Design 
Guidelines for Driver Information Systems? addresses visual displays, 
and discusses such variables as color, font selection, type size, 
glare and lighting:

The ?Driver Interface Group? homepage is here:

General Guidelines for Advanced Traveler Information System (ATIS) 
Displays (includes supporting rationale):

This report from the Federal Railroad Administration (FRA) is on 
design guidelines for locomotive cabs, and addresses such issues as 
workstation design, including instrumentation layout and visibility, 
controls, labeling, and others in all visibility conditions:

The report above refers to ANSI standards ANSI/HSF-100 1988, which can 
be purchased here:
This article:  
above with regard to its usefulness in actually designing a work 
terminal, and concludes that other standards and guidelines might 
actually be more useful.  In particular it references ISO 9241, the 
European Community international standard.  That can be purchased here:


Here?s a terrific list of resources from ?The Visual Expert? 
pertaining to vision and human factors in design:

Here is a list of references on human factors in design, including 
some to signs and equipment/instrument markings:

And from the International Organization for Standardization (ISO) is 
this list of design standards for signs of various types:

Color Resources ? a page of links to a lot of information on various 
uses of color:

International Ergonomics Association:

American National Standards Institute (ANSI):

American Society for Testing and Materials(ASTM):

Society for Information Display:

United States Sign Council:


You also mentioned wanting a reference book.  Some of the sites listed 
above refer to various texts and books. Also, in the case of the 
standards publications, those must be purchased and the sites provide 
links for doing so. In addition, here are a few other books that may 
interest you.  Again, remember that in sign design, low light is 
considered one of many factors that influence selection of size, color,
 contrast, type, etc.

Sign Design Guide:

Designing Signs - Corporate Signs:

Sign Easy Type Guide:


I hope this information and these links will be helpful in providing 
you with direction to the kind of guidance you?re looking for on sign 
and instrumentation design for use in low light conditions. If 
anything isn?t clear, please do use the ?Request Clarification? 
feature to ask, before rating and closing the question.  I will be 
happy to work with you further if necessary to ensure you have the 
information you need.

Best regards,

Search strategy:  I began by using terms such as signs and ?low light? 
or night without much success.  After a great deal of trial and error, 
the following terms ultimately proved to be the most useful:

"sign design"
"low light" rules OR standards OR manual OR guidelines
signs standards specifications
sign nighttime legibility study OR studies OR research OR evaluation
legibility research study "instrument console" OR "instrument faces" 
OR dials OR 
legibility ergonomics "low light" OR dark OR "poor light" OR night OR 
?designing an instrument panel?
research "low light" "instrument faces" OR "instrument clusters" OR 

In addition, when reading through the results, I looked for additional 
references that I could use for further searching, such as standards 
documents, organizations and other terms, including ?gauge faces? and 
ergonomics, ?human factors? and ?ergonomic design.?
sheph7-ga rated this answer:5 out of 5 stars and gave an additional tip of: $50.00
Great job of research! I haven't had the time to investigate all the
references but they look good. Thank you.

Subject: Re: visual acuity
From: punzel-ga on 25 Nov 2003 19:28 PST
as i understand your question, you are probably looking for something
less technical/expensive than reflective paint, and need to know WHY
certain combinations of colors work better than others.

if you look at blue letters on a yellow background, you'll see that
they "shimmer", making it hard to focus after a few seconds.  also,
hard to see in low light, although you'd think the contrast would be

a good example are highway signs - black on yellow, or black on white,
or white on green.  of course, hwy signs often use special paint, that
has tiny ground up glass beads or other additives to increase

the Americans with Disabilities Act has set some standards for signage
also that might prove helpful to you.  you can check out that info
For a general overview of ADA requirements, go to:

for info on ADA compliance in stadiums & arenas:

and this site has a Color Contrast Chart that shows LOTS of
possibilities and how well they work:

here is a website for airport signage standards, esp. painted ground signs

hope some of this helps.
Subject: Re: visual acuity
From: byrd-ga on 06 Dec 2003 12:50 PST
Hi Sheph7,

You're most welcome. I'm so happy you were pleased with the answer. 
Thank you very much for the kind words, five-star rating and most
generous tip! Should you have any further need for clarification after
you've had time to check out the references, please don't hestitate to

Also, I've just noticed that the link to the Nuclear Regulatory
Commission guidelines didn't paste properly, so here it is: 

Best of luck in your endeavors, and thank you for a very interesting challenge.

Kindest regards,

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