Why white looks bigger than black —the Irradiation Illusion

The term irradiation illusion  was coined by German scientist Hermann von Helmholtz in the 1860s to describe the visual perception in which a light area appears larger than an identically-sized dark area. The effect was observed as early as the time of Galileo, who refers to it in his observations of the sizes of planets when viewed through a telescope at different times of day. The illusion is illustrated below. The white square in the black field on the right seems larger than the black square in the white field on the left. It’s as if the white area on the right spills outward beyond its edges into the surrounding black. At the same time, the white field on the left appears to encroach upon the black square making it shrink.


The drawing below shows how the irradiation illusion can affect lettering. The top halves of the letters shown are clearly bolder looking than the bottom halves. This means that, on a dark background, a white letter with a heavy stroke will look even heavier, sometimes to the point that legibility is compromised. Counter spaces that are already small become even smaller. Interletter spacing shrinks. Heavy white lettering on a dark background can take on an unpleasant bloated look, and the effect is more pronounced as the viewing distance increases. The solution, simply, is to use lighter stroked letters and increase the letter spacing when the background is dark.


This phenomenon of white letters appearing heavier is not always a bad thing. The effect can be put to use at times. It can even save an otherwise weak layout. How so?

Put the Irradiation Illusion to good use

Computer font collections tend to have a disproportionately high number of light faced letter styles. These typestyles are designed mostly for print, not for signs. Times Roman, as an example, is an inherently weak letter style on sign work. It looks fine in print, up close. After all, it was designed for newspapers held at arm’s length, paper whose porous qualities actually help thin-faced letters. Paper, especially newsprint, allows inked letters to bleed a little through capillary action (the printer’s term for this is dot gain). This effect allows the hairline strokes characteristic of many romans to achieve a little more thickness when printed. But in large sizes on signs, the thin strokes of painted or vinyl lettering remain thin lines. Add to this thinness the effect of the irradiation illusion, and the strokes become even thinner. The result is that a large sign lettered in all Times Roman has a distinctly anemic look. In printspeak, the lettering is not ‘black’ enough. It appears insubstantial, weak. The thinnest strokes eventually disappear as viewing distance increases, leaving visible only a series of meaningless vertical strokes. But if you create a reversed color scheme—putting white roman letters on a black background—the letters instantly become a little stronger.

Similarly, the legibility of some scripts can be improved by a dark background. Computer scripts are often so light faced as to be useless for sign work without some kind of ‘stroking’ to beef them up. Using a dark background can sometimes solve the problem with minimal effort.

Before computer fonts

In the days of painted signs, the expanding/shrinking illusion of irradiation was a problem easily addressed. For one thing, sign painters did not use fonts [related post:  Sign painters didn’t use fonts], so they were not burdened with picking through hundreds of unusable typestyles to find the few that worked well. Their letter styles, “alphabets,” as they called them, were all hand drawn specifically for sign work. Generally, these styles were not duplicates of typestyles that were created for print. And letterers tended to rely on medium and medium-heavy stroke weights for the bulk of their work. When a light typestyle was required, say, by an insistent client, or when an architect specified a certain typeface, it was easy to thicken the strokes slightly if needed for legibility. This could even be done on the fly during the brush lettering process. When a sign painter used script, it was most often a medium weight, sometimes heavy, infrequently light. Experienced sign painters knew that light faced lettering often produced weak-looking signs that lacked impact.

Good design is rarely accidental

In sign design, legibility is dependent on the interplay of light and dark images. Letter recognition relies not only on the positive image of the letterform but also on the negative space surrounding and within it. When one or the other is overpowering, there is always a compromise of legibility. This is why medium weight letters tend to be the most legible on sign work. It doesn’t mean heavy or light faced letters should not be used at all. Rather, it means using them prudently.

Being aware of, and carefully manipulating, effects like the irradiation illusion can help a sign artist produce good layout. Effective design is not an accident.


My inspiration for this article is an archived blog by UK designer and typographer Jon Tangerine from 2010:    jontangerine.com


Hermann von Helmholtz


Hermann von Helmholtz bio in brief.    from famousscientists.org

Hermann von Helmholtz bio   from Encyclopedia Britannica. His pursuits as a scientist were broad. Perhaps best known for his invention of the ophthalmoscope in 1861, still an essential diagnostic tool used in medicine today.

Hermann von Helmholtz   from the Stanford Encyclopedia of Philosophy. Details of his interests, philosophies, teachings and accomplishments.




Book Review: Signs, Streets and Storefronts by Martin Treu

Signs Streets and Storefronts

Signs, Streets and Storefronts. A History of Architecture and Graphics along America’s Commercial Corridors. Martin Treu (John Hopkins University Press, 2012)

This a history book. But a very focused one.

Signs, Streets and Storefronts uniquely fills a niche in the world of architecture and graphic design history, and will probably stand alone in this role for many years to come.

The evolution of American culture as reflected by its signs, and in particular, by the look of its urban commercial districts, is a fascinating study. Even if you are not so much interested in architecture, you will find this book to be an insightful record of the sign industry in America from its earliest beginnings in the 1700s. Martin Treu is an architect and environmental graphic designer, and his research is painstaking and exhaustive. The pictures alone kept me spellbound for hours (I am a sign designer).

It is captivating to see, through Treu’s eyes, how the design of signs and commercial buildings has transformed through history, reflecting the social thinking of successive generations of architects, advertisers, preservationists  and governmental authorities. The changes brought about in the sign industry by advancing technology, electricity in particular, is a story all its own. This history of signs and storefronts is rich with photographs and well documented.

Published in 2012, if this book is not already on the shelves of many architects I will be surprised. I expect it to become essential reading as a design history.

For a much better and more comprehensive review of this book, see Ann Weiser’s in The Architect’s Newspaper:

Ann Weiser review

Also,  see Amy Korte’s review in Chicago Architecture:

Amy Korte review



Can You “Waste Ballast?”

ballasts picture

A sign guy I know had just come from inspecting an electric sign that was not lighting. I heard him tell the boss to order a ballast that would power three 8-foot fluorescent lamps. Looking up from the catalog, the boss said there were two ballasts available. One would power up to 24 lineal feet, and the other would run up to 28 feet of lamp. The installer said, “Use the one for 24 feet.” I expected him to comment that it was cheaper. Instead, he said, “The bigger one will waste ballast.” I looked up anticipating a smile. I thought he was joking. He wasn’t.

Wasting ballast? His argument was not about price, that the larger ballast cost too much more. He was talking about some kind of “yield.” Like cutting up a sheet of sign board so there is no waste. His idea was that you get the most out of a ballast when you hook it up to its maximum load. I didn’t question his logic at the time. He is no dummy. But I question the logic now.

Whether a ballast’s full capacity is utilized is a moot point, a nonsense argument. The real issue concerns the lifespan of the ballast. How long do you want it to last before replacing it?

Planned Obsolescence

Modern manufacturing methods include the effort to program a product’s lifespan. Engineers design appliances so that the life expectancy will be a little longer than the warranty period, assuming the product is used at 100 percent capacity. If you have you ever had a device fail shortly after the warranty period expired, you know what I’m talking about. So, when you use a sign ballast at its highest rated load, you may be reducing its life expectancy to the maker’s lowest expectation—in the case of a ballast, two years, generally.

That means that you can get more life out of a ballast, or a neon transformer for that matter, by using it at less than the maximum load rating. Is that a good thing, to make a ballast last longer? Well, it depends on your business philosophy.

If you are a proponent of “planned obsolescence” you may want your sign ballasts to fail right after their warranties are expired—to generate more service calls. But this can be a dangerous game. I think most consumers find the idea of planned obsolescence distasteful, as evidenced by the decline in favorable reputation experienced by American car manufacturers when longer-lasting Japanese imports first entered the US market. In the 1920s, US car makers had perceived that the automobile had saturated the market, and they were looking for ways to keep consumer demand strong. Changing the style and design of cars each year was proposed as a good way to do this. And the idea of artificially limiting the lifespan of a vehicle, or its components, was part of this thinking as well. So building a car cheaper would not just be about lowering the sticker price. It was also about built-in obsolescence.

What kind of reputation do you want?

It’s good to remember that most people are not necessarily interested in the cheapest product. Most people do not buy the cheapest car on the car lot. Do you? Other factors, in addition to price, contribute to an automobile purchase. Rather than always wanting the cheapest, what most consumers really want is a good value, and that’s not the same thing.

It’s revealing that US car makers these days are intent on fostering the perception of durability. And it’s true that the average automobile today is more reliable than cars of the past. Hence, the longer warranties many manufacturers offer. The invention of the extended warranty goes a step further. It guarantees a longer lifespan for a product, for a price.

So, as a sign maker, what kind of reputation do you want? Do you want to be known as a shop that builds a cheaper sign that requires servicing more often and may be more expensive in the long run? Or do you want to be seen as a shop that charges a little more but builds signs requiring less maintenance?

One thing is clear. Loading a sign ballast to less than its rated capacity is not “wasting ballast.” It’s simply a way to extend ballast life.

For a more detailed discussion of this subject, see Dan Hale’s article Superior Signmaking (Signweb, 2007). Hale recommends loading a ballast or transformer to 80% of its load capacity, where possible.



Acrylic plastic—How is it made?

Starbucks channels


Polymethyl methacrylate is a plastic containing one or more derivatives of acrylic acid.
We know it simply as acrylic.
It is sold under many trade names: Plexiglas, Lucite, Acrylite, Perspex, Acrilex and Crystallite.

There are two types of acrylic sheet commonly used by the sign industry—cast and extruded.


Cast acrylic is made by injecting the ingredients into molds as a molten liquid, about the consistency of syrup, in one of two ways. The “cell cast” or “batch cell” method is made in sheets in a mold made of two plates of polished glass with gaskets at the edges. The liquid plastic fills the cavity between the two plates of glass and may be heated. Several plates may be stacked to produce multiple sheets of acrylic. After curing, the molds are disassembled and cleaned for reuse.

“Continuous cast,” is a higher production method. The molten mixture is cast between two continuous sheets of polished metal in much longer runs as it goes through a series of heaters for curing. Again, gaskets seal the edges.

Cast acrylic is polished and is known for optical clarity. It is harder than extruded acrylic and less prone to scratch. It is also more heat resistant, which is why cast acrylic cuts so much cleaner when machined, whereas extruded acrylic tends to melt behind a saw blade.


Extruded acrylic is a less costly process and provides the larger share of acrylics used in the sign industry. It is manufactured by forcing the semi-molten acrylic mixture through forms and rollers.

Acrylite FF is an example of an extruded acrylic sheet. Acrylite GP is cast.

Airplane and helicopter canopies are made from cast acrylic because of its optical clarity.
Plastic sign faces are mostly extruded acrylics.

Electric signs and sign goobers

Most sign companies in the US do not have real, live electricians on the payroll. The typical sign shop doesn’t want to pay what a licensed electrician would demand for wages, so lesser paid employees are trained to assemble and wire internally-illuminated signs, and service them after installation. The learning curve is not steep, as electric signs are very simply built. These employees will have varying degrees of electrical knowledge and ability, ranging from people who are very experienced to complete novices. Pre-cut knock-down kits are available that allow practically anyone to put together lighted signs with a minimum of fabrication equipment. They can be assembled with screws, high-bond adhesives or by welding. Translucent vinyl lettering can be used for the plastic faces, eliminating the need for painting. This type of work can be done by the most unskilled labor. It can be done in someone’s garage.
In fact, if the general public in this country knew how inexperienced some people are who work on electric signs, they would be surprised.
In the US, using unskilled workers for this type of electrical work is usually not a problem for licensing authorities. Sign companies in most municipalities are legally allowed to do limited electrical work without a license, without any credentials at all, in fact. Further, after paying the fees and receiving an inspection of a sample completed sign, most any shop may receive UL certification.

So just as practically anyone in this country can start a sign company and be a “sign designer,” practically anyone can make electric signs, too. I’m not saying this is bad, necessarily. But just as I would like to see sign makers strive for better design work and a better understanding of design principles, I would also like to see sign makers improve their knowledge of electricity and their understanding of basic electrical troubleshooting.

Though this site will be primarily devoted to design, there will also be posts related to lighted signs.