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Neon Legibility

Proper design boosts signage impact



Previously I discussed the physical aspects of human eye resolution and sign visibility. But these aren’t the only important factors in creating effective neon signs. Like a headline, a sign’s main function is to deliver a bold message. Optimizing a sign’s appearance requires awareness of both psychological and physiological factors.

This month, the physicist treads on the foreign territory of psychology — a subjective, rather than quantitative, discipline. Because psychological effect is an important factor in sign design, it’s worth taking a detour into "soft science."

Psychology of reading

When I asked a psychologist to define the process of reading a neon sign, he gave me the following, not-so-simple response: "Reading of luminous advertising resembles conscious realizing of all typical details of the lettering presented and processing the content received by comparison with values stored in the brain to obtain a reproduceable statement."

After some clarification, I began to understand his description. In simple terms, it means that the human eye only reads clearly when its focal area doesn’t move. To read written text, the eye must divide it into individual viewing steps. During these viewing steps, the eye spends approximately 90% of its time fixed on "resting points," whereas the time required for the eye to move between resting points represents only 10% of the viewing step’s total time.

At a normal reading distance, only six to 10 letters of standard printed text can be clearly recognized with a single fixation. The brain’s influence on text recognition is demonstrated by the fact that people read useful words faster with fewer fixation points than is true for random letter combinations. When reading a letter, the eye divides the character into certain repetitive shape elements typical of a given culture (for example, Western, Arabic or Far East styles) and combines these with similar letter shapes.

On signs, this means that short texts are easier to read than long texts, and well-known words are more conspicuous than unfamiliar expressions or names.

History of fonts

The development of today’s alphabets took several thousand years. In the beginning, cave drawings depicted entire scenes. About 10,000 B.C., these scenes were divided into smaller pictorial elements ("pictograms") describing one specific element of a scene. Five thousand years later, pictograms began to signify single words (for example, Egyptian hieroglyphs).

These evolved into early syllable alphabets like the Japanese still use today. Approximately 2,000 years ago, letter alphabets were developed. Gutenberg’s invention of printing was a major step in the development of fonts, allowing standardized letters to be created as an alternative to handwritten text.

The ability to reproduce standard letters allowed artistic design of complicated fonts such as "Fraktur." As books became more popular, fonts were simplified to reach a wider audience. Influenced by British culture, "Antiqua" style letters were developed. Contemporary examples of this style are the "Times" fonts popular for many of today’s word-processing programs. Easier readability became more important at the end of the 19th century, leading to creation of modern sans-serif fonts like "Helvetica."

Letter design

Let’s examine the elements of letter design. One major element of a letter’s shape is its contour line. Fig.1 shows examples of uniform, double and broken contour lines. Because tube diameter is uniform in single-stroke neon letters, designers should use only fonts with uniform contour lines.

Deriving mainly from the historical roots of particular fonts, serifs do not facilitate the eye’s recognition of sign letters (Fig. 2). Although serif fonts are popular for channel letters, single-stroke tubing should not be used to illuminate these styles. In general, serif fonts should be limited to enclosed channel letters or very large neon letters with multiple rows of glass. Bending serif letters is also more difficult for glassworkers, thus increasing the sign’s overall cost and the chance of neon breakage.

Another readability factor is the ratio of upper-case letter height to lower-case height (Fig. 3). Today, a height-ratio range of 6.5:5 to 7:2.5 is considered easy to read, and contemporary fonts reveal a trend toward equalizing the heights of upper- and lower-case letters.

Calculating readability

The width-to-height relationship of letters is very important for readability of neon signs at various distances. To quantify readability, physiologists define a "distance factor." Derived from experiments, this number is arbitrarily designated as 666, representing the maximum value for a block-style letter "E." The greater this distance-factor number, the better the readability of a specific letter.

TABLE 1: Distance factors for black Helvetica letters (white background)
Lighting conditions Font type Width/height value Distance factor
Average Condensed 0.5 255 to 320
Average Standard 0.75 290 to 370
Average Bold-faced 1.0 340 to 435
Good Condensed 0.5 360 to 455
Good Standard 0.75 430 to 540
Good Bold-faced 1.0 505 to 645

In 1951, distance factors were established and standardized in Germany for standard, black Helvetica letters on a white background (Table 1). According to this chart, condensed fonts are more difficult to read than standard or bold fonts. Also, not all letters of the alphabet are equally legible. For this reason, an empirical, "fidelity" factor is another element in signage visibility (Table 2).

TABLE 2: Fidelity factor for capital block letters
(The higher this factor, the better visibility.)
A=1.30 B=0.85 C=1.07 D=1.03 E=1.00
F=1.04 G=0.92 H=0.92 I=1.41 J=1.21
K=1.06 L=1.19 M=1.13 N=1.00 O=1.06
P=1.04 Q=1.06 R=0.97 S=0.95 T=1.15
U=1.07 V=1.08 W=1.13 X=1.08 Y=1.04

This information suggests that perhaps a given neon sign should be broken up into two lines instead of trying to squeeze it into a shop window as one line of condensed letters. Furthermore, using italics or script lettering might seem to make the copy flow better, but these styles also reduce a sign’s maximum readable distance.

Based on many neon shop-window signs I’ve seen in the United States, letter spacing is frequently a neglected factor in design.

Sometimes your client can encourage poor design by making requests like, "I want a red neon sign reading ‘Restaurant’ in my window with at least 5-in.-high letters. The width of my window is 29 in., so just make it fit."

As many experienced sign painters remember, proportionally spaced text requires less width than fonts with constant spacing (typewriter style). Thus, when the sign designer suggests, "Let’s make it a little more proportional," the result is frequently a very bright sign with its letters so tightly squeezed that it’s impossible to read.

As a standard rule of thumb, the minimum letter spacing should be at least 0.4 times the letter height. Within reason, increasing spacing improves readability. But if the spaces are too large, the sign appears as single letters, not words.

Sample calculation

Now we have all the necessary information to calculate lettering proportions for a given sign. Using the "Restaurant" text in Helvetica as an example, suppose that the available window space is 10 ft. wide x 4 ft. high. The client wants good readability from a subway station located 300 ft. from the sign.

For Helvetica block-style letters, we use a nighttime distance factor of 400-420 (410 is the median value). In our word "Restaurant," the minimum fidelity factor from Table 2 is 0.95 for the letter "S." The required letter height "H" (Fig. 3) is calculated by the formula H = reading distance




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