Designing signs is a balancing act of blending parameters, colors, letters and graphics into a single piece whose function is to be noticed, to inform and to bring in revenues. In discussing the effectiveness of a sign, we must address three factors that dominate the design process: visibility, legibility and readability.
They are defined as follows:
Visibility: The purpose of having a sign is so the intended audience “notices” the sign and reads the message. Why do you think truck stops along the interstate use 100′ tall pylon signs with 8′ tall gas price numbers? Visibility is about being seen: Can you see the sign from the highway, yes or no? There are at least four factors that affect visibility: shape, size, color and location. An effective sign is one that makes the best use of all four of these factors based on the environmental conditions at hand.
Legibility: In the sign industry, this means, “Can you tell if that is a capital D or a lowercase P from 300 feet away?” Does the font have a unique style that makes it hard to recognize? If so, you may want to reconsider your options.
Readability: Have you ever looked at a sign with a lot of copy and felt your eyes strain while reading it? If your eyes strain, the designer either used the wrong font, the wrong size of letters or incorrect spacing and kerning, conflicting colors… the list goes on and on.
Calculating Optimum Legibility
If your sign is 35 feet tall and you need it to be legible and readable at 300 feet, what formula do you use to calculate letter height? Calculating this is fairly complex and involves the use of a left-handed abacus, however an easy shortcut is to simply add a zero to the letter height (in inches) and convert the number to feet. Follow this example:
Start with your letter height of 6 inches, then add a zero to it and change the measurement from inches to feet. That means a 6-inch-tall letter would have an optimum legible distance of 60 feet. Letters 4 inches tall are best read at 40 feet and 12- inch-tall letters are best viewed at 120 feet, and so on.
To have optimum legibility at 300 feet, the letter height needs to be at least 30 inches tall. Many of the digital display and plastic letter companies offer useful charts that show letter height readability distances for letters from 1 inch all the way to 60 inches tall. Posting one of these charts near your desk is always a good measure.