Although the two terms are often used interchangeably, readability and legibility are actually two quite different terms. Readability pertains to how easily words, sentences, and entire blocks of texts can be read by the average reader. The more readable a text is, the less energy someone has to expend while reading. Legibility, on the other hand, is a measure of how easy it is for the reader to distinguish one letter or character in a text from another. More legible fonts usually have higher x-heights, which is a topic that will be discussed later on.
The average reader probably never gives font more than a passing notice, whether they are reading a magazine or a web page. All high school book reports are created with that functional workhorse everyone knows and loves: Times New Roman. Font is font, most people will say, and as long as the reader can decipher it without having to think too hard, what is the difference? Well the truth of the matter is, according to scientific studies both new and old, choosing the correct font and font weights for the occasion can have a huge impact on how readable a piece of writing is to the average reader.
Luckiesh and Moss
The potential readability of different fonts was first studied in depth by two American men, Matthew Luckiesh and Frank Moss, in the late 1930s. Luckiesh, a physicist from Iowa who in his time was known as the “Father of the Science of Seeing,” conducted thousands of tests concerning readability and was greatly concerned with the mystery of human vision. He once famously remarked: “Suppose that crippled eyes could be transformed into crippled legs. What heart rending parade we would witness on the busy street. Nearly every other person would go limping by. Many would be on crutches and some on wheel chair.” Luckiesh had a passion for the complexities of human vision, and his meticulous dedication was evident in his experiments.
One of the most comprehensive tests that Luckiesh and Moss conducted measured readability via an increase or decrease in the spontaneous blink rate of the reader. While reading, a person’s rate of blinking is naturally slowed down, due to the concentration required for the task. However, for subjects reading less readable pieces, the blink rate was proven by Luckiesh and Moss to speed up, indicating more fatigue for the reader and a greater amount of energy expended while reading. Luckiesh defined readability as the effort required of reading, as opposed to the speed at which the passage could be read or total comprehension of the passage. He created and introduced this definition of the term to academia. The spontaneous blink rate test proved conclusively that different fonts and also different font weights (light vs. medium vs. bold vs. extra bold) had a profound impact on a passage’s overall readability.
The work of Luckiesh and Moss in regard to blink rate was discredited by a researcher named Miles Tinker. However, a later fatigue researcher named John Stern conducted still more research on the subject, which offered definitive proof that Luckiesh and Moss were correct in their findings all along. Their research is still held in high esteem to this day.
Does Font Weight Make a Difference?
One of Luckiesh and Moss’ most infamous research experiments pertained to font weight (the darkness of the text). They tested the four weights mentioned above: light, medium, bold, and extra bold. Their findings were surprising, and definitely have bearing for today’s writers and layout designers. Their tests, which measured the reader’s blink rate with the aid of a Linotype, found that the reader’s speed of reading increased slightly from light to medium type, but then stayed relatively the same. However, the surprising find was how the text’s readability was affected by the font weight.
According to the experiment, readability increased sharply from light to medium, the decreased drastically from medium to bold. On the surface, this is a surprising outcome. Conventional wisdom at the time postulated that the more visible a font was, the greater its readability. Therefore, it was assumed that the extra bold font type would be the most readable for the average reader. Luckiesh and Moss, however, found that extra font weight made the text as a whole harder to read. The reader’s blink rate increased sharply as the text got darker, meaning that while bolder font is obviously more attention grabbing, it also taxes the reader much more than medium font. This is definitely something that today’s typesetters need to take into consideration when choosing font weights and laying out web pages.
X-Heights and Legibility
X-height, also referred to as corpus size, is a term pertaining to the distance between the baseline and the mean line within a given font. This is a little difficult to explain in text, but essentially x-height is the height of the letter x, as it starts on the baseline (as opposed to a “p,” which has it’s highest point on the mean line but extends below the baseline) and has its highest point exactly on the mean line. It is generally agreed that fonts with higher x-heights are more legible when compared to fonts with lower x-heights, although like most things within the typesetting community, it is a hotly debated issue. Many typographers actually argue that the leading within a text is more important for legibility. Leading (or Line Spacing) is the amount of vertical space between the lines. With less leading, a typesetter can fit more words on a page, which could make the text either more or less readable, depending on how crammed together the writing is. More leading, on the other hand, would make the characters within the text much easier to distinguish, and therefore much more legible.
Legibility is all about being able to distinguish between different letters within a text. Although there is currently no universally accepted method for quantifying font legibility, it does not make legibility any less important for typesetters.
The Supposed Value of Ligatures
Although fairly uncommon in conventional typesetting, the readability of ligatures are the subject of an extremely hot debate within the typesetting aficionado community. For those who are unaware, a ligature is when two or more graphemes(which are equivalent to letters, in the English language) are combined to make a single symbol or glyph. Ligatures are extremely common in Old English, and have been carried into current usage by purists. The most common Old English ligature, called “ash,” is a combination of the letters “A” and “E.” The combination of the two letters was so popular, in fact, that it has earned the position of an actual letter in languages like Icelandic, Norwegian, and Danish. Before the advent of the Gutenberg printing press, when every written word in every manuscript and book was painstakingly subscribed by hand, the benefit of ligatures was clear; they were much less work for the writer. Also, they were so common that the reader absorbed and comprehended the abbreviation without a second glance. Nowadays, however, the supposed benefits of ligatures is up for debate.
The Ligature Controversy
Some typographers believe that the smooth transition between letters created by ligatures aids in readability. The letters become more compact, and therefore the eye can recognize and internalize them faster, which makes for smoother reading. Many typographers agree that ligatures make for more streamlined, more readable text. In spite of this supposed agreement, the benefit of ligatures is conventionally deemed to be so slight as to be almost undetectable.
However, there is a large group of typographers that argue that the archaic nature of ligatures makes it all but useless for today’s reader. Because letters are so rarely combined in conventional English writing, these progressives make the claim that ligatures actually hang reader comprehension up, as they are unused to interpreting the unique shape a ligature creates on the page. Whatever your opinion on ligatures may be, remember that they have existed for thousands of years, and there must be something behind that.
A Standardized Legibility Test
Luckiesh and Moss developed a fairly universal go-to test for the readability of a font in the 1930s when they tested the reader’s blink rate. It is a quantifiable method for measuring how much strain specific fonts put on a person’s eyes. Unfortunately, there is currently no universally accepted method for measuring how legible a specific font and typesetting is. There are quite a few conventionally accepted fonts that are deemed highly legible, a few of them being Times New Roman, Garamond, Minion, Charter, Georgia, Goudy Oldstyle, Dante, Clifford, Hoefler Text, Constantia, Galliard, Electra and the like. These fonts are commonly used for legal forms, reports, standardized test, and quite a bit of uninspired signage. However, because there is no universal method for testing legibility, it is easy for contention to spring up between preferences for various typefaces. It is also quite easy for an inexperienced typesetter to foul up a perfectly legible font, either by negative tracking, inadequate linespacing, light inking, or artificially condensing the characters.
As of now, legibility is almost purely a matter of personal preference. Fonts are compared to each other, put side by side and analyzed for speed and ease of reading. It is an extremely imperfect system, and there is a gigantic margin of error with this method of analyzing legibility. Until a method for testing and quantifying typeface legibility is developed, there will always be conflict within the typesetting community.
Finally,Typesetters and font enthusiasts are a fickle and contentious bunch. There will always be arguments over Georgia vs. Minion for legibility, italicized vs. boldface font for visibility, and ligature vs. not for readability. Fonts are a flighty mistress. Luckiesh and Moss set a fantastic groundwork for bringing some of the Empirical method into the largely preference-based field of typography. There is still a great deal to be done, and the debate rages on between different font choices and how various readers relate to them.