Legibility Factors

What factors increase the legibility of type? Which factors can decrease legibility?

The issue of legibility has stirred quite a debate. From some arguing that serif fonts are more legible since they help lead the eye form word to word, but others argue that san serif typefaces are easier to read. Often times its comes down to a matter of preference or opinion when determining legibility.

Certain principles have developed, however, when trying to increase the legibility of type. Principles like the use of all capitol letters in sections of copy have been noted for being more difficult to read. This is due to the letters not having ascenders and descenders, as well as, the letters all having similar shape. Fonts with a large x-height would also be less legible. Other factors such as the size of the type, the length of the line, the letting, the kerning, alignment, light, color and even the paper or medium on which the type is displayed has direct control over legibility.

A line, for example, that contains around 60 two 72 characters is going to be easier to read than a line containing more or even less. Using more than 72 characters makes it difficult to jump down to the next line and continue seamless reading. Using less than 60 characters in a line makes the text appear choppy and interferes with the flow of thought.

High contrast is always a good rule of thumb to increase legibility. With road signs reflective paint is used to make the sign for high contrast at night as the darkness decreases legibility. Studies have reveled that a 30 to 50 percent contrast is necessary for legibility for 75 percent of the population.


Resources:
Graphic Design School 3rd edition pages84, 85

http://pubsindex.trb.org/view.aspx?id=58795

http://trex.id.iit.edu/visiblelanguage/Feature_Articles/Roxane/Roxane.html

The human factors of transport signs
By Cándida Castro, Tim Horberry Pages 124, 125
http://books.google.com/books?id=zEZWGz9rOZYC&pg=PA126&lpg=PA126&dq=what+factors+increase+legibility&source=bl&ots=Hde4aauZrh&sig=24RkWYl0VbzUhAv91WT2rBxyazw&hl=en&ei=VcnlSpvtGtTQlAffhcDoCg&sa=X&oi=book_result&ct=result&resnum=5&ved=0CBkQ6AEwBA#v=onepage&q=what%20factors%20increase%20legibility&f=false