Message Display Characteristics and Legibility

Mobiles are used differently from desktops, and even most print use of type. They are closest, perhaps, to signage in that they must be comprehended by all user populations, under the broadest possible range of environmental conditions (e.g., poor lighting) and at a glance. The typical mobile user is working with the device in a highly interruptible man- ner, glancing at the screen for much of the interaction. The message display is competing with millions of other stimuli in the visual field. Therefore, mobiles must be designed to stand out appropriately, beginning with legibility.

The following is a list of legibility guidelines for mobile devices:

• Avoid using all caps for text. Users read paragraphs in all caps about 10% slower than mixed cases. (Nielsen, 2000).
• With age, the pupil shrinks, allowing less light to enter the eye. By the age of 80, the pupil’s reaction to dim light becomes virtually nil (Nini: 2006). Use typefaces that have more visually distinct characters in certain cases, while still maintaining a desired unity of form.
• Older viewers with aging eyesight can benefit from typefaces that have consistent stroke widths, open counterforms, pronounced ascenders and descenders, and wider horizontal proportions, More distinct forms for each character (such as tails on the lowercase letters “t” and “j”).
• Try and use plain-color backgrounds with text because graphical or pattern backgrounds interfere with the eye’s ability to discriminate the difference.
• Sans-serif is often the default choice as it works well enough for all uses, at all sizes. Serifs may or may not help with readability, so there is no special reason to use them. Consider using default faces that carry through the sensibility of the OS, such as Helvetica (iPhone’s default typeface). Verdana is also good, as it has a larger x-height and simpler shapes, designed specifically for on-screen readability. There are numerous mobile-specific faces as well.
• Almost all text should be left justified, only items such as titles centered.
• Use typefaces that have strong and open counters (or "counter-forms") – often, using squared-off shapes for small counters is a good idea.
• Use typefaces with un-stressed forms – straight, even-width lines.
• Consider how different pixel densities across mobile platforms affect physical sizes of elements. Using Ems to define the size of fonts in CSS may provide ease.

Message Display Readability

As we discussed earlier, legibility is determined by how we can detect, discriminate, and identify visual elements. But legibility is not the end to this process of designing effective mobile displays. We must make sure they are readable. When readability is achieved, the user can then evaluate and comprehend the meaning of the display.

Readability is based on the ease and understanding of text. It is determined by whether objects in the display have been seen before. Thus, readability is affected by the message’s choice of words, the sentence structure, appropriate language, and the reading goals of the user (Easterby 1984).

Reading Modes

In September 2004 Punchcut worked with QUALCOMM to develop a typographic strat- egy with respect to its custom user interfaces within its mobile operating system and ap- plications. In that study, Punchcut determined three modes of reading and understanding behavior that occur within the mobile context (Benson 2006).

These modes consider the duration and size of focus for textual attention:

Glance

• Users are in “Go” mode and they need quick access to frequent and/or critical tasks. Their focus is distracted and minimally on the task at hand. Users rely on shape and pattern recognition in this mode.

Scan

• Users are sorting and selecting, scrolling through lists of choices and options. They apply more focus than when glancing, but not their entire focus.

Read

• Users are reviewing and comprehending information, and apply their entire focus on desired information.

Language Requires Context