A few weeks ago, somebody wrote in to us asking about the best size and type of text to use on digital signage displays.  At the time, I was researching various aspects of ADA compliance for interactive kiosk applications (which will be the focus of a future blog entry), and I came across some interesting information on the subject.

Not surprisingly, there hasn't been a lot of research focused exclusively on digital signage.  However, our brethren from the world of printed signage have spent a good amount of time, energy and money on this very subject, so I think that it's only proper that we should borrow some information from them.

But before we simply take the tried-and-true rules of static printed signage and try to attach them to their dynamic, electronic counterparts, it's important to look at the differences between these two types of display media.  For example, most printed signs would fall under the heading of a reflective display -- that is, ambient light bounces off of the signage material (whether it be paper or vinyl or something else), and into the eyes of the viewers.  Reflective displays are good in high ambient light conditions like daylight or bright indoor lighting.  Likewise, they don't work very well in poorly lit areas, since the dimmer the ambient light, the dimmer the sign will appear.  On the other hand, most digital signs are emissive, in that they actually produce their own light.  Thus, they are most noticeable in low-light conditions, since they would be brighter than their surroundings, but they can get washed out in bright-light conditions.  Also, while a good, high-resolution digital sign (like a plasma display or LCD monitor) might contain about 70 pixels per linear inch, paper output typically has 300-600 dots per inch, offering much higher resolution.  This means more vibrant graphics and crisper, easier to read text than electronic displays.

Having gotten that out of the way, most of the design rules that apply to static (printed) signage also apply to digital signs.  For example, the most obvious one: bigger text is easier to read, and can be seen from further away.  What's a good rule of thumb here?  As this article from Signweb suggests, text one inch high can be seen clearly from 25 feet away.  You need to increase the size by about an inch (vertically) for every additional 25 feet of visibility.  A slightly different take on visibility can be found here, where the authors suggest that 3 inch-high text can be seen from up to 100 feet away, but will have maximum "impact" at about 30 feet.  This page also has, "[t]he exposure time for exterior signage is: Drive-by traffic: 3 seconds, Walk-by traffic: 11 seconds."

Next, think about the use of color and contrast on your digital signage.  Since you're likely to have moving images behind or next to your text, the background color might change significantly while a viewer is trying to read your message.  Consider these words of advice from Signweb:

"[W]ords that comprise initial capital letters followed by lower-case letters are more readable than words that employ all upper-case letters. On the other hand, from a greater distance, signs that incorporate all capital letters are probably more legible.

Outlines and drop shadows can also improve readability. For example, heavy, black, drop shadows can create the right contrast and improve readability. Although black is frequently used for drop shadows, it isn't the only color you should consider. For example, if you're using gold lettering on a bright-red background, use a dark red for the shadow -- the dark red will soften the transition from the gold in the foreground to the red background."

Finally, while many principles of static signage do apply to dynamic digital signs as well, some decidedly do not.  For example, it is common wisdom that a serif font is easier to read (and therefore allows for greater comprehension and recall) than a sans-serif font.  (For those who are not typographically inclined, this is a nice primer on typeface terminology).  While this is true in the print world, it is not true for digital signs, where sans-serif faces reign supreme.  The main reason for this is that the serifs (little dangly things that hang off of the edges of your fonts -- think Times New Roman) typically get blurred out by monitors using various anti-aliasing techniques.  If you don't believe me, or if you don't think that doing something as simple as changing your font can make a big difference on readability, comprehension, and retention, you might want to check out some of these studies (there are some great tips about use of color, capital letters, etc. there too):

Resources
Text Display Readability Work
Contrast Measures for Predicting Text Readability
A Comparison of Popular Online Fonts: Which is Best and When?
Improve the readability of your web pages
Leaf Digital Graphic Design
Best Typefaces for On-screen Readability
Text, Fonts and Readability