HMI Design - Don't Use ALL CAPS!

Many engineers have been taught in drafting classes that WRITING IN ALL CAPS CUTS DOWN ON COMMUNICATION ERRORS.  As a result, it is very common to find HMI screens (and PLC programming, but that is a different topic) that are designed in all caps.  Let's talk about why all caps does not belong on HMI screens.

Word Shapes

Studies have shown that people read uppercase words 10-15% slower than other texts.  Many experts believe it has to do with how uppercase affects word shape recognition.  When we read, we don't actually read letter-by-letter, do you remember this email chain from several years ago?

Aoccdrnig to a rscheearch at Cmabrigde Uinervtisy, it deosn’t mttaer in waht oredr the ltteers in a wrod are, the olny iprmoatnt tihng is taht the frist and lsat ltteers be at the rghit pclae. The rset can be a toatl mses and you can sitll raed it wouthit porbelm. Tihs is bcuseae the huamn mnid deos not raed ervey lteter by istlef, but the wrod as a wlohe.

This email demonstrates that readers don't actually digest individual letters.  More often, readers are actually using the shape of words to help read.  This is what makes all caps writing harder to read.  When text is in all caps, every word is a rectangle, which forces readers to read letter-by-letter, reducing reading speed.

 Word shape affects reading speed.

Word shape affects reading speed.

Sentence Case & Title Case

Sentence case and title case are both better alternatives to all caps.  Sentence case is when only the first letter in a sentence is capitalized.  For example: "Writing in all caps is hard to read."  Title case is when the first letter of every word is capitalized.  Example: "Writing In All Caps Is Hard To Read."  Both styles work well on HMI screens, the key is to be consistent. 

In addition to being easier to read, title case and sentence case both take up less room than all caps.  Who doesn't want more real estate?!

 Which buttons would you prefer to use to operate the conveyors?

Which buttons would you prefer to use to operate the conveyors?

Is it ever okay to use all caps?

Yes.  All caps are fine in contexts that don't involve much reading, such as logos, headings, acronyms, and abbreviations.


Don't develop HMI screens in all caps, is is slow and hard to read.  Developing in sentence case or title case is much better!