Back in the day when mainframe computers grinded away for hours or days processing what, by today’s standards, is relatively small amounts of data, lights blinked and flashed on the computer face. These indicators intended to help operators understand the mysterious interworking of the machine were nearly unintelligible, but pretty to look at. Humorous labels and placards (often in a fake German-like English) about the “blinkenlights” found their way onto many mainframes during the 1950s and 1960s, and the moniker is still in use by some computer geeks and hackers today.
Although joked about in some circles, blinking information is an essential part of many human-machine systems, and their design and use in warning systems and alerts is no laughing matter. A pilot faced with a mechanical problem, a medical technician operating an electrocardiogram, or just you or I driving our car down the road are dependant upon well designed, discernible, and correctly timed information that is critical to the safety of ourselves and others. Blinking grabs our attention, conveys urgency, and differentiates the information being presented.
Blinking, that is the display of information that alternates between two states (on/off, bold/ non-bold, normal text/reverse video), is commonly used as either highlighting or coding. Highlighting is the practice of making a display or display element more distinguishable by presenting it in a way that is different from other display elements, while coding assigns meaning to design characteristics to represent information in short form. The word flashing is often used interchangeably with blinking.
If used sparingly, blinking can be an effective way to quickly attract attention. However, its overuse can also impair performance. So, the use of blinking in display design needs to be carefully considered. Here are a few tips on how to use blinking effectively.
• Use blinking to attract attention
Minimal amounts of blinking can effectively attract attention in the following situations: when a hazardous condition or malfunction occurs, when immediate intervention is required, when the operator’s eyes are likely to be elsewhere, when a new condition occurs, when there is a high priority task requiring attention, or when compensating for a lack of color on a monochrome display.
• Use blinking to make information distinct
Blinking signal lights are detected more quickly than steady signals when all other lights are steady. Many sources state that when using blink codes, fewer than half of the background lights should flash at a given time. However, blinking text can be difficult to read. Avoid blinking text that for words that are intended to be read, as opposed to text that is just meant to be recognized. If blinking text is used, it should flash between full and half intensity.
• Avoid blinking that is annoying or lacking meaningful information
Indiscriminate use of blinking can be annoying, and inappropriate highlighting or coding can cause user complaints, frustration, or annoyance. To avoid blinking that is annoying do not use it too often, for inappropriate or unnecessary operations, or for too long of a duration. If a signal is repeated often in the absence of meaningful information, users will learn to ignore the signal.
• Avoid blinking that causes fatigue
Blinking as well as several other display characteristics may contribute to eye fatigue if used excessively (others include brightness coding, patterns or complex graphics, color coding, and reverse video). To help prevent fatigue do not use more than two levels of blink coding, such as a slow flash and a fast flash, and also allow the user to terminate the blinking.
• Be clear and consistent in the use of blinking
The meaning of blink coding should be clear and consistent. For example, blinking should not mean caution for one parameter and warning for another. Blinking should also be used consistently for all other related controls and displays.
• Assess the impact of blinking on other displays and controls
Blinking displays should not inappropriately distract from other displays. If multiple blinking displays must be active at the same time, the blinking rates should be synchronized.
• Use the right blink rate and duty cycle
Blink rate is the number of blinks over a given time. Blink rates are typically expressed in cycles per second, or Hertz. Different rates convey different information, and what is the right rate will vary by application. Consult your industry standards and engineering guidelines for the appropriate rates for your product. Duty cycle is the ratio of the “on” period to the total cycle. A duty cycle of 50% is commonly recommended.
For detailed information on human factors considerations for the use of blinking in general, and in the specific application to flight deck controls, check out the HFYI Design CoPilot™ at http://www.designcopilot.com/. A product of Research Integrations, HFYI Design CoPilot™ lists 13 human factors considerations for blinking regarding controls, displays, systems and testing assumptions. It also provides information from FAA regulations and guidance materials, as well as industry standards documents from ARINC, RTCA, SAE, and GAMA.