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Why Choose Color Displays?

Medical Device & Diagnostic Industry
Magazine

MDDI Article Index

Originally published October 1996

Michael Wiklund and William Dolan

There is an entire class of medical devices, such as infusion pumps, blood gas analyzers, and ventilators, that could be considered technological centaurs—part mechanical device and part computer. Intermixing mechanical and computer components has greatly extended the functionality of these devices over the past decade, enabling physicians to develop entirely new therapy regimes. It has also led to a shift in the way people interact with those products. Information display and control actions previously assigned to dedicated-purpose meters, counters, knobs, and switches are now handled via interactions with software. The ubiquitous control panel has been replaced with the increasingly ubiquitous computer display and input device, such as a trackball or arrow keys. Turning a knob has been replaced by "highlighting and selecting."

Initially, these centaurlike products incorporated very small displays; typically a 2-line by 16-character liquid crystal display (LCD) or its equivalent. These little displays had considerable value, but also introduced significant usability problems. Comparing interactions with a medical product to a person-to-person conversation, the little displays made conversation overly terse, leading to miscommunication. Because of the lack of screen titles and meaningful prompts, device users found themselves confused about their place in a sequence of tasks, unsure of the meaning of terms abbreviated to fit the available space, and puzzled about the next step of a task.

Fortunately, as soon as prices came down, manufacturers started to incorporate larger displays to resolve, among other things, usability problems. The displays of choice over the past couple of years have been the full-size (640×480-pixel) VGA monochrome electroluminescent panel or LCD and their quarter-size cousins (320×240 pixels) that are cut from the full-size glass pieces. These displays have become relatively inexpensive and widely available, largely because of their extensive use in notebook computers.

Now, many manufacturers are pondering the same next step that the computer laptop industry has already taken: upgrading to color. An upgrade to color has considerable allure. Color certainly enriches communications between user and device, boosting a device's usability and desirability. For example, end-users state a strong preference for color-coded warning messages (e.g., white text on a red banner to indicate a dangerous condition), which can be very attention getting and start communicating their message (i.e., there is a problem) upon initial glance. These benefits of color have already been proven in higher-end products, such as integrated patient monitors and advanced imaging devices that are clearly special-purpose computers. But the considerable difference in price between monochrome and color displays is still a concern to manufacturers of lower-cost medical devices, the aforementioned centaurs. Consequently, design decisions regarding the use of a color versus monochrome display often stall and become the subject of endless debate and waffling.

THE ADVANTAGES OF COLOR

Recognizing that others will champion the cause of low-cost monochrome displays (see sidebar), the balance of this article offers arguments in favor of stepping up to color. Some of the arguments may be familiar ones, but others may not. The number of advantages offered by color versus monochrome displays may be surprising.

Image Quality. Image quality varies widely between and within general classes of displays, including cathode ray tubes (CRTs), electroluminescent panels (ELPs), vacuum fluorescent displays, and LCDs. Although there are exceptions to the general rule, image quality increases as display cost increases. For example, a monochrome LCD (twisted nematic/passive matrix) is relatively inexpensive, but has several image quality shortcomings. Such displays are not as bright as others, are prone to viewing-angle limitations, and refresh slowly, blurring dynamic effects such as cursor movement or list scrolling. By comparison, a color LCD (thin-film transistor/active matrix) provides a reasonably bright image that refreshes quickly and affords a wider viewing cone. It is important to note, however, that some monochrome displays such as CRTs and ELPs also provide high-quality images.

Visual Appeal. As common sense would suggest, people generally regard colored screens as more visually appealing than monochrome screens. Anecdotal remarks and quantitative ratings by participants in user studies consistently reinforce this conclusion. For example, if you conduct a focus group or usability test with prospective customers and show them a version of an information display in color versus monochrome (gray scale), almost all will prefer the color screen. In some sense, this preference is comparable to people's general preference for stereo over monaural sound. Color adds an extra dimension to the visual experience, enabling people to draw upon the full capability of their senses. As such, customers will exhibit a natural attraction to, and preference for, colored displays over monochrome displays, all other things being equal.

Graphic Simplicity. Color monitors afford designers a greater opportunity to produce simple-looking screens. The reason is that adjacent colors of differing hue (spectral wavelength composition) and similar value (lightness versus darkness) create natural borders, whereas adjacent gray tones are incrementally less effective (see Figure 1). As a result, colored elements do not always need edge demarcation to assure distinctiveness, for example, where monochrome screens do. In comparison to colored screens, most monochrome displays are burdened with extra on-screen elements, adding to their visual complexity.

Color Coding. Color is a terrific method of coding important information. When color is not available, one must resort to other coding techniques. Alarm messages, for example, can be made larger and bolder than other text, physically segregated from other information, highlighted by means of demarcation lines or an inverse video effect, or be presented using a symbol (e.g., a bell or horn symbol) in place of text. However, as Figure 2 illustrates, color is a most compelling coding technique when it comes to detecting alarm information embedded within other information. In fact, human factors studies have shown that color outperforms other visual codes, such as size, shape, and brightness as a coding technique.1 It performs particularly well when the task is to search for an item or group of items among many, or to track a moving target.

More Information. Color displays offer the potential to present more information at a time than monochrome displays. As discussed above, it is simply a matter of having one dimension for communicating information. Christopher Goodrich is a senior industrial designer with Ohmeda, Inc. (Madison, WI), a manufacturer of anesthesia delivery systems. He considers a color display essential to the usability of medical devices that present a lot of information in parallel. "Color gives you an effective way to visually separate groups of information so that the information is easier for users to find," he says. "This helps you avoid a trade-off imposed by monochrome screens—putting in less information to avoid visual clutter."

Competitive Advantage. Competing manufacturers often engage in so-called feature wars. In such wars, manufacturers arm their products with extra features (usually software functions that can be enabled or disabled) that appeal to customers initially but rarely get used. As an everyday example, consumers are drawn to CD players that can play songs from several CDs in a preprogrammed sequence, but few use the feature once they own the device. In the medical world, the valued but unused feature might be a special data-analysis feature.

Color displays are different. They provide a continual benefit to users, much the way a good sound system rewards the listener. Color displays also provide a significant competitive advantage, particularly in head-to-head comparisons that take place in clinical environments and trade shows. As many marketing managers can attest, devices equipped with color displays tend to draw more casual interest among people walking the trade-show floor. The competitive advantage can be expected to shift toward products incorporating a monochrome display only when minimum cost is the dominant purchase criteria.

Some companies may consider color displays a necessity only when technology matures and manufacturers start to compete on the basis of design quality as opposed to functional capability. As such, companies holding an initial technological advantage may equip their products with monochrome monitors, expecting to sell just as many units and maximize profit. However, this approach offers future competitors an opportunity to break into the market with a me-too product equipped with a color display, meeting a demand for higher user-interface quality. Therefore, an early commitment to color before it becomes a necessity may be an effective way to ward off future competition while also boosting user-interface quality.

Progressive Image. Medical and diagnostic device manufacturers work hard to establish a positive image for their company in the marketplace. Most seek a progressive image, positioning themselves on the leading edge in terms of technology, perceived quality, and actual quality. It is not clear that marketing a product incorporating a monochrome display will erode a progressive image, but it could. For instance, when customers check out products incorporating monochrome displays for the first time, they are prone to label them old-fashioned or cheap. This perception may be a case of transference from people's experience with black-and-white versus color television. In comparison, the same product equipped with a color display might be labeled as progressive and user-friendly.

Meeting Customer Expectations. Today, such consumer electronics as palmcorders, pocketable TVs, and digital cameras incorporate color displays. This has raised the ante for industrial product manufacturers. Customers are becoming accustomed to high-quality color displays in place of monochrome displays. Therefore, some customers may feel neutral at best about using a product incorporating a monochrome display. However, other customers may regard the product as less user-friendly.

A spokesperson for Aksys, Ltd. (Libertyville, IL), a start-up company developing a system for hemodialysis, agrees that color has a real draw for customers. "Color can raise a customer's perception of product quality and user-friendliness—no question about it. Our customers are certainly used to products in their daily lives, such as televisions and home computers, that use color monitors. Therefore, their in-home experience raises the expectation for color in a medical product intended for use in the home. So, even though competitors might not be forcing us toward color at this time, we have to look seriously at the customer's preference for color."

Goodrich is also convinced that forces outside the medical industry are compelling medical device manufacturers to use color displays. "Customers are starting to expect medical devices to incorporate color displays, largely due to their experience with consumer products. This shift in expectation stands to make monochrome displays obsolete for application to products that require large displays." Speaking for himself and the hundreds of customers he has interviewed, Goodrich adds, "Monochrome displays are just so lacking in overall appeal, you want to avoid them except in cases where the wide-angle viewing capability of ELPs is essential."

Future Enhancement. In the near future, the struggle of choosing between color and monochrome displays should end. The cost differential will shrink and color displays will be the de facto standard for high-tech devices. Accordingly, the late 1990s represents a transition period, posing a shelf-life problem for manufacturers that choose monochrome for their next-generation products. What are manufacturers going to do when the marketplace forces them to upgrade to color? For many, the hardware needed to support a monochrome display will not support an upgrade without major redesign and retooling. Display mounts, power supplies, and display controllers may be incompatible, although some manufacturers have started to engineer commonality into their monochrome and color product lines. Also, a subsequent switch to color may require considerable software changes. So, initial reductions in development and manufacturing costs may be counterbalanced by the costs of design changes or introducing yet another next-generation product to market ahead of the intended schedule.

To hedge their bets, manufacturers can take a hybrid approach: designing for monochrome today, allowing for an easy upgrade to color tomorrow. This approach may result in some overengineering at the outset, but is likely to reduce product development and manufacturing costs in the future. Overengineering may come in the form of a flexible approach to display mounting and higher-capacity display drivers, for example. It may also come in the form of extra software code with setup functions that enable the appropriate code to produce a monochrome versus color image. However, it is possible to develop a single version of the software that works with either a color or monochrome monitor. The effect is akin to starting with a color monitor and adjusting the colors so that everything looks monochromatic. Making this approach work requires care in picking colors of equivalent value (lightness versus darkness) so that the monochromatic image has a consistent appearance.

Customer Choice. Rather than making a display decision, some manufacturers offer both color and monochrome displays and let customers decide between them. The extra costs of engineering and manufacturing both types of units can be recovered by marking up the color units, for example, presuming that some customers will pay the extra amount. Then, as the cost of color displays decreases to meet the cost of monochrome displays (due to economies of scale and competition), the monochrome monitor can be dropped from the inventory. From the beginning, this approach pays off in terms of establishing a high-tech image while also being able to offer a reduced price on an entry-level product. Typically, this approach requires designers to introduce redundant information coding, augmenting a color code with some other coding technique, such as shape-coding or size-coding. This ensures that a colored screen will still work in monochrome. Redundant coding also benefits people who have impaired color vision (8–10% of Caucasian males, about 4% of non-Caucasian males, and about 0.5% of all females).2

Avoiding Supply Problems. Already, there is concern over the availability of monochrome monitors in the future. Many manufacturers wonder if they will face a problem similar to finding low-end microprocessors (i.e., 286 chips) in a market that has moved on to higher-powered microprocessors (i.e., 486 chips). In fact, small monochrome CRTs are approaching the obsolescence point. However, those that choose color today face a potential problem that stems from volatility in the notebook computer market. Specifically, color display manufacturers are likely to adjust their product lines according to the needs of their dominant buyers—notebook computer manufacturers. In the near future, this may lead some manufacturers to abandon 10.4-in. diagonal displays, for example, in favor of larger ones. This potential reinforces the need for medical device manufacturers to engineer flexibility into both their products and manufacturing processes.

Device Integration. Many medical devices are used in conjunction with others. This is particularly true of devices used in the operating room and intensive-care environments. Such environments are not known for high levels of integration between products. However, there is a growing trend toward integration. For example, anesthesia workstations used to be a conglomerate of devices placed on various shelves. Now, companies are working together to produce integrated solutions. If one extrapolates this trend, one can envision entire systems of components that work together, sharing data and control capabilities. Products equipped with color displays fit well with this vision of high-quality user interactions with technology. By contrast, products equipped with monochrome displays may be viewed as impoverished relative to other, higher-end devices.

Third-Party Applications. With the advent of medical information highways within hospitals, many products will be sharing information. As a result, displays previously dedicated to a specific function, such as presenting vital signs and waveforms, may also display laboratory results and E-mail. In such cases, the use of a color display will be essential to ensure that third-party applications look correct.

Economies of Scale. Because of the costs involved, equipping certain lower-end products that have limited user-interface requirements with color monitors may be viewed as overkill as well as detrimental to sales. However, companies that also market higher-end products equipped with color displays may discover economies of scale favoring across-the-board use of color displays. The economies may not accrue strictly on cost of goods. Rather, they may accrue from reduced inventory, engineering, servicing, and software development costs.

CONCLUSION

Applications for monochrome monitors remain. However, for those manufacturers weighing the trade-offs between color and monochrome displays, there are abundant reasons to select color. Presuming a professional application of color in screen design, a color display opens up new dimensions in user-interface design that enhance a product's overall usability and appeal. Still, the added dimension of color may pale in comparison to the benefit of minimizing the cost of a product that must compete in a price-sensitive market. This trade-off is what makes the decision between color and monochrome displays so difficult.

For some product manufacturers, the cost considerations may lead to the continued use of monochrome displays for a few more years while the cost of color displays continues to drop. However, individuals calculating the benefits and costs should take care to consider all of the potential benefits of color that extend beyond the visual appeal of a given product or even the economics of a single product line. Moreover, decision makers should ask themselves the pointed question: Which type of display would I choose if I had to look at it every day for many years? Chances are that the very same individuals use a desktop computer equipped with a color display.

REFERENCES

1. Thorell LG, and Smith WJ, Using Computer Color Effectively—An Illustrated Reference, Englewood Cliffs, NJ, Prentice-Hall, p 7, 1990.

2. Thorell LG, and Smith WJ, Using Computer Color Effectively—An Illustrated Reference, Englewood Cliffs, NJ, Prentice-Hall, p 117, 1990.


Michael Wiklund directs the Usability Engineering Group and William Dolan serves as Usability Test Laboratory manager at American Institutes for Research (Lexington, MA), which provides user-interface design consulting services to manufacturers of medical, scientific, and consumer products.


Figure 1. Differentiating graphical elements using color versus line.

Figure 2. Using color to highlight critical information.


COUNTERPOINT: ADVANTAGES OF MONOCHROME DISPLAYS

Some of the advantages of using monochrome displays are listed below. As is the case with any product or component, it's up to the manufacturers to decide what's best for their companies and customers.

  • Lower display cost.
  • Lower cost of associated hardware (controller, power supply, microprocessor).
  • Simplified software coding (depending on the nature of graphical elements).
  • Wider viewing angles (depending on the technology).
  • Established technologies (e.g., LCDs, CRTs, ELPs) that are less subject to rapid change.
  • Longer display life cycle (certain technologies).
  • Appearance of design frugality in the eyes of price-sensitive customers.
  • Subdued appearance that may not be as distracting to patients.


SAMPLE DISPLAY COSTS

The relatively low cost of monochrome displays is often what keeps manufacturers from changing to higher-priced color displays. Following is a cost comparison.

Monochrome LCDs $200–$250
Monochrome ELPs $300–$400
Color TFT (active matrix) $600–$900

Source: Cost data shared by established medical device manufacturers that have performed benefit-to-cost analysis of VGA display alternatives.


USING COLOR TO COMMUNICATE BETTER

Information displayed on-screen can be enhanced with the use of color. In many instances, color also allows more information to be presented on-screen. Following are some examples.

  • In a breathing circuit diagram, the lungs can be colored pink, making them more recognizable as a body part as well as indicating proper oxygenation.
  • Bar graphs associated with anesthesia gas flows can be colored to match standards for the labeling of compressed gases (e.g., green for oxygen in the U.S. market).
  • An arterial blood pressure waveform can be colored red to reinforce an association with oxygenated blood.
  • On-screen start and stop buttons can be colored green and red, respectively, to reinforce a traffic light metaphor (i.e., green means "go" and red means "stop").
  • To indicate high priority, important messages can be printed on a yellow, rectangular square to resemble Post-it notes.
  • To help users recognize components, maintenance diagrams can depict the actual appearance of the product using as many colors as necessary or even show a digitized color photograph.

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Copyright© 1996 Medical Device & Diagnostic Industry

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