Figure 8-13. The segmentation used by the CST-1 watch. Note the first digit misses unnecessary segments as it will only ever need to display “1” or “2” to display time. Dynamic displays Displays with the fewest limitations have a matrix of pixels each of which can be turned on or off individually. In principle, displays like this are the kind we’re all used to from smartphones or computer monitors. A notable distinction is between monochrome and color displays. Monochrome displays tend to be cheaper, but (as their name suggests) unable to display colors or shades. The Fitbit activity tracker uses such a monochrome OLED matrix display. It shows both alphanumeric information and simple graphics (see figure 8-14).
Figure 8-14. The Fitbit activity tracker uses a monochrome matrix display. UX designers will be familiar with color pixel matrix displays from smartphones, laptops and tablet devices. Touch screens are essentially pixel matrix displays combined with a transparent touch sensitive layer. Electronic ink displays A more unusual display technology with unique advantages and disadvantages is electronic ink. Made popular through eBook readers like Amazon Kindle, the technology is used in more and more devices like connected watches or smartphones. Electronic ink displays resemble the appearance of paper and are easy to read in direct sunlight. Unlike the other technologies described above, they only require electricity to change the state, not to hold it. This means the device uses less power. This opens up new possibilities for designers, too. For example, an electronic ink display can show something when a device is off. To greet and guide users, a display could already show information when the user unpacks the product and hasn't even switched on. There are also some disadvantages that constrain the design. Electronic ink displays have a very low refresh rate. They also suffer from an effect called ‘ghosting’, where shadows from a previous display state can still be seen. This rules out interactions like scrolling, the use of mouse pointers or animations in the UI. Is a screen better than no screen? You might think it’s good to put a screen on a device where possible, but this isn’t necessarily the case. Screens and physical controls increase the cost of a device. They mean extra components and add design and development effort. When designing apps or websites a lot of work has already been done for designers. They can rely on platform features or design frameworks. If you add a screen to a connected device, you essentially need to develop an interaction paradigm from scratch. How do menus work? How do you navigate them? How do users learn the unfamiliar UI?