Nixie Tubes, Split-Flap Boards and Seven-Segment Displays: A Short History of Number Faces
Almost every way of showing a number that we now think of as “retro” was, at the time, a hard engineering problem solved with whatever technology was available: neon gas, printed plastic flaps, glowing phosphor, or a handful of light-emitting diodes. Each solution left a distinct visual signature, and those signatures are what people are choosing when they pick a nixie or split-flap face for a clock or a counter today.
Here is a short tour of where the main ones came from.
The nixie tube (1950s)
A nixie tube is a glass bulb filled with neon at low pressure. Inside are ten thin metal cathodes, each shaped like a digit, stacked one in front of the other, with a mesh anode around them. Apply voltage to one cathode and the neon around it glows orange, so that digit lights up while the others stay dark behind it.
Burroughs Corporation introduced the design commercially in the mid-1950s. The name comes from an internal label, “NIX I”, for Numeric Indicator eXperimental. Through the 1960s nixies were the standard readout on laboratory instruments, frequency counters and early desktop calculators.
What people love about them now is the depth. Because the digits are physically stacked, the lit one sits at a slightly different distance from the glass than its neighbours, and the unlit cathodes are faintly visible around it. A good nixie rendering keeps those ghost digits. The warm orange comes from neon itself; there is no phosphor involved.
They were displaced by LED and vacuum-fluorescent displays, which were cheaper and easier to drive, and survive today in small-batch clocks.
The split-flap board (1950s onward)
A split-flap display shows a character on a stack of printed flaps that rotate on a drum. Each flap is split horizontally; as the drum turns, the top half falls forward to reveal the next character. The clatter of a whole board updating is the sound of railway stations and airports for many people.
The Italian company Solari di Udine developed and popularised the mechanism in the 1950s, and their boards spread through stations and airports worldwide. Solari also made flip clocks for the home; Gino Valle’s Cifra series from the 1960s is now a design-museum object.
The visual grammar is unmistakable: a horizontal line through the middle of every character, slightly rounded flap corners, a shadow under the top flap. Digital recreations that skip the split line tend to look like ordinary type in a box; the line is the whole point.
The seven-segment display (1908, popular from the 1970s)
The idea of building every digit from seven bars in a figure-eight arrangement is older than most people expect. A patent for it was filed in 1908 in the United States. But it needed a light source that could be made small and cheap before it became practical.
That source arrived with the light-emitting diode. In the early 1970s, LED seven-segment displays appeared in pocket calculators and the first digital wristwatches, glowing red because red was the colour early LEDs could produce efficiently. Later in the decade, liquid crystal versions arrived, which drew almost no power and made the always-on digital watch possible. LCD seven-segment digits are usually dark on a grey-green field, with the unlit segments faintly visible, which is why “LCD” and “seven-segment” faces look different despite sharing a geometry.
The distinctive quirks are the italic lean many displays use, the small gaps between segments, and the fact that 6, 7 and 9 can each be drawn two ways.
The phosphor terminal (1970s and 1980s)
Before flat panels, a computer terminal was a cathode-ray tube. An electron beam scanned across a phosphor coating, line by line, and the phosphor glowed where it was hit. The colour depended on the phosphor: green was the most common, amber came next, and white later.
Three artefacts define the look. Scanlines, because the beam draws in horizontal rows with dark gaps between them. Bloom, because a bright glyph bleeds light into the glass around it. And persistence, because the phosphor keeps glowing briefly after the beam moves on, leaving faint trails on moving text. Crisp edges with no glow do not read as a CRT, however green.
The dot matrix (1960s onward)
A dot matrix shows characters on a grid of dots, classically five wide by seven tall. It appeared in LED form on instruments and signage, as flip-dots on bus destination signs, and, most famously, in impact printers. The grid gives every glyph the same chunky shape, and designers have been drawing type inside it for sixty years.
Why these still work on a phone
Each of these displays solved the same problem, showing a number, with a different physical constraint, and the constraint is what gives each its character. A phone screen has no such constraints, which is exactly why borrowing them is appealing: the constraints are now a style choice.
TimeBorn’s face catalogue includes drawn-from-scratch versions of all of these: a nixie tube with its ghost cathodes, split-flap and flip-deck faces with the centre line and shadow, LCD and LED seven-segment styles, a phosphor CRT with scanlines and bloom, and a dot matrix. They are vector, not screenshots, so they stay sharp at any size, and you can see every one of them on your own wallpaper photo before choosing. Take a look on the home page.