THERE WAS A REASON WHY OLD COMPUTERS SHOWED GREEN TEXT HERE’S THEM

Old computers showed green text for a reason: here’s what happened
Green letters on a black background are one of the most recognizable symbols of computer technology in the 1970s and 1980s.
Green letters on a black background are one of the most recognizable symbols of computer technology from the 1970s and 1980s. They appear in old films, retro games, and science fiction. However, the green color wasn’t chosen simply for its distinctive appearance—it had practical advantages.

As SlashGear explains , the main reason was the nature of cathode-ray tube (CRT) monitors. Unlike modern OLED panels, CRTs contained an electron gun that directed an invisible beam onto the inner surface of the glass screen. This was coated with a thin layer of phosphor—a substance that glows when exposed to electrons.

When electrons struck the coating, they transferred energy to its atoms or crystalline structure. The electrons within the material transitioned to a higher-energy state, and upon returning to their original state, they released some of their energy as photons. It was this glow that formed the image on the screen.
The color of the glow depended on the composition of the phosphor. To produce green text, P31—zinc sulfide activated by copper—was used. It produced a yellowish-green glow, corresponding to the range to which the human eye is particularly sensitive. During daytime vision, the eye’s maximum sensitivity is approximately 555 nanometers—specifically, the yellow-green region of the spectrum.
This ensured that the green text appeared bright and high-contrast even with a relatively low electron beam current. Furthermore, the reduced current helped keep the beam narrow and well-focused.

The result was crisp dots and distinct symbols on the screen. In the 1980s, interfaces mostly consisted of letters, numbers, and blinking cursors, so clarity was more important than a rich color palette.

Why did you choose green?
Green wasn’t the only option for monochrome monitors, but the P31 phosphor combined several useful properties. A 1981 Hewlett-Packard catalog called it “probably the best all-around option for refresh rates up to 50 Hz.” The manufacturer praised its luminescence efficiency and resistance to burn-in—qualities especially important for screens that could display the same characters for hours.

Burn-in was a serious problem with CRT monitors. If the image remained static for a long time, individual sections of the phosphor coating would wear unevenly. This resulted in permanent traces of the interface or text appearing on the screen. The P31’s resistance to such damage made it a practical choice for work terminals.
Manufacturers also had to consider the phosphor’s afterglow duration. If it was too short, the image could flicker noticeably. If it was too long, moving characters would leave trails. Green coatings allowed for the right balance between brightness, clarity, and display smoothness.

By the late 1980s, the need for green monitors began to gradually decline. Color screens were becoming more affordable, computer graphics capabilities were expanding, and games, desktop publishing systems, and graphical interfaces required displaying more colors.
Nevertheless, monochrome terminals remained in use for a long time in offices, trading systems, and other industries. Today, glowing green letters are more often found in retro games and films about futuristic technology, reminiscent of what computers looked like at the dawn of personal computing.

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