Concept and visual structure

A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the Hindu-Arabic numerals. Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays.
The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumeric); however, these have mostly been replaced by dot-matrix displays.
Often the seven segments are arranged in an oblique, or italic, arrangement, which aids readability.

A mechanical seven segment display for displaying petrol prices.
Most separate 7-segment displays use an array of light-emitting diodes (LEDs), though other types exist using alternative technologies such as cold cathode gas discharge, vacuum fluorescent, incandescent filament, liquid crystal display (LCD), etc. For gas price totems and other large signs, electromagnetically flipped light-reflecting segments (sometimes called "vanes") are still commonly used. An alternative to the 7-segment display in the 1950s through the 1970s was the vacuum tube-like nixie tube.
In a simple LED package, each LED is typically connected with one terminal to its own pin on the outside of the package and the other LED terminal connected in common with all other LEDs in the device and brought out to a shared pin. This shared pin will then make up all of the cathodes (negative terminals) OR all of the anodes (positive terminals) of the LEDs in the device; and so will be either a "Common Cathode" or "Common Anode" device depending how it is constructed. Hence a 7 segment plus DP package will only require nine pins to be present and connected.Integrated displays also exist, with single or multiple digits. Some of these integrated displays incorporate their own internal decoder, though most do not – each individual LED is brought out to a connecting pin as described



Seven segment displays can be found in patents as early as 1908 (in U.S. Patent 974,943, F W Wood invented an 8-segment display, which displayed the number 4 using a diagonal bar), but did not achieve widespread use until the advent of LEDs in the 1970s. They are sometimes even used in unsophisticated displays like cardboard "For sale" signs, where the user either applies color to pre-printed segments, or (spray)paints color through a seven-segment digit template, to compose figures such as product prices or telephone numbers.For many applications, dot-matrix LCDs have largely superseded LED displays, though even in LCDs 7-segment displays are very common. Unlike LEDs, the shapes of elements in an LCD panel are arbitrary since they are formed on the display by a kind of printing process. In contrast, the shapes of LED segments tend to be simple rectangles, reflecting the fact that they have to be physically moulded to shape, which makes it difficult to form more complex shapes than the segments of 7-segment displays. However, the high common recognition factor of 7-segment displays, and the comparatively high visual contrast obtained by such displays relative to dot-matrix digits, makes seven-segment multiple-digit LCD screens very common on basic calculators