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The Lambda logo (λ) is a symbol found frequently in the Half-Life universe. It represents the Greek letter "Λ" (lowercase "λ"), and is a radioactive decay constant used in the half-life equation. "Λ" is the 11th letter in the Greek alphabet.
Half-Life story arc
In the original Half-Life, Gordon Freeman's trademark HEV Suit was marked with a Lambda Logo on the chest, as were other HEV Suits. A section of Black Mesa dedicated to teleport research was also called the "Lambda Complex," and is identifiable by the Lambda logo at its entrance.
Half-Life 2 story arc
Gordon's Lambda logo on his suit and the work of the Lambda Complex became something of a legendary trademark symbol for the Resistance against the Combine, referring to the acts of Gordon Freeman during the Black Mesa Incident. The rebeles would spray-paint it near supply caches, and resistance bases and safehouses such as White Forest, Black Mesa East, and Kleiner's Lab. Resistance fighters also wear the symbol on their arm bands. They are also used to identify Resistance-friendly Combine weapons such as Hopper Mines and Sentry Turrets, seen by the spray-paint on them.
The Lambda logo can be seen on certain vehicles, such as the orange van that Dog throws to the Citadel in Episode One although any van-type vehicle, regardless of color, has a Lambda logo under the right tail-light. It is also seen in graffiti and propaganda posters across City 17. Dog sports it in his back. A huge Lambda logo can also be found on the rocket hatch and a smaller one on the button used to launch it at White Forest.
- The Lambda is used in the half-life equation to represent the decay constant (i.e. the rate of radioactive decay in an element).
- The Lambda is also used to denote the wavelength of a sound or light emission.
- Lambda is used in some programming languages and parts of math to denote a function.
- The Lambda logo can be found as an Easter Egg in both Left 4 Dead games. In Left 4 Dead Francis has it shaved into his hair. In Left 4 Dead 2, a Charger zombie is seen hanging from posts in a pose exactly like the lambda logo.