In the early 1970s, graphic designer Tom Doerr selected the Greek letter lambda to be the symbol of the New York chapter of the Gay Activists Alliance. The alliance's literature states that Doerr chose the symbol specifically for its denotative meaning in the context of chemistry and physics: "a complete exchange of energy–that moment or span of time witness to absolute activity". Within the STEM field, the lambda symbol is associated with the half-life parameter of exponential random variables, which describes the time it takes for a state to change.
In December 1974, the lambda was officially declared the international symbol for gay and lesbian rights by the International Gay Rights Congress in Edinburgh, Scotland. The gay rights organization Lambda Legal and the American Lambda Literary Foundation derive their names from this symbol.