Generally as L, the Roman numeral for 50, notably in post-Roman use.

volume (Metric) As l else, since 1979 and now preferably, as L, See litre. Also prefixed variously, as in mL = millilitre. Note that, unique among SI symbols, the initial letter of litre can be expressed officially in upper or lower case, the standard use of lower case for the original metric units being varied to avoid the confusion of lower-case letter l with the digit 1 that has occurred so widely on printed matter. (Since the litre is a derived unit, and derived units generally have upper-case symbols, the use of upper-case L is far from inconsistent.) The alternative technique of adopting italics or some other graphic variation is deprecated.

fundamental constant As L, see Avogadro constant.

luminance Metric-c.g.s. 1920 As L, See lambert.