Lam·bert \ˈläm-ˌbert\ , Johann Heinrich (1728–1777), German mathematician, physicist, and philosopher. Largely self-educated, Lambert investigated geometry and astronomy, doing so by means of instruments which he himself designed and built. He also made significant contributions to the knowledge of heat and light. In 1760 he demonstrated for the first time how to measure quantitatively the intensity of light. The cgs unit of measurement for light intensity, the lambert, is named in his honor.