Johann Heinrich Lambert (26.08.1728-25.09.1777) was a German scientist and a member of the Berlin Academy of Sciences (1765). He was born in Mulhouse.
His research in physics was in the field of photometry, thermal conductivity, hygrometry and other subjects. In 1760 his fundamental work “Photometry, or On the Measurement and Comparison of Light, Colours and Shadows” appeared, and it was of great importance for optics. In it Lambert in effect established the basic concepts of photometry (luminous intensity, luminance and illuminance) and a number of photometric regularities, in particular that illuminance is inversely proportional to the square of the distance and directly proportional to the sine of the angle made by the light rays with the illuminated surface. The same work contains his law of the absorption of light by a medium, which had originally been established in 1729 by P. Bouguer (the Bouguer–Lambert law). In his work “Pyrometry”, published posthumously in 1779, he described experiments on thermal radiation, considered the propagation of heat along a rod and showed that heat rays, like light rays, travel in straight lines and that their intensity varies inversely with the square of the distance. He regarded quantity of heat and temperature as different concepts (1755). He studied the thermal expansion of air, the refraction of light in the atmosphere and other questions. His work also concerned mathematics and astronomy; in particular, his cosmogonical views were close to those of I. Kant. He put forward the idea of a hierarchical structure of the Universe [254, 405, 557].