Photometria

Lambert began with two simple axioms: light travels in a straight line in a uniform medium and rays that cross do not interact.

See: Lambertian reflectance, Lambertian emitter Lambert demonstrated these principles in the only way available at the time: by contriving often ingenious optical arrangements that could make two immediately adjacent luminous fields appear equally bright (something that could only be determined by visual observation) when two physical quantities that produced the two fields were unequal by some specific amount (things that could be directly measured, such as angle or distance).

The forty experiments described in Photometria were conducted by Lambert between 1755 and 1760, after he decided to write a treatise on light measurement.

His interest in acquiring experimental data spanned several fields: optics, thermometry, pyrometry, hydrometry, and magnetics.

He used linear algebra and calculus extensively with matter-of-fact confidence that was uncommon in optical works of the time.

[11] From the references in Photometria and the catalogue of his library auctioned after his death, it is clear that Lambert consulted the optical works of Isaac Newton, Pierre Bouguer, Leonhard Euler, Christiaan Huygens, Robert Smith, and Abraham Gotthelf Kästner.

In Joseph Priestley's survey of optics of 1772, “Lambert’s Photometrie” appears in the list of books not yet procured.

The first appraisal of Photometria appeared in 1776 in Georg Simon Klügel’s German translation of Priestley’s 1772 survey of optics.

[19] Fifty years after that, computer graphics took up Lambert's results as the basis for radiosity calculations required to produce architectural renderings.