Editing Johann Heinrich Lambert (section)

===Physics===
Lambert invented the first practical [[hygrometer]].  In 1760, he published a book on photometry, the ''[[Photometria]]''. From the assumption that light travels in straight lines, he showed that illumination was proportional to the strength of the source, inversely proportional to the square of the distance of the illuminated surface and the [[Lambert's cosine law|sine of the angle]] of inclination of the light's direction to that of the surface. These results were supported by experiments involving the visual comparison of illuminations and used for the calculation of illumination. In ''Photometria'' Lambert also cited a law of light absorption, formulated earlier by [[Pierre Bouguer]] he is mistakenly credited for<ref>{{Cite web|url=https://www.britannica.com/biography/Pierre-Bouguer#ref149726|title = Pierre Bouguer &#124; French scientist}}</ref> (the [[Beer–Lambert law]]) and introduced the term ''[[albedo]]''.<ref>{{cite book|last=Mach|first=Ernst|title=The Principles of Physical Optics|publisher=Dover|date=2003|isbn=0-486-49559-0|pages=14–20}}</ref> [[Lambertian reflectance]] is named after him. He wrote a classic work on [[Perspective (visual)|perspective]] and contributed to [[geometrical optics]].

The non-[[SI]] unit of luminance, [[lambert (luminance)|lambert]], is named in recognition of his work in establishing the study of [[photometry (optics)|photometry]]. Lambert was also a pioneer in the development of three-dimensional [[colour models]]. Late in life, he published a description of a triangular colour pyramid (''Farbenpyramide''), which shows a total of 107 colours on six different levels, variously combining red, yellow and blue pigments, and with an increasing amount of white to provide the vertical component.<ref>Lambert, ''Beschreibung einer mit dem Calauschen Wachse ausgemalten Farbenpyramide wo die Mischung jeder Farben aus Weiß und drey Grundfarben angeordnet, dargelegt und derselben Berechnung und vielfacher Gebrauch gewiesen wird'' (Berlin, 1772). On this model, see, for example, Werner Spillmann ed. (2009). ''Farb-Systeme 1611-2007. Farb-Dokumente in der Sammlung Werner Spillmann''. Schwabe, Basel. {{ISBN|978-3-7965-2517-9}}. pp. 24 and 26; William Jervis Jones (2013). ''German Colour Terms: A study in their historical evolution from earliest times to the present''. John Benjamins, Amsterdam & Philadelphia. {{ISBN|978-90-272-4610-3}}. pp. 218–222.</ref> His investigations were built on the earlier theoretical proposals of [[Tobias Mayer]], greatly extending these early ideas.<ref>Sarah Lowengard (2006) [http://www.gutenberg-e.org/lowengard/A_Chap03.html "Number, Order, Form: Color Systems and Systematization"] and [http://www.gutenberg-e.org/lowengard/glossShell.html?l#l03 Johann Heinrich Lambert] in ''The Creation of Color in Eighteenth-Century Europe'', [[Columbia University Press]]</ref> Lambert was assisted in this project by the court painter [[Benjamin Calau]].<ref>Introduction to {{cite book|date=2011|title=Johann Heinrich Lambert's ''Farbenpyramide''|type=Translation of "Beschreibung einer mit dem Calauischen Wachse ausgemalten Farbenpyramide" ("Description of a colour pyramid painted with Calau's wax"), 1772, with an introduction by Rolf Kuehni|url=http://www.iscc.org/pdf/LambertFarbenpyramide.pdf|url-status=dead|archive-url=https://web.archive.org/web/20160304034654/http://www.iscc.org/pdf/LambertFarbenpyramide.pdf|archive-date=2016-03-04}}</ref>