Editing Kruithof curve (section)

{{Short description|Region of color temperatures that are often viewed as pleasing to an observer}}
{{Use American English|date=March 2021}}
{{Use mdy dates|date=March 2021}}
[[Image:Kruithof curve 2.svg|right|400px|thumb|The Kruithof curve, with an example light source; [[CIE Standard Illuminant D65|D65]] (Northern [[daylight]]), inside the pleasing region.<ref>{{Cite journal|url=http://palimpsest.stanford.edu/waac/wn/wn21/wn21-3/wn21-308.html|title=The Color of White: Is there a "preferred" color temperature for the exhibition of works of art?|date=September 2000|volume=21|issue=3|first=Steven|last=Weintraub|journal=Western Association for Art Conservation Newsletter}}</ref>]]

The '''Kruithof curve''' describes a region of [[illuminance]] levels and [[color temperature]]s that are often viewed as comfortable or pleasing to an observer. The curve was constructed from [[Psychophysics|psychophysical]] data collected by Dutch physicist [[Arie Andries Kruithof]],<ref>{{Cite web|first=Arie Andries|last=Kruithof|url=http://dap.library.uu.nl/cgi-bin/dap/dap?diss_id=7789|title=Aanslag van het waterstofmolecuulspectrum door electronen|date=December 12, 1934|access-date=May 6, 2008|archive-date=July 24, 2011|archive-url=https://web.archive.org/web/20110724171918/http://dap.library.uu.nl/cgi-bin/dap/dap?diss_id=7789|url-status=dead}} (PhD dissertation at [[Utrecht University]] under [[Leonard Ornstein]]) {{in lang|nl}}</ref> though the original experimental data is not present on the curve itself. Lighting conditions within the bounded region were [[Empirical evidence|empirically]] assessed as being pleasing or natural, whereas conditions outside the region were considered uncomfortable, displeasing or unnatural.<ref name=Kruithof1941>{{Cite journal|last=Kruithof|first=Arie Andries|title=Tubular Luminescence Lamps for General Illumination |journal=Philips Technical Review| volume=6|issue=3|pages=65–96|year=1941|issn=0031-7926}}</ref> The Kruithof curve is a sufficient model for describing [[Light#Light source|sources]] that are considered [[Sunlight|natural]] or closely resemble [[Planck's law|Planckian]] [[black body|black bodies]], but its value in describing human preference has been consistently questioned by further studies on interior lighting.<ref name="Davis & Ginthner 1990"/><ref name="Boyce & Cuttle 1990"/>

For example, natural daylight has a color temperature of 6500 [[Kelvin|K]] and an illuminance of about 10<sup>4</sup> to 10<sup>5</sup> [[lux]].{{Citation needed|date=February 2025}} This color temperature–illuminance pair results in natural [[Color Rendering Index|color rendition]], but if viewed at a low illuminance, would appear bluish. At typical indoor office illuminance levels of about 400 lux,{{Citation needed|date=February 2025}} pleasing color temperatures are lower (between 3000 and 6000 K), and at typical home illuminance levels of about 75 lux,{{Citation needed|date=February 2025}} pleasing color temperatures are even lower (between 2400 and 2700 K). These color temperature-illuminance pairs are often achieved with [[Fluorescent lamp|fluorescent]] and [[Incandescent light bulb|incandescent sources]], respectively. The pleasing region of the curve contains color temperatures and illuminance levels comparable to naturally lit environments.