Radiometers are now commonly sold worldwide as a novelty ornament; needing no batteries, but only light to get the vanes to turn. They come in various forms, such as the one pictured, and are often used in science museums to illustrate "radiation pressure" – a scientific principle that they do not in fact demonstrate. The effect begins to be observed at partial vacuum pressures of several hundred pascals (or several torrs), reaches a peak at around 1 pascal (0.0075 torrs) and has disappeared by the time the vacuum reaches 1 ×10 −4 pascals (7.5 ×10 −7 torrs) ( see explanations note 1). At these very high vacuums the effect of photon radiation pressure on the vanes can be observed in very sensitive apparatus (see Nichols radiometer), but this is insufficient to cause rotation.

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a b c Kraftmakher, Yaakov (29 August 2014). Experiments and demonstrations in physics (2ed.). Singapore: World Scientific. p.179. ISBN 9789814434904.Ohio, The University of Akron. "the radiometer using inquiry to teach energy conversions". The University of Akron, Ohio . Retrieved 10 October 2021.

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Wolfe, David; Larraza, Andres (2016). Alejandro Garcia. "A Horizontal Vane Radiometer: Experiment, Theory, and Simulation". Physics of Fluids. 28 (3): 037103. arXiv: 1512.02590. Bibcode: 2016PhFl...28c7103W. doi: 10.1063/1.4943543. S2CID 119235032. When exposed to sunlight, artificial light, or infrared radiation (even the heat of a hand nearby can be enough), the vanes turn with no apparent motive power, the dark sides retreating from the radiation source and the light sides advancing. It was invented in 1873 by the chemist Sir William Crookes as the by-product of some chemical research. In the course of very accurate quantitative chemical work, he was weighing samples in a partially evacuated chamber to reduce the effect of air currents, and noticed the weighings were disturbed when sunlight shone on the balance. Investigating this effect, he created the device named after him.

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Maxwell, J. Clerk (1 January 1879). "On stresses in rarefied gases arising from inequalities of temperature". Philosophical Transactions of the Royal Society of London. 170: 231–256. doi: 10.1098/rstl.1879.0067.

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Reynolds, Osborne (1 January 1879). "On certain dimensional properties of matter in the gaseous state …". Philosophical Transactions of the Royal Society of London. 170: 727–845. doi: 10.1098/rstl.1879.0078. ; Part 2.

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Loeb, Leonard B. (1934) The Kinetic Theory of Gases (2nd Edition);McGraw-Hill Book Company; pp 353–386 Crookes, William (1 January 1874). "On Attraction and Repulsion Resulting from Radiation". Philosophical Transactions of the Royal Society of London. 164: 501–527. doi: 10.1098/rstl.1874.0015. S2CID 110306977. .

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a b c Gibbs, Philip (1996). "How does a light-mill work?". math.ucr.edu/home/baez/physics/index.html. Usenet Physics FAQ . Retrieved 8 August 2014. Worrall, J. (1982). "The pressure of light: The strange case of the vacillating 'crucial experiment' ". Studies in History and Philosophy of Science. 13 (2): 133–171. Bibcode: 1982SHPSA..13..133W. doi: 10.1016/0039-3681(82)90023-1. US 182172,Crookes, William,"Improvement in Apparatus For Indicating The Intensity of Radiation",published 1876-09-12 Han, Li-Hsin; Shaomin Wu; J. Christopher Condit; Nate J. Kemp; Thomas E. Milner; Marc D. Feldman; Shaochen Chen (2010). "Light-Powered Micromotor Driven by Geometry-Assisted, Asymmetric Photon-heating and Subsequent Gas Convection". Applied Physics Letters. 96 (21): 213509(1–3). Bibcode: 2010ApPhL..96u3509H. doi: 10.1063/1.3431741. Archived from the original on 22 July 2011.Brush, S. G.; Everitt, C. W. F. (1969). "Maxwell, Osborne Reynolds, and the Radiometer". Historical Studies in the Physical Sciences. 1: 105–125. doi: 10.2307/27757296. JSTOR 27757296. Thermodynamic explanation [ edit ] A Crookes radiometer in action with the light switched on and off. (Note that the explanation given in the caption to the clip doesn't agree with the modern explanation.) Movement with absorption [ edit ] Calaprice, Alice; etal. (27 October 2015). An Einstein encyclopedia. Princeton University Press. p.190. ISBN 978-0691141749.