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Index of Refraction of Air



Jack A. Stone Jr., Jay H. Zimmerman


These Web pages are intended primarily as a computational tool that can be used to calculate the refractive index of air for a given wavelength of light and given atmospheric conditions (air temperature, pressure, and humidity). The calculations are performed using either the Ciddor equation or an updated version of the Edlen equation with a modification of the water vapor term so as to improve accuracy for shop-floor use at temperatures departing substantially from 20 degrees C. The text accompanying the calculations explains our modification of the Edlen water vapor term, provides a tutorial for users of the Web page, and reviews and discusses the relative merits of the two equations, the range of validity, and the estimated uncertainty of the calculations. In addition, the text gives a complete description of all calculations employed by the Web page so that others desiring to reproduce the calculation can do so. Finally, we propose a simplified formula that can be used for shop-floor computations of the refractive index when only a hand calculator is available.
Index of Refraction of Air


air refractive index, Ciddor equation, Edlen equation, index of refraction, interferometry


Stone, J. and Zimmerman, J. (2001), Index of Refraction of Air, Index of Refraction of Air, [online], (Accessed April 19, 2024)
Created February 16, 2001, Updated June 2, 2021