Term: dichroism https://doi.org/10.1351/goldbook.DT07357 Definition: Dependence of absorbance of a sample on the type of polarization of the measuring beam. This polarization may be linear, corresponding to linear dichroism (LD) in which the difference in absorption for two perpendicularly linearly polarized beams is measured, ΔAl = AZ - AY, or circular dichroism (CD) in which the difference in absorption for left minus right circularly polarized beams is measured, ΔAC = AL - AR. Related Terms: 1) absorbance (http://doi.org/10.1351/goldbook.A00028). 2) polarization (http://doi.org/10.1351/goldbook.P04712). Source: PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 324 (https://doi.org/10.1351/pac200779030293) Citation: 'dichroism' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. https://doi.org/10.1351/goldbook.DT07357 License: The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. Disclaimer: The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using.