The transmittance is the ratio of the transmitted radiant power to the incident radiant power.1
The diagram above shows how a single-beam visible spectrophotometer detects absorption of a sample. A continuum light source outputs white light, which then passes through a wavelength selector. A small band of light then passes through the sample of some length. The sample absorbs some of the light and passes the rest through, which is then measured by the light detector.
Description
The equation is:
where
- P0 is initial irradiance from the wavelength selector to the sample in units of (Energy/ sec * area of light beam)
- P is irradiance from the sample to the light detector in units of (Energy/ sec * area of light beam)
- T is transmittance2
Related Topics
- Absorbance (for the Spanish site click here)
- Beer's Law (for the Spanish site click here)
References
1. IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook.Last update: 2014-02-24; version: 2.3.3.DOI of this term: doi:10.1351/goldbook.T06484.
2. Harris, D., Quantitative Chemical Analysis, 9th Ed., W. H. Freeman, Pp.435(2015).