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Additional recommended knowledge
Although absorbance does not have true units, it is quite often reported in "Absorbance Units" or AU. Accordingly, optical density is measured in ODU, which are equivalent to AU cm−1.
The higher the optical density, the lower the transmittance. Optical density times 10 is equal to a transmission loss rate expressed in decibels per cm, e.g., an optical density of 0.3 corresponds to a transmission loss of 3 dB per cm.
Optical density is often defined without regard to the length of the sample; in this case it is a synonym for absorbance. Neutral density filters are typically quantified this way. Some filters, notably welding glass, are rated by shade number, which is 7/3 times the optical density. A shade number of 14 is regarded as safe for direct observation of the sun.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Optical_density". A list of authors is available in Wikipedia.|