| Optical Density |
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Optical density is the Absorbance of an optical element for a given Wavelength λ per unit distance: : Where: Although absorbance doesn't have true units, it's 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 sometimes defined without regard to the length of the sample; in this case it is a synonym for absorbance. Neutral Density Filter s are typically quantified this way. REFERENCES |
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