optical density

Also found in: Dictionary, Thesaurus, Medical, Financial, Acronyms, Wikipedia.

optical density:

see refractionrefraction,
in physics, deflection of a wave on passing obliquely from one transparent medium into a second medium in which its speed is different, as the passage of a light ray from air into glass.
..... Click the link for more information.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Optical Density


a measure of the opacity of a layer of a substance to light rays. The optical density D is equal to the common logarithm of the ratio of the radiation flux F0 incident on the layer to the flux F that has been attenuated by absorption and scattering in passing through the layer: D = log (F0/F). In other words, the optical density is the logarithm of the reciprocal of the transmission coefficient of a layer of a substance: D = log (1/τ). In the definition of natural optical density, a concept that is also sometimes used, the common logarithm is replaced by the natural logarithm.

Figure 1. Types of optical density of a layer of a medium classed according to the incident radiation’s geometry and the method used to measure the transmitted radiation flux, (a) The specular optical density Dǀǀ is determined by directing a parallel flux perpendicular to the layer and measuring only the part of the transmitted flux that retains the original direction, (b) To determine the totally diffuse optical density D, a parallel flux is directed perpendicular to the layer and the entire transmitted flux is measured, (c) and (d) Methods of measuring two types of doubly diffuse optical density D; the incident flux is uniformly diffuse. The difference DǀǀD is a measure of the light scattered in the layer under examination. In the sensitometric system used in the USSR the terms “regular,” “integral,” and “diffuse” are found instead of “specular,” “totally diffuse,” and “doubly diffuse,” respectively.

The concept of optical density was introduced by R. Bunsen. It is used to characterize the attenuation of optical radiation, or light, in layers and films of such various substances as dyes, solutions, stained glass, and milk glass, as well as in light filters and other optical products. The concept of optical density is especially widely used in the quantitative evaluation of developed photographic emulsions in both black-and-white and color photography; the methods used to measure it constitute the subject of densitometry. There are several types of optical density, depending on the nature of the incident radiation and the method of measurement of the transmitted radiation flux (Figure 1).

Optical density depends on the set of frequencies ν or wavelengths λ characterizing the initial flux; its value for the limiting case of one unique v is called the monochromatic optical density for this frequency. The specular monochromatic optical density (Figure 1,a) of a layer of a nondispersive medium is, not taking into account corrections for reflection from the front and rear boundaries of the layer, equal to 0.4343 kv l, where kv is the natural absorption coefficient of the medium and l is the thickness of the layer. Actually, kv l = kcl, which is the exponent in the equation of the Bouguer-Lambert-Beer law. If the scattering in the medium cannot be disregarded, kv is replaced by the natural attenuation coefficient. For a mixture of nonreacting substances or a series of media placed one on top of another, this type of optical density is additive—that is, it is equal to the sum of the optical densities of the individual substances or media. The same is true for specular polychromatic optical density, where the radiation has a complex spectral composition, in the case of media with nonselective absorption, that is, absorption independent of v. The specular polychromatic optical density of a series of media with selective absorption is less than the sum of the optical densities of the media.


Gorokhovskti, Iu. N., and T. M. Levenberg. Obshchaia sensitometriia: Teoriia i praktika. Moscow, 1963.
James, T., and G. Higgins. Osnovy teorii fotograficheskogo protsessa. Moscow, 1954. (Translated from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

optical density

[′äp·tə·kəl ′den·səd·ē]
The degree of opacity of a translucent medium expressed by log I0/ I, where I0 is the intensity of the incident ray, and I is the intensity of the transmitted ray. Abbreviated OD.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
coli cell suspension, the three measured optical density spectra (230-820 nm) are collected (Figure 7); according to the proposed analysis, several parameters are calculated in Table 3, and their relative standard deviation (RSD) is less than 5%.
The final optical density strongly correlated with the methanol content, and the amount of methane increased proportionally.
Indented Protruding 0 + ++ 0 + ++ MMP-2 <1 month 0 1 0 1 0 2 1-12 months 0 2 2 4 1 0 >12 months 2 2 1 7 1 1 MMP-9 <1 month 1 0 0 1 1 1 1-12 months 1 1 2 4 1 0 > 12 months 3 1 1 5 1 3 Table 5: Mean optical density of elastogenesis and degradation markers in anetoderma.
Then, the mixture was gently stirred and after 30 minutes the optical density was measured.
In this work, the print quality was determined as the properties of the print (i.e., the optical density of the full-tone area), the color values ([L.sup.*], [a.sup.*], [b.sup.*]) and gloss, as well as the mechanical properties of print (i.e.
TABLE 1: MTT assay of cell viability and optical density of TH positive PC12 cells.
Range, volume, diameter and integrated optical density of lymph follicles were significantly higher in TH.
The UVSCALE, in which color optical density changes according to the accumulated amount of UV light, enables to visually examine if the entire surface of the subject is equally irradiated with UV light.
Those systems have features of capability of observing many samples simultaneously and non-destructively with a overwhelmingly little work, capturing the obtained data dynamically and obtaining them in the quantitative, in comparison with agar colony counting method and optical density measurement method with which a microbial activity is observed in the stationary condition.
Though IgM and IgG are detectable by the 7th day of PDI, the dominant antibody is IgM as demonstrated by IgM/IgG optical density ratio of more than the assay cut-off value (studies have used a cut-off value of >1.2 with patient sera in 1/100 dilution or >1.4 with patient sera in 1/20 dilution).
The wide dynamic range improves purity estimates by allowing for impurity detection at low optical density. Finally, results can be analyzed using Image Lab 5.0 software.

Full browser ?