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Percentage of transmission and optical density

The percentage of transmission (% T) is the unit most commonly used to express quantitatively as an optical filter transmits light. The percentage of transmission is measured at a particular wavelength (or range of wavelengths) and is the ratio between the intensity of transmitted light (I) for the intensity of incident light (I), expressed as a percentage :

Të% = I / I * 100

The following diagram illustrates the terminology typically used when talking about ghosts, expressed in% T.

The level of attenuation (or block level) and the range of attenuation (or range of blocking) filters are usually defined in units of optical density (OD). The optical density use the same units of the amount of absorption and is expressed as negative log of the transmission. Note that you should not try to deduce the optical density by a pattern of transmission, a common mistake made ??by those working with fluorescence.
Expressed mathematically:

OD=-log Të=-log [(% Të) / 100

Example: OD 4.5 = 3 x 10 -5 T (0.003 %T)

Attenuation Nomenclature