Expression		Term (synonyms}

 T = I1/I0		Transmission, T (transmissivity, transmittance)

 %T = 100 x T		Percentage Transmission

 A= 1-T			Absorption

 E = log10 ( I0/I1 )	 Extinction (E) (optical density, absorbance)

 E = 1/cd(E)		Molar Extinction Coefficient, E, epsilon
			c in moles per liter, d in centimeters.

 E = k1d(cm)		k, extinction coefficient (Lambert's Law)

 E = k2c (g./1.)	c, concentration (Beer's Law)


 E = kcd		Simplified expression, Lambert-Beer Laws.
 
  , lambda		Wavelength

 A (Å) (AU)		Angstrom = l0-10 m., -or-
                        = 1/6438.5 x wavelength of Cd line
                        Angstrom Unit

  , micron, 10-6m 	=  l,000 millimicrons (or nanometers, nm) 
			= l0,000 Angstroms, A

       dlE2
 c2 = ------ . c1	regression line
       d2E1

Note: That there are three potentially confusing usages of the symbol 'A' in the literature on light. One, Absorption, appears on some spectrophotometer meters as the complement of T, Transmission of light, (i.e. A = 1 - T). This Absorption should not be confused with Absorbance, which is a synonym of Optical Dentisty or Extinction and is defined as E = log₁₀ ( I₀/I₁ ).
Additionally the measure of distance and resolution of light related methods is often given in Angstroms which is properly abbreviated with the symbol Å, but through carelessness is simetimes given the erroneous symbol 'A'.

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From class notes of the late Arthur W. Pollister
Page maintained by JG Kunkel