BIO RAD SmartSpec 3000 Instruction Manual page 9

The Lambert-Beer's law identifies the relation between sample concentration and the
intensity of transmitted light. Absorbances and % transmittances are defined by the following
equations:
% Transmittance (%T)
-εcl
%T = I /I * 100 = 10
t 0
Absorbance or optical density (A or O.D.)
A = log 1/T = log I
10 10
Where I = Intensity of incident light
0
I = Intensity of transmitted light
t
ε
= Molar extinction coefficient (liter/mole/cm)
c = Sample concentration (mol/liter)
l = Optical pathlength
Sample concentration C
Incident light l
o
l l l l
Fig. 6. Lambert-Beer's law.
A = log 1/T
Transmittance
100
Fig. 7. Relationship between Transmittance and Concentration and Absorbance and
Concentration.
* 100
εcl = εcl
/I = log 10
0 t 10
-ε ε cl l l l
Transmitted light l = l 10
t o
Concentration
6
A = εcl
Absorbance
Concentration