What are Absorbance Units?

ANSWER:

When referring to Absorbance measurements the units are usually indicated by AU for absorbance units (eg. Absorbance = 6 AU).

Absorbance        = log(1/Transmittance_λ)
                              = -log(Transmittance_λ)
Example:

Transmittance  = 10^-6
Absorbance      = –log (10^-6)
^-Absorbance        = log (10^-6)
10^-Absorbance   = 10^-6
Absorbance     = 6 AU