There's a bit of a language issue here.
The absorptivity A measured by a spectrometer is given by Beer's Law (or Beer-Lambert Law)
[tex]A = - log \frac {I}{I_0} = - log T = \epsilon c l[/tex]
(Logs are base 10). Let's work backwards. What does an absorptivity of 1 mean,for amount of light transmitted?
[tex] 1 = - log T[/tex]
Solving for T, T = 10-1 = 0.1, or 10% transmittance when A = 1.
A sample absorbing 10% would have a transmittance of 90%, or T = 0.9. In this case, A ~ 0.046.
So, a sample absorbing 10% won't have a value of A = 1, but rather a sample transmitting 10% will have a value of A = 1. This is one reason why it's a good rule of thumb to keep absorbance values below A = 1, because at higher values of A, the amount of transmittence becomes very low, which can lead to sensitivity issues.