Hi L Jo
the Lag phase is non-exponential growth, the time time before exponential growth where bacteria are synthesizing enzymes, proteins and getting ready to divide.
It seems its 0-60 min.
The Log Phase or Exponential Phase exhibit exponential growth (doubling) or log increase in number.
The is after 60 minutes to 120-140 minutes, and Log phase or exponential transitions then to the stationary phase.
This phase is 140-180 minutes.
The amount of light transmitted through a sample is inversely proportional to cell number. So as transmitance is reduced as graphed above (black line) the bacteria increase as per discussion above.
To learn more about the relationship of Transmitance and Absorbance to cell number and counts see http://inst.bact.wisc.edu/inst/index...cle&art_id=112