Optical properties of the marine diatom Thalassiosira pseudonana were examined in nitrate‐limited semicontinuous cultures for growth rates ( µ N ) varying from 0.22 to 1.32 d −1 . Two experiments were conducted at each growth rate in which sampling of the culture was done at either the dark‐to‐light (D‐L) or light‐to‐dark (L‐D) transition of a 12‐h photoperiod. Optical cross sections and efficiency factors for absorption, scat...