The construction of a versatile, single‐beam spectrophotometer expanded from a previously reported circular dichrometer utilizing an elasto‐optic modulator (EOM) for producing circular polarization, is described. The new spectrophotometer is capable of measuring circular dichroism as well as linear dichroism and light‐induced changes in absorbance and fluorescence yield, the latter being two of the most commonly measured properties in photosynthesis research. The use of an EOM, along with a phase‐sensitive detector, affords high sensitivity and at the same time, in conjuction with a mechanical phosphoroscopic device, a high degree of immunity from artifacts in studies employing actinic light. A description is given of the generation and use of timing signals essential for control and signal processing. Its performance is illustrated by examples drawn from light‐induced absorbance and fluorescence‐yield changes associated with photosynthetic electron transport and changes in redox state of electron carriers. This photometer, with very little modification, may also be used to perform a host of other types of measurements.