A system for measuring light absorption levels includes a light source providing a light beam and a container for a liquid. The container includes an opening to provide access to the liquid. A prism is disposed over the opening and is operable to direct at least a first portion of the light beam toward the opening to the liquid such that the at least a portion of the first portion of the light beam is reflected back from the liquid forming an attenuated beam. A detector is operable to measure at least one of a portion of the attenuated beam and a second portion of the light beam. The detector is operable to produce at least one of a liquid measurement signal and a reference signal. A device is operable to compute a ratio of the liquid measurement signal to the reference signal to determine a signal ratio.