Reply to "commentary on photosynthesis and negative entropy production by Jennings and coworkers" by J. Lavergne.

It is argued that the chemical potential analogy does not provide useful information on the thermodynamics of photosystems, as the thermodynamic efficiency of an absorbed quantum is not considered. Instead, the approach based on either entropy balance or entropy flux considerations does provide this information. At high thermodynamic efficiencies, primary photochemistry can, in principle, violate the Second Law of Thermodynamics.