We report an experimental realization of Maxwell’s demon in a photonic setup. We show that a
measurement at the few-photons level followed by a feed-forward operation allows the extraction of work
from intense thermal light into an electric circuit. The interpretation of the experiment stimulates the
derivation of an equality relating work extraction to information acquired by measurement. We derive a
bound using this relation and show that it is in agreement with the experimental results. Our work puts
forward photonic systems as a platform for experiments related to information in thermodynamics.