Abstract10,10′‐Dimethyl‐9,9′‐biacrilydene in pinacolone reacts with ozone at −45°C to give a thermally unstable product, the decomposition of which results in N‐methylacridone and emission of light with a quantum yield of over 10−2Einstein · mole−1, showing the reaction to be one of the most efficient chemiluminescent reactions known. As the chemical reaction is known to yield dioxetanes and the primary exited product is shown to be N‐methylacridone, positive evidence is provided that the Lucigenin light reaction proceeds via a d