Abstract: Method for the control of a burner equipped with an injector nozzle, said method comprising the steps of continuously during combustion optically monitoring the flame of the burner; subjecting the light from the burner to spectral analysis for determining the instantaneous value of the air factor in the combustion gases, and controlling the supply of fuel and/or combustion air to the burner in dependence of said instantaneous value of the air factor. The method is characterized in that light emitted from the central portion of the flame which penetrates through the nozzle opening through which fuel is injected into the combustion chamber is picked up in a point situated in the immediate vicinity of, behind and axially with said nozzle opening, said light being further conducted out of the nozzle for being subjected to spectral analysis.