A method of influencing or of controlling a mixing ratio of combustion air and a gaseous fuel comprising more than twenty percent of hydrogen gas, wherein the combustion air and the gaseous fuel are combusted together in a combustion chamber, the method comprising the steps of: at least one first optical sensor recording a first raw signal directly originating from a flame inside the combustion chamber, producing a first sensor signal from the first raw signal, and sending the first sensor signal to a controller; at least one second sensor (4, 5) within a flame zone of the combustion chamber recording a third electric signal, producing a third sensor signal from the third electric signal, and sending the third sensor signal to the controller; the controller determining a first signal strength of the first sensor signal; the controller determining a third signal strength of the third sensor signal; after recording the first raw signal, changing a supply of the combustion air and/or of the gaseous fuel to the combustion chamber; after the change in supply, the at least one first optical sensor recording a second raw signal directly originating from the flame inside the combustion chamber, producing a second sensor signal from the second raw signal, and sending the second sensor signal to the controller; the controller determining a second signal strength of the second sensor signal; after the change in supply, the at least one second sensor (4, 5) within the flame zone of the combustion chamber recording a fourth electric signal, producing a fourth sensor signal from the fourth electric signal, and sending the fourth sensor signal to the controller; the controller determining a fourth signal strength of the fourth sensor signal; the controller determining a change in signal strength as a function of the first signal strength and as a function of the second signal strength and as a function of a further signal strength selected from the third and the fourth signal strengths, the change in signal strength being caused by the change in supply of the combustion air and/or of the gaseous fuel; and the controller controlling or setting the supply of the combustion air and/or of the gaseous fuel as a function of the change in signal strength. at least one first optical sensor recording a first raw signal directly originating from a flame inside the combustion chamber, producing a first sensor signal from the first raw signal, and sending the first sensor signal to a controller; at least one second sensor (4, 5) within a flame zone of the combustion chamber recording a third electric signal, producing a third sensor signal from the third electric signal, and sending the third sensor signal to the controller; the controller determining a first signal strength of the first sensor signal; the controller determining a third signal strength of the third sensor signal; after recording the first raw signal, changing a supply of the combustion air and/or of the gaseous fuel to the combustion chamber; after the change in supply, the at least one first optical sensor recording a second raw signal directly originating from the flame inside the combustion chamber, producing a second sensor signal from the second raw signal, and sending the second sensor signal to the controller; the controller determining a second signal strength of the second sensor signal; after the change in supply, the at least one second sensor (4, 5) within the flame zone of the combustion chamber recording a fourth electric signal, producing a fourth sensor signal from the fourth electric signal, and sending the fourth sensor signal to the controller; the controller determining a fourth signal strength of the fourth sensor signal; the controller determining a change in signal strength as a function of the first signal strength and as a function of the second signal strength and as a function of a further signal strength selected from the third and the fourth signal strengths, the change in signal strength being caused by the change in supply of the combustion air and/or of the gaseous fuel; and the controller controlling or setting the supply of the combustion air and/or of the gaseous fuel as a function of the change in signal strength.