A method for controlling a light intensity in an enclosed cultivation space for plants/crops, said enclosed cultivation space having a light regulating system including an artificial light source for emitting artificial light, the method comprising: at a first operating point, at which the light regulation system is operating at a light intensity setpoint: using the light source to at least temporarily cause an increase in intensity of artificial light, detecting an increase in fluorescence light emitted by the plants/crops as a result of the increase in intensity of artificial light, and calculating a first fluorescence gain as said increase in fluorescence light divided by said increase in intensity of artificial light; at a second operating point, at which a light intensity in the cultivation space is different from a light intensity in said first operating point: using the light source to at least temporarily cause an increase in intensity of artificial light, detecting an increase in fluorescence light emitted by the plants/crops as a result of the increase in intensity of artificial light, and calculating a second fluorescence gain as said increase in fluorescence light divided by said increase in intensity of artificial light; when the light intensity in the second operating point exceeds the light intensity in the first operating point, and the second fluorescence gain is greater than the first fluorescence gain, increasing the light intensity setpoint; and when the light intensity in the second operating point is less than the light intensity in the first operating point, and the second fluorescence gain is greater than the first fluorescence gain, decreasing the light intensity setpoint. at a first operating point, at which the light regulation system is operating at a light intensity setpoint: using the light source to at least temporarily cause an increase in intensity of artificial light, detecting an increase in fluorescence light emitted by the plants/crops as a result of the increase in intensity of artificial light, and calculating a first fluorescence gain as said increase in fluorescence light divided by said increase in intensity of artificial light; using the light source to at least temporarily cause an increase in intensity of artificial light, detecting an increase in fluorescence light emitted by the plants/crops as a result of the increase in intensity of artificial light, and calculating a first fluorescence gain as said increase in fluorescence light divided by said increase in intensity of artificial light; at a second operating point, at which a light intensity in the cultivation space is different from a light intensity in said first operating point: using the light source to at least temporarily cause an increase in intensity of artificial light, detecting an increase in fluorescence light emitted by the plants/crops as a result of the increase in intensity of artificial light, and calculating a second fluorescence gain as said increase in fluorescence light divided by said increase in intensity of artificial light; using the light source to at least temporarily cause an increase in intensity of artificial light, detecting an increase in fluorescence light emitted by the plants/crops as a result of the increase in intensity of artificial light, and calculating a second fluorescence gain as said increase in fluorescence light divided by said increase in intensity of artificial light; when the light intensity in the second operating point exceeds the light intensity in the first operating point, and the second fluorescence gain is greater than the first fluorescence gain, increasing the light intensity setpoint; and when the light intensity in the second operating point is less than the light intensity in the first operating point, and the second fluorescence gain is greater than the first fluorescence gain, decreasing the light intensity setpoint.