Fluctuation frequency (F) of an ambient light (S) is identified by: A) specifying first frequency (F1) and second frequency (F2), higher than said first frequency; B) measuring an optical power of the ambient light with a signal receiver (2) over a measuring time interval (Ti) during a total measuring time (T), which is shorter than or equal to a first cycle duration (P1) belonging to the first frequency; C) detecting the optical power of the ambient light in a time series over the total measuring time; D) determining at least one detection feature for identifying the fluctuation frequency by evaluating the time series; and E) identifying the fluctuation frequency of the ambient light as the first frequency or as the second frequency using the at least one detection feature.