The invention relates to a circuit arrangement for detecting a crest factor of a lamp current or a lamp operating voltage of an electric lamp (2), the circuit arrangement having a first subcircuit (15), which is designed to determine an averaged value from an input signal applied to the circuit arrangement, having a second subcircuit (16), which is designed to determine a maximum permissible value from the input signal applied to the circuit arrangement and having a comparator circuit (17), which is designed to produce a comparison signal from the output signal of the first subcircuit (15) characterizing the averaged value and from an output signal of the second subcircuit (16) characterizing the maximum permissible crest factor. The invention also relates to a method for detecting such a crest factor. One further aspect of the invention relates to an electronic ballast (1) which has a circuit arrangement (14a, 14b) according to the invention. Furthermore, the invention also relates to a method for operating an electric lamp, in which a crest factor is detected in accordance with a method according to the invention.