Abstract: The invention relates to a radiation source including: an illuminant; a first optical element; and a sensor. The sensor is designed appropriately and is connected to the first optical element appropriately such that the sensor can be used to determine a change of a parameter of the first optical element over time, whereby the parameter affects an optical property of the radiation source. Moreover, the invention relates to a method for the producing a product involving the provision of a radiation source according to the invention as well as to a use of the radiation source to increase the efficiency of conversions or changes of state of educts to products.