A cooling unit (2) having a pump (20) for generating an airflow is provided for cooling a High Power lamp (10) during operation. The value of the airflow is controlled by a control unit (3) which comprises a driver (30) for determining a required value of the airflow on the basis of the operating power of the lamp (10). The control unit (3) comprises two pressure sensors (32, 33) for measuring a pressure of the airflow as well as a pressure drop of the airflow across an orifice (31). The driver (30) is designed for processing the measuring results in order to determine an actual value of the airflow. The value of the airflow is accurately controlled by adjustment of the power supply to the pump (20) in order to obtain a match of the actual value of the airflow and the required value of the airflow.