Accurate Measurement of Active Power of Discharge Lamps

The active power provided to a discharge lamp appears strictly related to its luminous flux, therefore an accurate measurement of the power is required to grant stable lamp operation. A technique is presented to reach a measurement on the power with a relative uncertainty of about 0.01%. The method is based on two commercial digital multimeters with integrating analog to digital converter. The main causes of uncertainty are considered and their contributions are evaluated. The case of a 150 W sodium lamp is considered as an example