An instrument head is provided for attachment to a plurality of instrument handles having different power profiles. The instrument head contains an illumination assembly including at least one LED as well as a drive circuit for detecting a power profile of an attached instrument handle and converting variable voltages received from the attached instrument handle to a constant current for powering the at least one LED based on the power profile. Accordingly, the instrument head enables use with a plurality of instrument handles, including those originally configured for use only with incandescent light sources.