Definition of: actinometer

(ak′ti·nom′ə·tər) noun
1. An instrument for measuring the heat intensity of the sun's rays and for determining the actinic effect of light rays.
2. An instrument for determining the power of radiation by its chemical effect on gases, acids, etc.
—ac·ti·no·met·ric (ak′ti·nö·met′rik) or ·ri·cal adjective
—ac′ti·nom′e·try noun