actinometer actinometer /ˌækˈtɪnəˌmɪtər/

noun

1. () An instrument for measuring the intensity of electromagnetic radiation (usually by the photochemical effect)  ( actinometer )
   an instrument for measuring the intensity of electromagnetic radiation (usually by the photochemical effect)
    The scientist used an actinometer to measure the intensity of the sun's rays.
   The scientist used an actinometer to measure the intensity of the sun's rays.