actinometer

/ˌæktɪˈnɑmɪtər/
noun
  1. An instrument that measures the intensity of radiation, especially sunlight.
    • Gardeners sometimes use an actinometer to decide where to place plants that need full sun.
    • The weather station's actinometer showed a sharp drop in radiation as the clouds rolled in.
    • The scientist used an actinometer to record the amount of solar energy reaching the ground.
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