- a device containing a set of vanes that are blackened on one side and suspended on an axis in a vacuum: the vanes rotate on exposure to sunlight
- an instrument for measuring radiant energy in any part of the electromagnetic spectrum
Origin of radiometerradio- + -meter
- A device that measures the intensity of radiant energy, consisting of a partially evacuated glass bulb containing lightweight vertical vanes, each blackened on one side, suspended radially about a central vertical axis to permit their revolution about the axis as a result of incident radiation. Also called light mill .
- An instrument that detects electromagnetic radiation.