An Isotropic Light Sensor for Measurements of Visible Actinic Flux in Clouds

A low-cost isotropic light sensor is described consisting of a spherical diffuser connected to a single photodiode by a light conductor. The directional response to light is isotropic to a high degree. The small, lightweight, and rugged construction makes this instrument suitable not only for application on aircraft or under balloons but also on the ground in microclimatological studies. A vertical profile of actinic flux in the visible range (400‐750 nm) in Arctic stratus, obtained with this instrument under a tethered balloon during the FIRE experiment in 1998, is presented.