L.R. (Address not stated) In: S.l.L. 20 Congress Copenhagen PubI.by: DIS Congress Service. 3 Knabrostraede. DK~I2l0. Copenhagen K. Denmark I977 306 p. en. Incident light-energy and light-distribution in algal cultures can be measured by using a planar silicon photodiode ... The apparatus described here. costing less than S40 (January I977). is designed to detect a voltage differential between ... The voltage will remain olf and the alarm \\ ill continue until a reset button is pressed.