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Abstract

A light level sensor for use in controlling the switching of artificial lighting. The sensor comprises a photoelectric transducer which provides an output signal at a level which is significant of the illumination level of incident light. An A-D converter and a microprocessor are located in circuit with the transducer for detecting the level of the transducer output signal and for any cyclic variation of the transducer output signal resulting from cyclic variation of the level of incident light. Further circuit means are provided for generating a sensor output signal if either (a) the level of the transducer output signal is below a predetermined level or (b) the level of the output signal is above the predetermined level and, at the same time, cyclic variations occur in the level of the transducer output signal. When the sensor is used to switch artificial lighting on, with falling ambient light, the sensor output signal is used to energise a lighting control relay when the ambient light falls below the predetermined level. The relay thereafter is held ON if the sensor detects the presence of a high light level, provided that the high light level is attributable only to the artificial lighting as recognised by detection of cyclic variation of the transducer output signal.

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First Claim