Irradiance was investigated at Nsugbe with a cadmium sulphide (CdS) photoresistor. It is observed that cadmium sulphide photoresistor with an efficiency of 7% corresponds to maximum average hourly irradiance of 65 W m−2if the CdS were 100% efficient. Comparison of results with the modified empirical equation of Rapp and Hodman showed reasonable agreement between recorded and theoretical results of hourly irradiance in W m−2.