In the development process of intelligent household and workshop project, light intensity need to be detected in many cases. Considering the factors of cost and volume, both illuminometers and the light sensor modules sold on the market can hardly be applied to many occasions. In this paper two cheap photosensitive resistances are used for collecting light source at the same point, and the output after amplification of AD623 is acquired by MCU. By comparing measured values with the actual, the system has a good linearity and accuracy, and can achieve low cost and little volume. Moreover, the complexity of the circuit structure is reduced greatly through adopting a reasonable circuit design.