Light dependent resistors are two cadmium sulphide (cDS) photoconductive cells with responses similar to that of the human eye. The cell resistance falls with increasing light intensity. 

Solid-state photosensor that uses photoconductivity to lower resistance value when irradiated with light 
Ceramic package with sensitivity up to 690 nm 
TO-5 and TO-18 packages 
Suitable for use in applications like street light auto-flashers and camera light metres

Applications

Applications include 
Smoke detection 
Automatic lighting 
Control batch counting 
Burglar alarm systems