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 include
Smoke detection
Automatic lighting
Control batch counting
Burglar alarm systems

Photodiodes, Silonex