This is a very small light sensor. A photocell changes (also called aphotodetector, photo resistor, CdS or photoconductive cell) resistance depending on the amount of light it is exposed to. These little sensors make great ambient light triggers (when light in the room turns on, do something).Features:Light resistance : ~1k OhmDark resistance : ~10k OhmMax voltage : 150VMax power: 100mWDimensions:2 x 4 x 5mm4mm between pins31mm lead lengthDocuments:Datasheet