LDR: LDR is a photo resistor, It work to only light source and when light s increase and LDR resistivity increase .It lights low and resistivity low and LDR is a light dependent resistor. And it is one type resistor. Unit K amper LDR Material: Cadmium sulphide(cds) Lead Sulphide (Pbs) k USES : It is a active sensor . It use automated electronic devices. It use street light,and sun Ray detected solar panel and others.