The BPW34 with Silicon Photocell Plugin RoHS is a light sensitive diode manufactured by Siemens. It is a high-quality, low-cost alternative to traditional photoresistors with superior spectral response, low noise, low thermal resistance, and low capacitance. The diode measures the amount of light emitted from a source and converts it into an electronic signal that can be read and used by a variety of devices. It is RoHS (Restriction of Hazardous Substances) compliant and features no hazardous materials in the construction of the device. It has a wide range of uses from sensing ambient light in darkness activated applications to measuring the intensity of medical lighting.