# Measure Light Intensity using Photodiode

The Photodiode used is the BPW34. This is a high speed and high sensitive silicon PIN photodiode in a miniature flat plastic package. A photodiode is designed to be responsive to optical input. Due to its waterclear epoxy the device is sensitive to visible and infrared radiation. The large active area combined with a flat case gives a high sensitivity at a wide viewing angle.

Photodiodes can be used in either zero bias or reverse bias. Diodes have extremely high resistance when reverse biased. This resistance is reduced when light of an appropriate frequency shines on the junction. Hence, a reverse biased diode can be used as a light detector by monitoring the current running through it. Coupled to a 10Kohm resistor, and given the specification of the BPW34 a simple relationship between lux (light intensity) and voltage is given by

$$Lux = {1333 \times V_{o}}$$

The Light Application Adaptor for the EMANT300 has the photodiode BPW34 connected to AIN0 (input analog) of the DAQ module and the resistor connected to AINCOM.

The LabVIEW VI that reads the voltage across the resistor and converts the voltage to lux is called EMANT300 Example Photodiode.VI