How to Using Diodes as a photosensor Circuit diagram

A photo diode is a PN junction or PIN structure that when light reaches the junction, it excites an electron thereby creating a free electron positively charged. This mechanism is also known as the photoelectric effect, common in transistors, diodes and ICs are made ​​of semiconductors, and contain PN junctions. Almost all of the potentially active constituents are a photo diode and may be used as a photo sensor. The PN junction needs to be exposed to light, so to use a semiconductor diode as a light bulb must have a transparent glass, these diodes with  these characteristics can be used to measure the light intensity.

 Circuit diagram of a light intensity meter with diode.

 a test circuit diode light sensor

List of components:
D1 1n148 or any other photo-sensitive element
T1, T2 BC548 or similar
C1 680n
R1 2M

Above this circuit that is very popular, it works with LEDs, photodiodes and photo-resistors. V is a voltmeter which can be a multimeter.