A Comprehensive Guide to Home Security Systems:

Photodiode:

 The photodiode is an electronics device which used  for sense light is called photo diode

OR 

A diode is is used in reverse -bias. Light allow to strike 

"junction" Ammeter/Switch is connected in series with a cell.This process is called photodiode.

You may also like

How photodiode Working:

photo execute an atom in depletion layer converts it to hole- electron pair. Before it recombine they are separated by electric field  across depletion layer.Can create current in the current.With proper reverse voltage current is saturated for the give light.

similarly if light is increased another saturated current is formed j2, The voltage in battery is set of saturation current.Then in the output we get relation current I*Light intensity.

Uses OF photodiode:

• It uses in automatic shutter control and light meters.
• It uses in cat scanners - x ray detection. pulse oximeters.
• It uses in safety equipment ,smoke detection,pulse oximeters.
• It uses in automatic and headlight dimmer.
• It uses communication ,Fiber optic links.
• It is uses in Industry, Bar code scanner

LED (light emitting diode):

A light emitting diode is a semiconductor device which define like Those device which can emit light when the electric current pass through it is called light emitting diode.

WORKING:

When current flow n forward bias the recombination of holes- electrons become faster due to high concentration and spring  electric field.Every recombination emits E/m waves of frequency =f=eg/h Every recombination emits E/m waves of frequency =eg/h.Since high eg is used the frequency is within range of visible light.The light  wave bright-up the resin capsule.

this is L.E.D.

Uses of LED (light emitting diode):

• It is used in traffic signal and burglar alarms system.
• It is used in aviation lighting.
• It is used in microprocessors and multiplexers.
• It is used in digital computer and calculator.
• It is used in camera flashes and automotive heat lamps.