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Light intensity based lamp dimming
BLOCK DIAGRAM
DC Power Supply
Light Sensor
LDR INPUT
MICROCONTROLLER
ATMEGA8
TRIAC
BASED
Dimmer
AC Lamp
AC Supply
INTRODUCTION
This project consist of intensity control of light as per requirement. the intensity of light
is measure by sensor LDR i.e Light Dependent Resistor . sensor give output to
microcontroller and gives signal to dimmer as per program dimmer work depends on
signals comes from microcontroller and the intensity of lamp light is controll by
dimmer connected to lamp
WORKING
A photoresistor or light dependent resistor (LDR) is a resistor whose resistance
decreases with increasing incident light intensity. It can also be referred to as a
photoconductor.
A photoresistor is made of a high resistance semiconductor. If light falling on the device
is of high enough frequency, photons absorbed by the semiconductor give bound
electrons enough energy to jump into the conduction band. The resulting free electron
(and its hole partner) conduct electricity, thereby lowering resistance.
Thyristor (and briefly, thyratron) dimmers were introduced to solve some of these
problems. Because they use switching techniques instead of potential division, there is
almost no wasted power, dimming can be almost instantaneous and is easily controlled
by remote electronics. TRIACs are used instead of SCR thyristors in lower-cost designs
but do not have the surge-handling capacity of back-to-back SCRs and are only suitable
for loads less than about 20 amps
Dimmers are devices used to vary the brightness of a light. By decreasing or increasing
the RMS voltage and, hence, the mean power to the lamp, it is possible to vary the
intensity of the light output. Although variable-voltage devices are used for various
purposes, the term dimmer is generally reserved for those intended to control resistive
incandescent, halogen and more recently compact fluorescent (CFL) lighting. More
specialized pulse-width modulation equipment is needed to dim fluorescent, mercury
vapor, solid state and other arc lighting.
In the professional lighting industry, changes in intensity are called “fades” and can be
“fade up” or “fade down”. Dimmers with direct manual control had a limit on the speed
they could be varied at but this issue has been largely eliminated with modern digital
units (although very fast changes in brightness may still be avoided for other reasons
like lamp life)
Modern dimmers are built from silicon-controlled rectifiers (SCR) instead of
potentiometers or variable resistors because they have higher efficiency. A variable
resistor would dissipate power by heat (efficiency as low as 0.5). By switching on and
off, theoretically a silicon-controlled rectifier dimmer does not heat up (efficiency close
to 1.0)
Applications
Photoresistors come in many different types. Inexpensive cadmium sulfide cells can be
found in many consumer items such as camera light meters, street lights, clock radios,
alarm devices, and outdoor clocks.
They are also used in some dynamic compressors together with a small incandescent
lamp or light emitting diode to control gain reduction.
Lead sulfide (PbS) and indium antimonide LDRs (light dependent resistor) are used for
the mid infrared spectral region. photoconductors are among the best far-infrared
detectors available, and are used for infrared astronomy and infrared spectroscopy.
In a smoke detector, a light sensor can be used to measure the amount of light
transmitted by a known light source, such as an LED, through the air inside the sensor
assembly.
There are many other applications for light sensors, such as flame detectors, security
systems, lighting control, robotics, etc. In these applications, many of us think that since
the sensor produces an analog output, interfacing this type of sensor to a
microcontroller will require a conventional analog-to-digital converter.