Technology 4 – Multimedia
Light Dependant Resistor ( Light Sensors)
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How The Device Operates
Light sensors are components of circuits that are able to measure light
and increase or decrease their resistance accordingly. Resistance refers to
the amount of electrical current or voltage that is held back by a certain
part of the circuit, in this case because of a component called a Resistor.
Compared to most resistors which have a set resistance and therefore
resist a specified amount of electrical current through a circuit, this one is
a bit more advanced with its resistance able to be altered under varying
brightness’s of light, hence being referred to as a variable resistor. This
varying resistance allows for eg. A dimming LED based on how bright or
dark a room is.
Using a strip of photo resistive material ( Cadmium Sulphide), this strip
measures the amount of light energy entering and adjusts its resistance,
lower for bright light such as a torch shining on it, or a much higher
resistance such as in a dark room. As a result if this was to be placed in a
circuit with a light bulb or LED attached, during darkness the, light
bulb/LED would be extremely dim or even out. During times of bright
sunlight, or a torches beam of light, the Light bulb/LED will shine bright
due to the lack of resistance in the circuit.
Images from - http://www.electronics-tutorials.ws/io/io_4.html
Daniel Debono S3236966 - Green
Technology 4 – Multimedia
What The Device is Typically Used For?
Being a resistor this device is usually used in as part of a circuit where the
light levels around this circuit will affect another component on the circuit
board eg. An LED, a buzzer etc. As it uses ambient light as its variable it
is especially useful in situations where artificial light needs to be created
only at certain times of day the day such as for solar powered garden
lights. On a larger scale, these light sensors are used in street lights you
find where you drive and also in digital cameras as one of many functions
that enables the auto flash function to work. As well as this, on production
lines where large numbers of products need to be counted lights sensors
can be used as they pick up the differing light from the product to be
counted and the conveyor belt it is on.
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How Can it Be Interfaced With The Arduino Micro-controller?
Using an external breadboard that is wired to the Arduino you can place
various components on that can form an electrical circuit that can be
controlled further by a set of codes that you write for the Arduino.

Here are some snapshots from a video that I found on the internet of an
Arduino board with a breadboard mounted on top with a resistor, light
dependant resistor and LED connected. Contrast to
what was mentioned before about “no light = high
resistance, light= low resistance” the creator of the
video input a code to reverse this to make it more
useful.
Hand away from sensor, light hits sensor, LED off
Hand over sensor, no light hitting sensor, LED on
Example from - http://au.video.yahoo.com/watch/3387081/9473589
Daniel Debono S3236966 - Green
Technology 4 – Multimedia
Using the program Processing, we are able to send lines of code to the
Arduino board like shown above to change the output of the circuit. An
example of this is shown in the circuit below.
The board is equipped with wires to connect it to the Arduino as well as a
resistor and Light Sensor. By inputting some simple code into the
Processing Program you can use the Light Sensor a data collector which
sends its information into the computer. These two images below are
actually from the render screen in Processing. The one on the left shows a
light sensor in darkness, the one on the right shows on in light. As you
can see data that the light sensor received is being relayed back to the
computer and rendered through the code as a visual display of how much
light is available in the area of the sensor.
Example and full Tutorial from -http://webzone.k3.mah.se/projects/arduinoworkshop/projects/arduino_meets_processing/instructions/ldr.html
Daniel Debono S3236966 - Green
Technology 4 – Multimedia

Examples of Interactive Projects Using This Sensor Technology
A personal project that I am thinking of using this light sensor on is for
lighting up a certain area under a veranda where my mum cooks dinner
sometimes. I have been hoping to place a combination of low wattage
lighting powered by some solar panels to light up the place. By using the
light sensor technology, these lights can auto turn on and off to save
electricity and provide light for when it is needed.
This same idea could be set up for some kind of miniature night light that
could be set up in a small enclosure in my room so I don’t trip over in the
darkness on my way to turn on the light to prevent that very thing
happening . Instead of the AC mains powered night lights, a simple USB
powered Arduino could provide the energy needed for an array of LEDs
which could create a custom night light for use in my room.
This idea could also be used for an alarm clock to wake you up when the
sunrises. This idea would require a simple circuit attached to a speaker or
some sort of mp3 player and when the sun rises the programming would
play a sound through the speaker to wake you up.
Bibliography
http://www.libelium.com/squidbee/index.php?title=Adding_a_light_sensor
http://www.token.com.tw/resistor/photo-cds.htm
http://en.wikipedia.org/wiki/Light_Dependent_Resistor
http://www.electronics-tutorials.ws/io/io_4.html
Daniel Debono S3236966 - Green