The use of photosensors is increasingly being used in the world today
in many innovations, using the basic principle of using light for
sensing. A good example of photo sensors in use is the line-following
robot, which will makes use of this unique invention. Any project that
needs to employ the use of photo sensors must decide on the specific
type of invention to use. There are two commonly used types of photo
sensors and these are the Light Dependent Resistor (commonly abbreviated
LDR) and the photodiode. What specific differences do these two
photosensors have and what dictates regarding the type of sensor to use?
The specific properties of each sensor are the main dictator of where
and when they can be used.
The Light Dependent Resistor (LDR) is one of the most widely used and
preferred photo resistor in most projects that requires the use of a
photosensor. The most ideal characteristic it carries is that it is
cheap and rugged. This means it can be used in multiple projects. Also,
as the name of LDR denotes, their resistance to electricity depends on
the intensity of light shining on them. It can thus be said that their
resistance is inversely proportional to the amount of light they
receive. LDR are therefore the most preferred photosensors, whereby a
varying amount of light intensity is expected, as opposed to a light
intensity that is fixed.
The LDR is also preferred as the sensor of choice when a hardy build
is required. This is especially the case when the sensor is expected to
operate in a hardy and rough environment. The response time of LDR is moderate and it is also advantageous, as it is a bidirectional resistor.
The photodiode in itself comes with a quick response time and if
the build incorporates fast responses, them the photodiode is the
appropriate choice to make use of. The cost of the photodiode is also
low, just as that of the LDR. Contrary to use of LDR in varying
intensities of light, the photodiode is mainly used in the reverse bias,
turning off when a certain light intensity is exceeded. This means that
the photodiode has specifically two levels of output. Either it is off
when the light intensity is exceeded or on when the light intensity is
adequate. The use of the photodiode is therefore preferred in
environments where there is need to keep check of the light intensities.
From the action of the photodiode, it can be said to be unidirectional
in nature.
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