Difference between LDR and Photodiode

LDR vs Photodiode

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.

In applications, the LDR can function well when used in street lighting circuits, as it will measure the varying light intensities and switch the lights on when a certain threshold is met. On the other hand, photodiodes are preferred to be used in precision equipment such as laboratory equipment, which is very specific. Use of the photodiode will therefore be seen in instruments like the spectrometer, analyzers and other digital precision circuits.

Summary

LDR and photo diode are two very commonly used photo sensors
LDR refers to the Light Dependent Resistor (LDR)
LDR is the most commonly used photo sensor
Photodiode is used in applications that can only do with two values: either on or off
LDR varies the light depending on certain factors
Photodiode has a quicker response time as opposed to LDR which is analog
LDR is a bidirectional resistor whereas photo diode is a unidirectional resistor
Both LDR and photo resistor have low costs
LDR is best suited for rugged environments
Examples of LDR in use is street lights
Examples of photodiodes in use is precision equipment like laboratory appliances e.g. spectrometer.

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