Light sensor

Light sensor convert light energy into electrical energy. The applications of light sensors range from their use in brightness control in your mobile phone to the agriculture to their use in security alarm system.

Types of light sensors

1. Photodiode
2. Photo resistor
3. Phototransistor

1. Photodiode

• Photodiode have found their application from the remote controls of televisions to smoke detectors.Photodiode consist of a PN junction which is connected in reverse bias where the P junction is connected to the negative terminal of the battery and the N terminal is connected to the positive terminal of the battery due to this a wide depletion layer is formed when photons from light fall on the depletion region it leads to the generation of electron and holes. The holes move toward the p junction and the electrons move towards the end junction this leads to the generation of charges which contribute to the flow of current thus the amount of current produced is directly proportional to the intensity of light

2. Photo resistor

• A photo resistor is a variable resistor whose resistance varies depending upon the amount of light that it is exposed. It can be used to detect the presence or absence of light. As light is exposed to the photo resistor the resistance decreases which leads to more current flow. They are used in clock sensors, automatic strength light, etc

3. Phototransistor

• Like the photodiode, phototransistors also conduct depending on the light falling on them. They are used for position, security system etc.
• The only difference here is that a transistor is being used. In photodiode, the light falling on the depletion region leads to the flow of charges. The photo transistor is more sensitive to light when compared to the photodiode.
• A camera captures what we see and produces it in digital form. CCD has light sensitive arrangement called pixels. A CCD is made up of millions of pixels. These pixels are p-layer of silicon separated by a depletion layer from an n-type silicon layer.