Photoresistor sensor is generally used for light measurement, light control and photoelectric conversion conversion of light changes to electrical changes.
Principle: It works based on semiconductor photoelectric effect. The photoresistor has no polarity and is purely a resistor element. When used, DC voltage or AC voltage can be added. The working principle of photoresistor: when illuminated, the electric resistance is very small; when it is not illuminated, the resistance is very large. The stronger the illumination, the smaller the electric resistance; when the illumination stops, the electric resistance restores to its original value.
The resistance of a photoresistor which is not illuminated is called dark resistance, and the current flowing through it is called dark current.
The resistance which is illuminated is called bright resistance, and the current is called bright current. The bigger the dark resistance, the better it is; the smaller the bright resistence, the better it is. In practical application, the dark resistance is about mega-ohm while the bright resistance is about several thousand ohms. Home Products Products. Working Principle of the Light Sensor As we all know, nowadays, sensors have been widely used in human production and life.
Light Sensor Optical sensor is a sensor that converts light signal into electric signal by using photosensitive elements. Working Principle of Light Sensor Light sensor is also called photoresistor.
Photosensitive resistor Principle: It works based on semiconductor photoelectric effect. Spectral range: from ultraviolet area to infrared area. Light sensors are almost always a flat, one-sided surface, so the solid angle occupied by the sensor as viewed from the light source can change depending on its orientation.
With the light sensor perpendicular to the direction of the light, it is occupying the largest solid angle possible. As the light sensor rotates away from the light, its solid angle decreases, with the illuminance therefore also decreasing, until the light sensor ultimately detects no direct illuminance when parallel to the light beams or when facing away. This fact can be used to determine the angle of incidence of a light beam on the sensor.
Figure 2: Graph shows Illuminance vs Angle. Light sensors have a lot of uses. The most common use in our daily lives is in cell phones and tablets. Most portable personal electronics now have ambient light sensors used to adjust brightness.
If the device can sense that it is in a dark place, it turns down the screen brightness to save power and not surprise the user with a very bright screen. Another commonplace use for light sensors is controlling automatic lights in automobiles and streetlamps. Using a light sensor to trigger a bulb when it is dark outside saves the slight hassle of turning on the lights and saves power in the day when the sun is bright enough.
There are many more uses than consumer convenience, however. Detecting intrusion into containers or rooms is an important security application. When shipping expensive cargo, it can be important to know when a shipping container has been opened, so that cases involving loss of product can be solved easier. A cheap photo-resistor could be used to log each time the container is opened, so it can be determined at what point in the process thieves raided the container, or if the sender was being dishonest and claimed the container must have been robbed.
While light sensors are the only products that can give meaningful data regarding light, many other goods are sensitive to light. For example, paintings and photographs on paper and older works of art can be damaged due to exposure to sunlight, so it is important to know how much light they are exposed to. When shipping a work of art, a light sensor could be used to verify that it was not left in the sun for too long. A light sensor could also be used for siting the art to a permanent location.
Areas near the entrance or windows of a museum could have sunlight too harsh for particular materials, so a light sensor could be used to locate art appropriately. This is similar to the method for siting solar arrays on homes or in fields. Sunlight has important implications on agriculture, especially in the water-deprived American West. Different crops need different amounts of sunlight, so it is important to know which plots of land get the most exposure. As water supply becomes more strained in places like Utah, farmers have a financial and social obligation to limit water consumption, while also keeping their crops hydrated.
One tactic being adopted is to water crops in the afternoon or evening, to avoid the hot sun cooking off the water before the soil and plants can properly absorb it. A light sensor could be used to manage a sprinkler system automatically, only watering when the sun is not at its brightest. When coupled with other weather-monitoring equipment to gather data regarding temperature, pressure, and humidity, a system could not only water when the sun is dim, but also intelligently detect oncoming rain or clouds to optimize its watering schedule.
Now that you understand the mess of units that quantify light, we can start to understand how illuminance is determined using light sensors. Light sensors sometimes use a component called a photodiode to measure illuminance. When beams of light strike a photodiode, they have a tendency to knock electrons loose, causing an electric current to flow. The brighter the light, the stronger the electric current. The current can then be measured to return the illuminance of the light. If light-induced electric current sounds familiar, it is because this is the operating principle of the solar panels used to power road signs and homes.
Solar panels are basically very big photodiode light sensors. Another type of light sensor is the photo-resistor. Therefore, the sensors are typically sensitive in the range of 8 to 12 micrometers. The devices themselves are simple electronic components not unlike a photosensor. The infrared light bumps electrons off a substrate, and these electrons can be detected and amplified into a signal. You have probably noticed that your light is sensitive to motion, but not to a person who is standing still.
That's because the electronics package attached to the sensor is looking for a fairly rapid change in the amount of infrared energy it is seeing.
When a person walks by, the amount of infrared energy in the field of view changes rapidly and is easily detected. You do not want the sensor detecting slower changes, like the sidewalk cooling off at night. Your motion sensing light has a wide field of view because of the lens covering the sensor.
Infrared energy is a form of light , so you can focus and bend it with plastic lenses. But it's not like there is a 2-D array of sensors in there. There is a single or sometimes two sensors inside looking for changes in infrared energy. That is because glass is not very transparent to infrared energy. This, by the way, is the basis of a greenhouse. Light passes through the glass into the greenhouse and heats things up inside the greenhouse.
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