Types of sensors in automatic control (PT1): Light Sensor

The light sensor is an important part of the residential lighting control system, which makes lighting in greenhouses, …

A light sensor, as its name implies, is a device used to detect light. There are many different types of light sensors, each operating in a different way. For example, a photocell or photoelectric cell changes its resistance when light comes in, which is a kind of light sensor, which is used in many consumer products to determine the intensity of light. A Charge-Coupled Device (CCD) is a device that converts light energy into electrical signals by means of optical diodes and microchips attached to the diodes, made from semiconductor molecules. . The CCD chip is used as a light sensor in digital cameras and night vision devices.
Devices containing light sensors have many uses in everyday science and life applications. A simple light sensor may be part of a security device, a safety alert device, such as an anti-theft alarm or a garage door opener. These devices usually operate by projecting a beam of light emanating from one sensor to another, if light is interrupted, an alarm or garage door will act according to the installation requirements. .
Many modern electronic devices, such as computers, cordless phones and TVs use ambient light sensors to automatically control the brightness of the screen, especially in low light conditions. Bright or high light. They can detect the light level in a room and control the increase or decrease in brightness to a greater degree of comfort for the user. The light sensor can also be used to automatically turn on the lights inside or outside a home or business office in the dark.
There are three common types of sensors, used to measure light for different applications.
Optical Sensors: Optical sensors are designed to mimic the reactions of the human eye. Optical sensors are often used in lighting applications for the user. The measurement unit of the optical sensor is usually expressed in lux, lumen, or foot-candle. Optical sensors are not particularly suitable for use in plantation applications as they may not provide an accurate indication of the spectrum produced by different light sources. In other words, although a light source can appear “pretty” bright, is perceived by the naked eye, but its spectrum may still be unsuitable for planting trees. However, optical sensors can be used to indicate fairly well on the intensity and uniformity of light in a plant when moving under illuminated foliage (for green systems). In the greenhouse).
The simplest optical sensor is the magnetic impedance [2]: the internal impedance of the photonic impedance (eg, 10 kΩ corresponding to 10 lux when measured by optical resistors LDR12mm-10K / 2M) when light The excitation stimulus and the huge increase (2 MΩ) when illuminated is not excited (the photoresist surface is darkened). Thanks to this resistor change, the photoelectric resistor (light sensor) is coupled to the appropriate electronic circuitry to create a switching / closing circuit, or a shift in each specific application, such as the system. Close / open lights, lighting control system in the greenhouse, …
Photodetector: Outdoor phototherapy is often designed to measure the solar radiation received from the entire hemisphere. The unit of measurement is usually watts per square meter per second (Wm-2). The optical fire gauge measurements can be used to support a wide range of decisions to regulate the greenhouse environment or to open / close residential lighting systems, or any other application. Any other use of sunlight.
Outdoor fireplaces can be used both outdoors and indoors, but it is not particularly useful in evaluating additional lighting sources for home-optimized solar radiation applications. With indoor radiation measurements (eg greenhouses), the use of a “black” optical firehose will result in better results than an outdoor flares.
PAR Sensor: PAR sensor or photoelectric radiation (PAR) sensor in the range of 400-700 nm. This sensor measures light in micromole units per square meter per second (μmol.m2.s-1). They are used primarily in gardening research applications to measure photosynthetic radiation in canopy, greenhouse, seed orchard and germination, and laboratory and light applications. In commercial greenhouses, the PAR sensor can be used to measure PAR values ​​at different points above and below the green canopy and / or check the uniformity of light when deploying the system. New lighting.

The remote sensing light for information to regulate the proper operation of the appropriate lighting fixture meets the requirements of shade, full darkness, or use of shade. Information from sensors in different locations can also be used in combination to activate lighting control based on actual measured values.
The fixed location of the light sensor should be located in an atypical shade or target light metering area. Power poles, dome roofs and canopy can be selected to install a fixed light sensor. Of course, always make sure that there are no obstructions blocking the sun’s rays. Indoor and outdoor sensors should be regularly inspected and cleaned as recommended by the manufacturer, as there may be obstructions, dirt, etc. In all situations, it is important to install The sensor is safe and horizontally. Most light sensors are required to be calibrated after two years or as recommended by the manufacturer.
Because the amount of sunlight received is influenced by all the variables of climate change, measurement information from the light sensor is an important element in the integrated lighting control system. Reading light, both instantaneous and cumulative, is used to assess the speed and extent of response required for environmentally responsible climate control, such as climate in the greenhouse. Because many environmental climate change factors and can be directly correlated with light, it is combined with other factors such as wind, temperature and humidity, so the climate control program Can be adjusted in relation to actual weather both in real time and in forecasting calculations. For example, when opening a “mixing” valve to supply heat into the room, the control system can change the settings related to the light energy. If the value of the light is increasing, the system can regulate the return of the energy to the hot water to prevent room temperature surges, and heat losses, if any (from two sources Hot water + solar) can be ignored. This is also true for ventilation, irrigation systems and any other activity that is affected by light.
It is estimated that energy consumption for lighting demand accounts for 20-40% of total energy consumption in buildings and commercial centers and accounts for 3-10% of total energy consumption in the industry. . Therefore, together with the solution to enhance user awareness, we need to apply advanced technology in lighting control system to reduce to the lowest power consumption. Technically, it is an alternative solution of replacing old, obsolete lighting equipment with advanced lighting equipment, consuming less power (today, it is the use of ultra-bright LEDs – age High brightness, good light quality, very low power consumption), and modernize the lighting control modules in each cluster, each level of automation (remote operation, automatic operation scheduled Optimal, according to the automatic identification of objects to turn on / off lighting …) based on the target energy saving electricity.
Automated lighting control solutions have been very successful and practical applications such as automatic lighting control systems for streets, residential areas, factories around the buildings. Just turn on / off the lighting but also automatically change the light output according to the density of the traffic participants / appear in the lighting area.
In today’s modern society, “smart” homes / apartments with automatic lighting detection and adjustment systems depend on the density / number of people and the intensity of light present in each room. Is commonly used. This system not only enables / disables, adjusts the lighting in each room when someone enters (with the PIR – pyroelectric infrared sensor) or / and when light is insufficient (by sensor But also link the lighting controls in the rooms together to adjust the lighting forecast for the other room (turn on the lights before the person arrives). The typical structure of this automatic lighting system is described in Figure 2. Each room is equipped with an HLCM lighting controller along with the number of lights determined according to the light demand of the room. These lighting controllers are interconnected by RF radio waves or by Modbus standard wired network.
Light is a special material, a form of energy that is both wave-like and particle-like. Therefore, the characteristics of light such as speed, frequency and wavelength can be measured completely. Sensors for light measurements are very diverse, but in applications in livelihoods or in the agro-industrial sector, optical sensors are still the most commonly used. Combined with semiconductor electronics, microcontroller technology, today, it is possible to design controllable light sensor integrated circuits that are useful for a variety of everyday applications. Day as well as in the field of agriculture and lighting industries. These automatic lighting control systems have a number of advantages not only in small, lightweight, low power consumption, but also in terms of reducing the amount of power consumed by the entire system.

[first]. Digital Addressable Lighting Interface,
[2]. Datasheer Ambient Light Sensor TEPT5700, Vishay Semiconductors
[3]. Alex Ryer, Light Measurement Handbook hydrocarbons, International Light Inc., 1998.

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