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Light sensor: how to save electricity and increase safety


Surely each of us had to look for a switch on the wall in a dark room. Well, if the floor is flat, and the switch is provided with a backlight. And how to be in a long dark room or on the stairs? Take a flashlight with you or leave the lighting on duty? But there are more modern and elegant solutions that do not require additional costs of electricity and allow you to turn on the light only when necessary. One of these solutions is a light sensor.

A light sensor or a motion sensor to turn on a light is a device that automatically turns on the light when it detects movement in the illuminated area. In addition to the inclusion of electricity, the device can be programmed for any other action, for example, turning on the siren, ventilation, heating or air conditioning, recording a video camera, sending notifications. The presence sensor to turn on the light has a higher sensitivity. Such devices are widely used in basements, garages, corridors, on stairs, at entrances, on the porch of a house. In short, in those places where people are often, but not for long. They are irreplaceable in security alarms.

The sensor is based on the analysis of the waves that it catches from the zone of action. Moreover, the sensor itself can also send waves. According to this principle, sensors can be divided into:

  • active, which emit a signal and record the reflected one (consist of a emitter and a receiver);
  • passive, which catch their own radiation of the object and not having a radiator.

Active sensors have a higher cost.

Ultrasonic sensors are active: the emitter emits waves with a frequency of 20 to 60 kHz, the receiver registers the parameters of the reflected waves. When a moving object appears in the range of the device, these parameters change and the sensor is triggered. Ultrasonic sensors have many advantages:

  • are inexpensive;
  • do not depend on air temperature, are not afraid of moisture and dust;
  • they work regardless of the material from which the moving object is made.

There are some disadvantages of ultrasonic sensors:

  • adversely affect some pets;
  • act on a small distance;
  • may not work if the object moves slowly and smoothly.

Thanks to these features, ultrasonic sensors are widely used in automatic parking systems for cars and control of "blind zones". In homes, they are comfortable in long corridors and on stairs.

Infrared sensors detect changes in thermal radiation from surrounding objects. They can be both active and passive.

Passive sensors pick up thermal radiation emanating from the object using optical devices (lenses or concave mirrors) and convert light energy into electrical energy. The device is triggered when the converted voltage exceeds a predetermined threshold.

Sensors of this type are active, the emitter emits electromagnetic waves with a frequency of 5.8 GHz. Due to the minimum wavelength, the device is characterized by high sensitivity and accuracy.

For microwave waves there are no barriers in the form of walls or furniture. This should be considered when designing. Microwave sensors are most often installed in non-residential premises that require enhanced security, for example, in museums, bank vaults, weapons storage areas or important documents. In an apartment or private house, it is appropriate to install a microwave sensor in a separate non-residential area that requires security.

The main parameters of motion sensors

  • Bipolar or tripolar. Simple bipolar sensors can only be connected in series with incandescent lamps, and luminaires of any kind can be connected to tripolar.
  • The working area or range is usually from 3 to 12 meters.
  • The magnitude of the detection angle in the horizontal plane varies from 60 to 360 degrees in different models. In the vertical plane, the detection angle is less - 15-20 degrees.
  • Rated power connected to the sensor. If the total load exceeds the capacity of the sensor, you need to put an intermediate relay or increase the number of sensors.
  • The sensor off delay is programmed so that the person has time to go through the entire illuminated area, even going out of the range of the device. The time is set from 5 seconds to 10-12 minutes.

Connecting a luminaire with a built-in light sensor is a snap, and with a new device there is usually an instruction for connection. Each device has a terminal consisting of three terminals:

  • L - phase input, connect to it the wire is red or brown. To avoid errors, you need to check the presence of a phase with a screwdriver indicator;
  • N - zero input for connecting the blue wire. The absence of a phase is also checked with a screwdriver indicator. Using a multimeter, you must check the voltage between zero and phase;
  • And - connection of the lamp. It may also be referred to as "L →", or simply "→". When connecting the lamps, check their total power and compare with the allowed power of the sensor.

On some devices there is a PE terminal, indicating protective grounding. This terminal must not be confused with zero input.

In some cases, it is necessary to automatically turn on and off the light when the ambient light changes. In this case, street lights can be equipped with day-night sensors. They consist of a photosensor and a starting electronic unit. Function as follows:

  1. When changing the intensity of light falling on the sensor sensor (photodiode, resistor), the resistance of the photocell changes.
  2. The signal from the photocell enters the starting electronic unit.
  3. The starting block works, turning on or off the lamp.

The photorelay can be replaced by a technical novelty - astrotimer. It differs from the photo relay by the presence of the built-in GPS-receiver. When you connect, you need to set the time and date, time of the year and season on it the astrotimer itself will determine. With the help of information from satellites for your region, the device will independently adjust to the time when it starts to get dark or dawn comes. Astrotimer has no false positives, as it is not affected by the weather, its location or interruptions in electricity.