Light sensor (photo relay) for street lighting

Owners of private homes when improving the site is concerned with the question of how to make automatic switching on the light at dusk and turning it off at dawn. For this purpose, there are two devices – photo relay and astrotimer. The first device is simpler and cheaper, the second is more complicated and expensive. In more detail, let’s talk about photorelays for street lighting.

Device and principle of operation

This device has many names. The most common – photorelay, but they are also called photocell, light and twilight sensor, photosensor, photosensor, twilight or light-controlling switch, light sensor or day-night. In general, there are many names, but the essence of this does not change – the device allows you to automatically turn on the light at dusk and turn off at dawn.

The operation of the device is based on the ability of some elements to change their parameters under the influence of sunlight. Most often used photoresistors, phototransistors and photodiodes. In the evening, when the illumination decreases, the parameters of photosensitive elements begin to change. When the changes reach a certain value, the relay contacts close, supplying power to the connected load. At dawn, the changes are reversed, the contacts open and the light goes out.

Characteristics and selection

First of all, choose the voltage with which the light sensor will work: 220 V or 12 V. The next parameter is the protection class. Since the device is installed on the street, it should not be lower than IP44 (the numbers can be more, less – undesirable). This means that objects larger than 1 mm can not get inside the device, and also that water splashes are not terrible for it. The second thing you should pay attention to is the temperature mode of operation. Look for such options, which with a reserve overlap the average indicators in your region both for plus and minus temperatures.

Select a model of photorelay also need to be selected by the power of the lamps connected to it (output power) and load current. It can, of course, “pull” the load a little more, but there may be problems. So it is better to take even with some reserve. These were the mandatory parameters by which to choose a photo relay for street lighting. There are a few additional ones.

In some models there is an opportunity to adjust the threshold – to make the photosensor more or less sensitive. It is worth reducing the sensitivity when snow falls. In this case, the light reflected from the snow may be perceived as dawn. As a result, the light will turn on and off. This is unlikely to be a pleasant experience.

Pay attention to the sensitivity adjustment limits. They can be more or less. For example, the AWZ-30 photocell manufactured in Belarus has this parameter – 2-100 lux, the P02 photocell has the adjustment range of 10-100 lux.

Operation delay. What is the delay for? To exclude false switching on/off of light. For example, at night the light of a passing car headlight hits the photocell. If the delay of triggering is small, the light will be switched off. If it is sufficient – at least 5-10 seconds, this will not happen.

Choice of installation place

For correct operation of the photo relay it is important to choose its location correctly. It is necessary to take into account several factors:

As you can see, when organizing automatic lighting on the street, choosing a place to install the photorelay is not the easiest task. Sometimes you have to move it several times until you find an acceptable position. Often, if the light sensor is used to turn on the lamp on the pole, the photocoupler tries to place it there as well. This is not necessary and very inconvenient – you have to clean off dust or snow quite often and it is not very fun to climb the pole every time. The photoreluver itself can be placed on the wall of the house, for example, and the power cable can be pulled to the lamp. This is the most convenient option.

Wiring diagrams

The wiring diagram of a photoreluver for street lighting is simple: the input of the device leads phase and zero, from the output phase is fed to the load (lights), and zero (minus) to the load comes from the automatic machine or from the bus.

If you do everything according to the rules, the connection of wires should be done in the distribution (mounting box). Choose a sealed model for location on the street, mount in an accessible place. How to connect the photo sensor to lighting on the street in this case – in the diagram below.

If it is necessary to turn on / off a powerful lamp on the pole, in the design of which there are chokes, it is better to add a starter (contactor) to the scheme. It is designed for frequent switching on and off, normally tolerates inrush currents.

If the light should be turned on only at the time of a person’s presence (in the street toilet, near the gate), a motion sensor is added to the photorelay. In such a bundle, it is better to first put a photosensitive switch, and after it – a motion sensor. With this construction, the motion sensor will be triggered only in the dark time of day.

As you can see, the schemes are not complicated, it is quite possible to cope with your own hands.

Features of wiring

The photo relay of any manufacturer has three wires. One of them is red, another is blue (can be dark green) and the third can be any color, but usually black or brown. When wiring it is worth remembering:

• the red wire always goes to the lamps:
• to the blue (green) one connects the zero (neutral) from the supply cable;
• the black or brown is the phase.

If you look at all the above diagrams, you will see that they are drawn in compliance with these rules. That’s it, no more complications. By connecting the wires in this way (do not forget that the neutral wire should also be connected to the lamp) you will get a working circuit.

How to set up a photo relay for street lighting

You need to customize the light sensor after installation and connection to the network. To adjust the limits of operation in the lower part of the case there is a small plastic rotary disk. The sensitivity is set by turning it.

A little higher on the case there are arrows, which indicate which way to turn to increase and decrease the sensitivity of the photoreluver (left – to decrease, right – to increase).

To begin with, you set the lowest sensitivity – drive the regulator to the rightmost position. In the evening, when the illumination will be such that you decide that it is necessary to turn on the light, you start adjusting. You have to turn the regulator smoothly to the left until the light comes on. At this point you can consider that the adjustment of the photoreluver for street lighting is finished.

Astro timer

Astronomical timer (astrotimer) is another way to automate street lighting. The way it works is different from a photo relay, but it also turns the lights on in the evening and off in the morning. Control of the light on the street is based on time. This device contains data about what time it gets dark/light in each region in each season/day. When setting up the astro timer, you enter the GPS coordinates of its installation, set the date and the current time. The device works according to the program.

How is it more convenient?

• It does not depend on the weather. In the case of installing a photo relay, there is a high probability of false triggering – in cloudy weather, the light can be turned on in the early evening. If the light hits the photocoupler, it may turn off the lights in the middle of the night.
• The astro timer can be installed in the house, in the switchboard, anywhere. It does not need light.
• It is possible to shift the on/off time by 120-240 minutes (depending on the model) relative to the set time. That is, you yourself can set the time as you like.

The disadvantage is the high price. In any case, the models that are available in the retail network, cost quite a lot of money. But you can buy in China much cheaper, though how it will work is a question.