Some people need instructions so that when the device burns out, they can find out what they did wrong.
Making a switch backlight with an LED yourself is not difficult at all. An extremely simple circuit can be assembled literally “on the knee” within a few minutes. But, if you don’t want everything to end with fireworks and burnt wiring, read this article carefully.
Scheme for connecting an LED to a switch in an apartment
Circuit diagram and appearance of the switch
As you can see, the device consists of only two elements - a current-limiting resistor and a light source.
Many people who are not related to radio electronics may be confused by this scheme. After all, we put the LED in a 220V AC switch, although the LED itself is designed for a voltage of 2-12V DC. And the main lamp, in theory, should also glow with this connection.
How and why does it work?
Let's remember the school physics course:
- Voltage is the potential difference at the two ends of the conductor. The higher the voltage, the faster electrons travel through the wires.
- Current strength - electron density in a conductor. When an electrical circuit encounters a section with high resistance along the path of electrons, some of them give up their energy to this section.
When the current (electron flux density) is significantly greater than the area can handle, the excess energy is converted into heat. If there were no resistor in front of the diode, the current passing through it would be many times greater than its rated parameters, turning the diode crystal into a cloud. In this circuit, the resistor acts as a valve, cutting off most of the current. Current will also flow through the incandescent lamp itself, but its strength is so small that the coil will not heat up.
Calculation of circuit parameters
Selecting a resistor for the LED. In this formula, the network voltage is taken as 320V, since it is necessary to take into account not the nominal parameter, but the effective peak voltage.
Selecting a resistor How to make a backlight for a switch
The main purpose of an LED backlit switch circuit is to limit the amount of current flowing through the LED. For a diode, it doesn’t matter at what speed electrons pass through it, it will take its “portion” and convert it into a glow. If the electron flux density is higher than its throughput, the excess will be released in the form of heat, melting the crystal.
Installation LED into 220V switch, diagram:
Options for how to connect an LED Option 1
This connection method will work, but for a very short time, a few milliseconds, until the filament of the incandescent lamp lights up. With this connection, the circuit current will be calculated based on the needs of the lamp, exceeding the needs of the LED by hundreds of times. This is the wrong option.
Option 2
This is already a viable option. Current-limiting resistor R1 will reduce the current to the required value. For a regular 20 mA LED, the resistor value should be:
(320V-3V)/0.02A≈16 kOhm and power 0.25-0.5W.
To increase the service life of the backlight and reduce the heating of the resistor, it is better to increase the resistance parameters by 3-4 times. Such a circuit can be seen if you disassemble a cheap Chinese switch with an LED. There is no reverse current protection, which does not contribute to the long life of such a device.
Option 3
Turning on the diode with reverse polarity protects the LED from reverse half-wave. This is important if there are powerful devices on the network line: washing machine, boiler, electric kettle. You can use any small-sized diode with a voltage of up to 500-1000 volts.
Examples of calculations
Since our task is only to illuminate the switch and achieve maximum viability, we take the LED current 30% of the nominal - 6mA
Resistor current limiter
Usd=3.5V, Isd=20mA (0.02A) - We do the calculation at 6mA (0.006A);
R1= (330-3.5) /0.006=55000 Ohm (55 kOhm). In order to reduce heating, the resistor value can be doubled to 100 kOhm.
Resistor power P=Ur1 I=327 0.006=2W.
It is better to mirror a 1000V diode in parallel with the LED.
Capacitive current limiter
Instead of a resistor, you can use a high-voltage capacitor; R1 is necessary for the self-discharge of capacitor C1. The capacitive circuit does not heat up.
C1=Rc/(2 π £)=50kOhm/(2 3,14 50Hz)=150uF; C1=150uF*500V;
R1=0.5-1 MOhm;
The diode is the same as in the previous design.
If the switch is intended for an energy-saving lamp, it is better to replace the LED with a neon lamp, the donor of which will be the starter of the fluorescent lamp. Classical circuits, due to half-wave damping, can cause flickering of “energy-saving” devices. The connection principle remains the same, but due to the higher rated current, about 100 mA, the resistor or capacitance (on a neon light bulb) should be increased to 500-600 kOhm.
Application area
- switch circuit with LED backlight;
- power indicator in a portable extension cord;
- miniature night light;
- lighting for socket.
If desired, you can connect an LED strip, but only on a capacitive limiter after careful recalculation.
This is what the LED backlight looks like 
How to connect using a live example Below is a diagram of how to connect a switch with an LED. Connection instructions
- Before installing the LED circuit in the switch, make sure that the switch is disconnected from the “phase”. This can be done using a simple tester screwdriver.
- Check the quality of insulation of all connecting contacts. Bridging exposed wires will, at best, damage the lighting circuit, and, at worst, damage the wiring in the apartment.
- If necessary, you can make a mounting hole for the LED in a plastic part so that it evenly illuminates the switch button.
- We assemble the resulting structure and enjoy the result.
If we use the resistor option, it is worth experimenting with the resistance parameters. The diode can “start” with 2V or 3V; accordingly, in the second, the resistor value can be reduced.
Do not forget that in such devices only the electron density is limited; the voltage remains the same and is still dangerous for living organisms.
Everyone has encountered a situation where it is necessary to turn on the lighting in a completely dark room. Even if the location of the switch is known, it can be very difficult to cope with the task. And in an unfamiliar environment, searches can take a long time. By using an illuminated switch, you can avoid such situations.
Description
Entering an unlit room, everyone intuitively tries to find the switch to turn on the light. This procedure is often accompanied by falling objects. The most unpleasant thing is the brown coating that remains on the wallpaper around the switch and along the entire “path” to it. It is almost impossible to wash off these marks without damaging the wall covering. An illuminated switch will help avoid damage to the interior and nerves.
How does such a device differ from a conventional lighting device? The main feature is only the presence of a special light indicator, which allows you to immediately find the location of the desired object in the dark. In appearance, the device does not differ from conventional switches. A significant advantage of such a device is the use of an LED light bulb as an indicator, which saves energy consumption.
Varieties
The modern market offers many different types of devices equipped with a light beacon. This allows each buyer to choose the most suitable version of the device. Switches differ not only in external data, but also in design features. In the electrical store you can find the following types of devices:
- keyboard models - are easy to install and affordable;
- pass-through switches - allow you to activate one of the two lamps connected to them (used to illuminate long corridors and large rooms);
- push-button switch - instead of keys, such a device has buttons of various shapes.
All of the above can be either with or without a backlight indicator. One-, two- and three-key models are popular.
Principle of operation
Before connecting the backlit switch, you need to understand how the device works. As has already been found out, such a device differs from a conventional switch in one detail - the presence of an indicator. This function can be performed by LED or neon bulbs. The circuitry of such a device provides for a phase wire break. If there is a backlight, the diode lamp simply connects the wire in the off position.
Why doesn't the main lighting turn on when the indicator is on? The answer to this question is quite simple. The device system is equipped with a resistor that has current-limiting properties. The resistance of the lamp filament is much less (almost zero) than that of the indicator, so the operating voltage is supplied to the switch backlight lamp with a resistor connected in series. This causes the indicator to light up. If there is no light bulb in the backlight circuit or it is inoperative, the indicator will also not be able to light due to a broken power circuit.
Connection
Installing an illuminated switch is a fairly simple task.
The whole process will take no more than half an hour if you follow the following recommendations:
- First of all, you need to turn off the power supply. You can de-energize only the room in which the installation will take place, or the entire room.
- We remove the outdated device. To do this, first remove the keys, and then the frame itself. At the end, unscrew the fastenings of the device and take out the internal elements.
- Slightly loosen the fastening of the contacts and release the device.
- On the back of the new backlit switch there should be a connection diagram, following which we carry out installation. Installation is carried out according to the same principle as dismantling, only in reverse order.
- The last step is to test the performance of the device and the backlight. To do this, just turn on the switch.
Which lamps are suitable for indicator switches?
How to connect a backlit switch so that there are no problems during operation? First of all, you should find out which lamps such electrical accessories are compatible with.
Many note that when using indicator switches and energy-saving lamps, problems arise due to their incompatibility. The reason lies in the design of the lamps themselves. To charge the capacitor of an energy-saving lamp, even a small voltage that passes through the diode is enough. This causes the starter to operate and the lights to turn on.
The triggering mechanism is repeated many times, which leads to flickering. Incorrect use of the lighting device negatively affects its service life.
We are looking for a way out of the situation
How to connect an illuminated switch in combination with an energy-saving lamp? Experts recommend installing an additional resistor in this case. The small current that charged the rectifier capacitor (with the lights off) will flow through the 2 W shunt resistor.
There are also LED lamps on sale that are compatible with switches. They already have a built-in shunt resistor, or soft start. Such a device does not flicker when the capacitor is discharged, but turns on within a few seconds.
Illuminated switches Legrand
A switch is a mandatory element of the electrical network, which must be reliable and of high quality. The devices of the French company Legrand are considered one of the best. The manufacturer makes the base of the device from galvanized steel for better mounting of the switch to the wall. During operation, such a base does not deform.
Double illuminated switches of the Valena series from the French manufacturer are the most popular. They have a simple connection diagram and can be used in rooms with high humidity. The company offers electrical accessories in such series as Etika, Soliroc, Celiane, Cariva, Galea Life, Kaptika.
Viko switches
The Turkish company Viko offers high-quality electrical accessories and is one of the largest suppliers of such products. Viko backlit switches from the Carmen series have elegant, smooth shapes and are made of cream or white plastic. A light touch is enough to activate the design.
The switches have a red indicator light, which is appreciated by consumers. Devices from the Karre series, which have one or two keys and a light controller (dimmer), are also suitable for indoor installation.
Today you can find a switch with LED backlight in almost every home. Using such a switch in the dark is much more convenient, but with the advent of fluorescent and LED lamps, problems began to arise with these “convenient” devices.
Some modern lamps connected through a backlit wall switch flicker even though the light is off. The blinking effect, which is unpleasant for the eye, occurs due to a closed electrical circuit formed by a resistor with an LED (or a resistor and a neon bulb) and a power converter circuit for an LED or fluorescent lamp.
There are several ways to get rid of blinking in a 220V lamp, more on that already. In this article we will consider the simplest and most reliable option in more detail. It consists of removing the backlight from the switch. So how do you turn off the backlight in the switch? First things first.
Preparatory stage
If you have not encountered replacing or installing backlit switches before, you will have to prepare a little and think through your actions. In general, measures to remove a neon light bulb or LED can be divided into two stages:
- removing voltage from live wires;
- preparation of the necessary tools.
The first point is to de-energize the room in which the illuminated switch is located. To do this, the circuit breaker handle must be moved to the “off” position. In some houses, instead of them, fuses (plugs) are installed, which will have to be unscrewed. If the phase and neutral wires are connected to different machines, then for complete safety, turn off both machines (remove both plugs).
The essence of the second stage is to avoid unnecessary fuss in search of the missing tool during work. To remove the backlit switch and turn off the backlight, you will need: an indicator screwdriver, a heavy-duty flathead screwdriver, wire cutters and a knife.
Turning off the backlight
Initially, all actions for dismantling a neon lamp or LED completely coincide with the work of replacing a conventional switch:
- blackout of a room or apartment;
- removing the decorative on/off key from the latches, slightly prying it off on both sides;
- unscrewing the mounting bolts and removing the device from the mounting box;
- Use an indicator screwdriver to double-check the wire contacts for the absence of voltage;
- Having remembered the connection diagrams, the wires are disconnected.
Then you need to carefully examine the design of the illuminated switch and find the latches that hold the two parts of the housing together. By opening the latches, the switch will be divided into two halves. In one of them a resistor is soldered or screwed to a neon light bulb or LED.
All that remains is to carefully cut the terminals of the radio components, remove them and assemble the switch without backlighting in the reverse order.
There are backlit switches on sale, but rarely does anyone get around to replacing one that is already installed without backlighting and is still in good working order.
After spending half an hour, anyone who wants to improve the comfort of night life will be able to add lighting to the switches in their apartment on their own, even without the skills of an electrician.
You can install the backlight switch according to one of the proposed schemes. The circuits differ not only in configuration, but also in technical characteristics. For example, an LED circuit may not work if the luminaire contains LED lamps. And energy-saving lamps may flicker or glow faintly in the dark. Let us consider in detail the advantages and disadvantages of each of the schemes.
Switch illumination circuit based on LED and resistance
Currently, lighting switches are usually equipped with LEDs, which are included in the switch according to the electrical diagram below.
When the switch is in the “Off” position, the current passes through resistance R1, then through the LED VD2, which lights up. Diode VD1 protects VD2 from reverse voltage breakdown. R1 of any type with a power of more than 1 W, rated from 100 to 150 kOhm. With the R1 rating indicated on the diagram, the current flows about 3 mA, which is quite enough for a clearly visible glow in the dark. If the LED glow is insufficient, then the resistance value must be reduced. VD1 of any type, VD2 of any type and color of light. In order to understand the theory and independently calculate the size and power of the resistor, you need to read the article “The Law of Current Strength”.
An LED switch illumination circuit can be installed if the lamp uses incandescent light bulbs. If there are compact fluorescent (energy-saving) ones, then it is possible that in the dark you may notice their faint glow or blinking. If the lamp is equipped with LED bulbs, then the backlight made according to this scheme may not even work, since the resistance of the LED bulb is very high and a current of sufficient strength for the LED to glow may not be created. In the dark, the LED light may glow faintly. The scheme is very simple, but has a big drawback: it consumes a lot of electricity, about 1 kW×hour per month. This is what the assembled circuit looks like.
All that remains is to connect the ends that point down to the switch terminals. If you did not make any mistakes during installation, the circuit will work immediately. I specifically posted a photo of the twists for those who do not have the opportunity to solder the connections with a soldering iron. For reliability and safety, you still need to solder the twists and cover the bare wires and resistor with electrical tape.
Switch illumination circuit using an LED and a capacitor
To increase the efficiency of the backlight in the switch, you can install an additional capacitor in the electrical circuit, while reducing the value of resistor R1 to 100 Ohms.
This circuit differs from the above by using capacitor C1 as a current-limiting element instead of a resistor. R1 here performs the function of limiting the capacitor charge current. Resistance R1 can be used from 100 to 500 Ohms with a power of 0.25 W. Instead of a simple diode VD1, you can install an LED, the same as VD2. The efficiency of the circuit will not change, and both LEDs will shine at once with the same brightness.
The advantage of a circuit with a capacitor is low energy consumption, about 0.05 kW×hour per month. The disadvantages of the scheme are the same as those presented above and, in addition, large overall dimensions.
Switch illumination circuit for a neon light bulb (neon)
The backlighting circuit for a switch on a neon light bulb (neon) is devoid of the disadvantages inherent in the LED backlighting circuits presented above. This switch illumination scheme is suitable for chandelier switches and any other types of lamps, with both incandescent light bulbs and energy-saving fluorescent and LED lamps installed in them.
When the switch is open, current flows through resistance R1, the discharge lamp HG1 and it lights up. R1 of any type with a power of more than 0.25 W, rated from 0.5 to 1.0 MOhm.
In the photo you see the assembled switch illumination circuit, which couldn’t be simpler. It is enough to connect a resistor in series with a neon light bulb of any type and the circuit is ready.
Where to get a neon light bulb
Neon gas-discharge bulbs (neons) are presented in a wide range and you can use any of them available. Please note that on the left in the photo there is a gas-discharge light bulb with a 200 kOhm resistor, removed from a failed computer extension cord switch, which is also called the Pilot. It can be successfully installed in any switch without the additional hassle of finding components. The same light bulbs with a resistor are installed in electric kettles and other electrical appliances to indicate the on state. In the center of the photograph, a Small-sized Thyratron (triode) with a Cold Cathode MTX-90 unexpectedly appeared. To be fair, I’ll say that the MTX-90 thyratron has been shining in my sconce for decades.
Neon bulbs (neons) surround us almost everywhere. Are you surprised? All older fluorescent light fixtures use a starter, which is a real neon light bulb housed in a cylindrical housing. In order to remove it from the lamp body, you need to turn the cylinder slightly counterclockwise. There are as many starters as there are fluorescent lamps in a luminaire. In the starter, a capacitor is also connected in parallel to the neon lamp; it serves to suppress interference and is not needed in the manufacture of the indicator.
If the starter is taken from an old lamp, before using a neon bulb, do not be lazy to check it. Before installation, you must connect the light bulb according to the above diagram. It is better to take a neon from a new starter, since in old ones the glass of the bulb bulb from the inside is usually covered with a dark coating and the glow will be less visible. A light bulb from a starter can be successfully used to make your own phase indicator.
A ready-made lighting kit for installation in a wall switch can be taken from a faulty modern electric kettle. As a rule, most models have a water heating indicator. The indicator is a neon light bulb with a current-limiting resistor connected in series and this circuit is connected in parallel to the heating element. If you have a faulty electric kettle lying around in your household, then a neon light bulb with a resistor can be removed from it and mounted in the switch.
The photo shows three neon lights from electric kettles. As you can see, they shine quite brightly, so in the dark they will be visible in the switch from a great distance.
If you look closely at the insulating tubes placed at the junction of the terminals of the neon light bulb with the wires, you will notice a thickening on one of the tubes. A current-limiting resistor is located at this location. If you cut the tube lengthwise, a picture will open, as in this photo.
Step-by-step instructions for installing in a backlight switch
When working on the switch, you must turn off the power supply!
Neon light bulbs come with a base and without a base, in which the leads come directly from the glass bulb. Therefore, the method of their installation is somewhat different.
Installing a neon light bulb with flexible leads into a switch
As a rule, the length of the leads of a neon light bulb (neon) or LED is not enough for direct connection to the switch terminals and therefore they must be extended with a piece of copper wire. For these purposes, both single-core and stranded wire of any cross-section are suitable. The best way to connect the wire to the terminal is by soldering.
Before soldering, the terminals of the neon light bulb and the ends of the conductor must be cleaned of oxides and tinned with solder using a soldering iron. Then join to a length of at least 5 mm and solder.
Then the soldering point and the terminal of the neon light bulb need to be insulated by putting an insulating tube on them. You can simply wrap a couple of turns of insulating tape.
For ease of soldering, the end of the soldered conductor is formed into a ring using pliers and secured to the switch terminal.
The keys or covers of wall switches are usually made of white plastic and the light from a neon bulb (neon) or LED passes through them well. It is enough to make the switch key visible in the dark. Therefore, there is no need to drill a hole in the switch opposite the backlight installation location.
An insulating tube is also placed on the soldered resistor or it is insulated with insulating tape. The end of the output is formed into a ring and secured to the second terminal of the switch.
The switch illumination circuit is installed, the switch is connected to the electrical wiring, all that remains is to install the key and the work can be considered complete.
Installing a neon light bulb with a socket into a switch
It is not advisable to use a socket for illumination, since the service life of a neon light bulb (neon) is longer than the service life of the switch, and there is not enough space in the box. Therefore, it is more advisable to connect the base to the circuit using soldering.
To do this, you need to remove the insulation from the wires, tin the bare ends and make small loops. Then solder the light bulb terminals on the base to the soldering points.
A resistor is soldered to the wire extending from the central contact of the base at a distance of 2-3 cm. The resistor leads need to be shortened and wire loops made at the ends. A wire is also soldered to the second terminal of the resistor.
The threaded part of the base and the resistor must be insulated. This can be done using heat-shrinkable tubing, insulating tape, or the method I suggest.
Many good polyvinyl chloride (PVC) tubing is often used to insulate wires. To prevent the tube section (cambric) from slipping, the internal diameters should be slightly smaller than the insulated solder. There are always difficulties in finding a cambric of suitable diameter.
But if you hold the cambric for about 15 minutes in acetone, it becomes elastic and can be easily put on a part that is one and a half times larger than its internal diameter. This is how I insulated light bulbs in a homemade New Year's garland in the distant past.
After the acetone evaporates, the cambric again returns to its original size and tightly fits the lamp base. It is no longer possible to remove the cambric unless it is re-soaked with acetone. This insulation method is similar to heat-shrinkable tubing, but no heating is required.
After the preparatory work, the backlight is placed in the switch box and connected to its contacts.
If there is not enough space to place a resistor or you do not have the required power at hand, then the resistor can be replaced with several of lower power, connecting them in series or in parallel.
When resistors of the same resistance are connected in series, the power dissipated on one resistor will be equal to the calculated power divided by the number of resistors, and their value will decrease and will be equal to the calculated value divided by the number of resistors. For example, according to calculations, a resistor with a power of 1 watt and a nominal value of 100 kOhm is required. 1 kOhm = 1000 Ohm. This resistor can be replaced with two 0.5-watt, 50-kOhm resistors connected in series.
When connecting resistors of the same resistance in parallel, the power is calculated as with a series connection, and the value of each resistor must be equal to the calculated value multiplied by the number of resistors connected in parallel. For example, to replace one 100 kOhm resistor with three, the resistance of each must be 300 kOhm.
When installing the circuit, connect the resistor (capacitor) only to the phase wire of the switch. Since the currents flowing through the circuit elements do not exceed several milliamps, there are no special requirements for the quality of the contacts. If the box with the switch in which the backlight will be mounted is metal, then it is necessary to exclude the possibility of the current-carrying conductors touching its walls.
It is impossible to spoil anything when installing the backlight in a wall switch, since the lamp itself is a current limiter. The worst thing that can happen is the failure of the mounted elements if serious mistakes are made. For example, turn on the LED without a current-limiting resistor, or the resistor value is mistakenly taken to be 100 ohms instead of 100 kOhm.
Calculator for calculation
current limiting resistor parameters
When installing it yourself in a backlight switch on an LED or neon light bulb, it is necessary to determine the size and power of the current-limiting resistance. The calculation can be done using formulas, but it is much more convenient to calculate the resistor parameters using a special calculator. Just enter the parameters and get the finished result. The calculator can also be useful for selecting a resistor in a factory-made backlit switch in case the resistor fails.
Reference. On an LED the voltage drop is in the range of 1.5-2 V, on a neon bulb it drops 40-80 V. The required minimum current at which the LED is guaranteed to glow is 2 mA, for a neon bulb - 0.1 mA. This data can be used for calculations on a calculator if the parameters of an LED or neon bulb are unknown.
When choosing a resistance, it becomes necessary to determine its value by color marking. An online calculator will help solve this issue.
Illuminated switches for electrical appliances
Illuminated switches are often installed in switches on carriers and extension cords, heaters and other electrical appliances. They usually have a neon light bulb with resistors built into them. I once had to repair a Pilot type extension cord in which the switch control key fell out and cracked.
When I disassembled the switch, I did not find a current-limiting resistor, which I was very surprised by. Neon bulbs must not be connected to a 220 V electrical network without current limitation. It will fail immediately. On the left photo is a view of the key from the side where the neon light bulb is installed, and on the right, the reverse side of the same switch key.
I measured the resistance between the spring and the terminal of the neon light bulb, it was 150 kOhm. This switch used an interesting design solution: two 150 kOhm resistors were installed in the key holes and a spring pressed them to the terminals of the neon light bulb, ensuring reliable contact. The springs themselves exert pressure on the movable contacts in the switch, from which, when the switch is in the On position, power is supplied to the neon light bulb.
Using a backlight circuit for display
The backlight of the switch performs another additional useful function - it indicates the functionality of the switch and the serviceability of the light bulb. If the backlight works, but the light does not turn on, then the switch is faulty. If the backlight does not work, then the light bulb has burned out.
Any of the above presented circuit options can be used to indicate the health of devices or electrical circuits. For example, if you connect it in parallel with a fuse, then if it blows, the indicator will light up. If an electrical appliance does not have a standard on indicator, then by connecting the indicator immediately after the switch, you can always see whether the appliance is on. When installed in a socket (connected parallel to the current-carrying wires), you will know whether the socket is energized or not.
When choosing switches for lighting residential premises, we are always faced with a dilemma: should we buy a regular light switch, or one with backlighting? Any manufacturer, including the popular legrand, offers the same models, both with and without an indicator.
What is an illuminated switch for? This may sound strange, but for the cleanliness of the walls. Every time we feel the keys in the dark, we gradually grease the walls around us and create scuffs on the covering. The price difference is small, but connecting an illuminated switch obviously provides certain advantages. Why do many buyers prefer traditional models?
The fact is that there are common “horror stories” and myths about the negative aspects of backlighting
“Horror stories” and myths about the illuminated switch
To understand the so-called "problem", let's look at the different types of indication. It comes in neon and LED. There is no fundamental difference in power consumption; both schemes consume no more than 1 W of power. Neons come in two colors: orange (red) or green, depending on the gas in the bulb. The LED can be of any color, even dynamically changing hue (RGB).
Now about the myths:
- Additional electricity consumption. This statement is partly true. The LED backlight circuit consumes about 1 W of energy. In a month, it accumulates 0.5–0.7 kilowatt/hour. That is, you will have to pay a couple of rubles for comfort (from each switch). Neon lamps have similar costs. There, the energy is spent mainly on the limiting resistor.
- « We installed the backlight - now the switched off lamps glow in the dark!" And it is true. Old-style lamps (incandescent and halogen) go out regularly when turned off. But no one uses them anymore. The problem concerns economical fluorescent gas-discharge lamps (they flash periodically), and LED lamps with an inexpensive control circuit (weak glow).
The first option is gradually becoming irrelevant.
Information about this is in the instructions for the lamp.
If you have to come to terms with the first myth (additional energy consumption): you just pay a small amount for convenience, then the second “problem” has several solutions. You will learn about this from our material.
Connection
First, let's look at the design of the backlit switch. The operating principle is based on Ohm's laws. When lines with different resistances are connected in parallel, electric current flows along the path of least resistance.
Regardless of the indicator used (neon lamp or LED), the connection circuit has a high resistance. This is provided by a limiting resistor. The backlit switch circuit is shown in the illustration:
When contacts L and L1 are closed, the backlight unit is bypassed and current flows through the switch contacts. The main lamp lights up.
When the switch is opened, the lamp serves as a normal conductor. A small current flows through it, sufficient to operate the backlight. If an incandescent lamp is used, the spiral does not glow at such a meager current. But with housekeepers and LED lamps the same problem arises. The control circuit (the so-called driver) starts at a small current, which is provided by the backlight connection circuit.
As an example, let's look at options for using backlights in Legrand products.
The backlight mode in the illustration is indicated by a picture of the month, the installation of a switch with operation indication is indicated by a picture of a light bulb.
A single-key switch with night illumination is connected according to the classical scheme: a light bulb on contacts L. To indicate operation, a working zero must be set to the backlight lamp.
Connecting a two-key switch is done in the same way. Each operating line has a separate indicator light. The circuit provides separate indication of the double switch, each backlight works for its own line.
The three-key switch works exactly the same way. There will only be three indicators. By the way, this is another argument for opponents of the backlight: a three-key switch in display mode spends 3 times more energy than a double switch.
It can also work with backlighting. Only the switching diagram will be different. The indicator is connected to those contacts that will be open when the key is in the “down” position. As a result, if you turn on the light with one of the “pass-throughs”, the backlight on it goes out.
When using the backlight as an indication of lamp operation, the indicator is connected to the lamp side, and a separate working zero is connected to it. Regardless of the position of the “feeders”, when the lighting is turned on, the indicator will light up.
Legrand sells backlight lamps separately. In essence, it is an ordinary LED with a quenching resistor and a freewheeling diode, packaged in a heat-shrinkable tube.
If you don’t want to overpay for the logo on the price tag, you can make a spare indicator yourself. The circuit is simple: in order to prevent reverse current from flowing through the LED element (we have alternating voltage in the network, the polarity changes with a frequency of 50 Hz), a reverse diode (type D226) is installed. And since the voltage drop across the LED is 2–3 volts (depending on the color), a current-limiting resistor is installed in the circuit. Diagram and part values in the illustration:
Any switch can be equipped with such an indicator, the main thing is that the light breaks through the plastic.
In fact, these are ordinary load resistors. They actually block unwanted light while using as much energy as a low-wattage incandescent lamp. That is, your lights are turned off, but the meter continues to wind.
To “make friends” between a backlit switch and LED (economical) lamps, you need a pass-through switch.
Yes, the connection circuit is more complicated (you will have to draw the neutral wire). But you have to pay for the comfort of use. Electricity consumption is minimal, power no more than 1 watt.
Video on the topic
