Plug Socket with Emergency Lights

A plug socket with embedded emergency lighting, on the front of the plug socket. These are low voltage long-lasting LEDs that will illuminate when the mains electrical supply is removed.
The plug socket has an internally mounted charging circuit board, this is powered via the plug sockets main 230vac power supply terminals. The bright white light emitting diodes used for the emergency lighting is powered via the 3.7V rechargeable battery and only switch on when the power to the socket is lost.


LED Socket

The appliance operates similarly to the existing socket until it detects the power is removed when it automatically switches to battery operation and illuminates the bright light emitting diodes.
The rechargeable battery enables the light emitting diodes to stay on independently for up to a minimum of three hours or until the electrical power returns.

The idea was brought about after seeing the 24-storey Grenfell Tower fire which broke out on 14 June 2017. When a fire occures the electrical supply normally fails and if emergency light power sockets were installed, then you would have illumination close to the floor in a smoke filled area.


Benefits for socket emergency lighting.

Can be installed in grade listed buildings and provides the property with constant lighting, making it safe for people within the premises to evacuate calmly in the case of a fire, even if mains power is affected.

Emergency Light closer to the floor can reduce working time or money lost in trying to sort out situations if the mains power does fail.

If a fire occurs and there is a blackout, emergency lighting will make it easier to leave the building safely and calmly for everyone in the premises, the emergency light socket improves the emergency lighting in hotel corridors and rooms.

Due to their energy efficiency and environmental benefits, LEDs are safer and can save money in the long term.
LEDs are more efficient than incandescent bulbs
They waste very little energy as heat, unlike most light sources They can light up quickly and can be turned on and off frequently
LEDs are less fragile and have longer lifespans
They are less toxic because they do not contain mercury

BG Emergency Light Socket
BG Emergency Light
Emergency Safety Light
Emergency Light Socket PCB
MK Emergency Light Socket PCB
MK Emergency Light Socket PCB
Light Socket with emergency lights

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Type of battery

The battery used in this circuit is a 3.7v Li-ion battery 2600mAh.
Charging current in this circuit is 5.9mA, which is acceptable for slow charging since this circuit is for emergency lighting.
The 3.6V COB (LED strip is 3 Watts in power, so a 2600mAh battery at 3.6VDC = 9 Wh (Wh = mAh × V / 1000) this is 3 hours.

The above is NEVER actually true unless the battery is perfect. It is just an approximation supplied by the manufacturer of the battery pack (or cell) that this should be the expected performance.

So we install 2 X 2600 mAh batteries (5200 mAh) per socket, so total light duration is approximatly 19 Wh, which is over 6 hours of illumination, certainly enough for 3 hours as per the regulations BS 5266-1.

Emergency Light 3.7V Battery

LED / Resistor Calculation
Light Socket Circuit Circuit

Further Information

A power socket with emergency light, comprising of a power socket front switched or unswitched with a circuit board behind the socket front, a rechargeable battery and emergency light emitting diodes embedded into the socket front.

The internally mounted circuit board being provided with an external power from the sockets power supply input terminals, the rechargeable battery and the emergency light emitting diodes being in electric connection with the circuit board respectively; when the power line is connected to the socket, the emergency lights are in an off state, not illuminated; when the power line is disconnected from the external socket, fuse tripped or power cut, the emergency lights are in an on / lighted state.

The main advantage of installing emergency lighting is that your building will never be in darkness.

If an incident does occur it is crucial to make it as easy as possible for the occupants to make their way out quickly and safely through the designated escape routes.

Transistor Info


The power socket cover has the function of emergency lighting as well as providing power supply to appliances, enabling the emergency lights to be powered and light up when the socket mains power supply is unexpectedly cut off.

The emergency lamp circuit charges the 3.7v battery using the 230V AC electric line, when the 230V AC power is removed, the Light Emitting Diodes (COB) will illuminate automatically.

Working voltage: 1A, 250V
Working temperature: -15 to 40 C
UK 3 pin socket output: 13A, 250V
Fits any standard back box (minimum depth of 35mm)

If your property is in an area that suffers from a disrupted power supply then emergency lighting is definitely something to consider.

A typical high-power LED will realise 10 years maintenance free service when used for 12 hours every day, thus saving the maintenance costs of replacing 20 new filament lamps over the 10 year life span and the environmental cost of their disposal.


Technical Information

A 820nF (0.82uF) 250 or 400 volt AC capacitor is dropping the 230 volt AC (Tested 242.4 VAC) to low volt AC (Tested 21.8 VAC).
X Rated capacitor 0.82uf 250 or 400 Volt AC - X=1/{2xPIx50x0.82x(1/1,000,000)} = 38818.278 Ohms or 38.8 Kilo ohms. 230V/38.8 = 5.92mA

Bleeder resistor 270R 0.25W is used to remove the stored current from the C2 (0.82uF) 250 VAC capacitor.

BR IN4007 D1 through D4 rectifies the low AC to DC.

The capacitor 470uF 16V or 25V makes the DC ripple free (Tested 4.1 VDC).

This S9012 PNP transistor in TO-92 package is perfect for switching applications and switches power from the 3.7 volt battery to the light emitting diodes (COB - Circuit On Board).

Zener Diode is commonly used as a voltage regulator. Being a diode normally operated in the reverse bias and at the breakdown voltage, the zener diode allows the current to keep the voltage across the diode close to the zener breakdown 4.7 volts. Therefore it protects other devices against voltage pulses.

The 1K resistor is put in the base to limit the current as too much base current can destroy the transistor. A resistor is often used in series with the base of a transistor to limit base current. Without limiting base current you run the risk of damaging your transistor. Normally you will see 1K in the base, with 5V this gives you a base current of 5mA (I=V/R), which given a gain of 100 will not saturate at collector currents of 500mA. We want the transistor to be saturated, (turned on). So only a few mA are needed to turn a transistor on, hence a resistor is put in the base to limit the current.

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What Is Emergency Lighting?

Emergency lighting is battery powered lighting which will switch on and illuminate when the power is cut from the mains. This is usually for the people inside the building to find their way out of the building in a safe manner. Guidelines now exist which mean all new larger buildings must have the correct emergency lighting fitted whilst older buildings must retro-fit emergency lighting to ensure the building is as safe as possible.

Did you know UK legislation around emergency lighting is stronger in the UK than some other European countries?

In the UK we call for a minimum duration of three hours for emergency lighting if premises are not expected to be evacuated immediately, under the UK guidance document BS 5266-1 Emergency lighting –Part 1: Code of practice for the emergency lighting of premises.
In Europe they call for a minimum duration of one hour under the European Standards BS EN 1838:2013, lighting application – emergency lighting.

The UK Guidance document states the following:

‘A minimum duration of three hours should be used for emergency lighting if premises are not expected to be evacuated immediately in the event of a supply failure, such as sleeping accommodation or places of entertainment, or if the premises are expected to be reoccupied when the supply is restored without waiting for batteries to recharge.

A minimum duration of one hour should be used only if the premises are expected to be evacuated immediately on supply failure and not reoccupied until full capacity has been restored to the batteries.’

It is imperative that as a UK company you comply with the UK Guidelines set out above. By doing so, it means a building can be re-entered after there has been some kind of mains failure as there is still significant emergency lighting in place to meet the minimum requirements. The European standards mean that even if there is a five minute failure the building can not be re-entered as you would not meet the one hour minimum requirement.

What Buildings Am I Likely To See Emergency Lighting In?

All buildings which have a large footfall or are reliant on artificial lighting are obliged to have emergency lighting installed as a legal requirement. This is usually so the people inside can find their way out in the event of an emergency. Hotels, theatres, cinemas, apartments, flats, warehousing, retail shops, pubs and restaurants are just some of the places you will find emergency lighting.

Stairwells and exit routes are the places which are most likely to be illuminated when the power is cut along with first aid areas, refuge points and fire equipment areas.

What Is The Difference Between Maintained & Non-Maintained?

When looking for the emergency lighting fitting you require, you are likely to come across the terms 'maintained' and 'non-maintained'. These phrases are terminology usually associated with emergency lighting products, but what is the difference?

Maintained fittings are ones which can be operated with a lighting controller (such as a switch) and can be left permanently on or can just operate when there is a power cut.

Non maintained fittings will not illuminate unless there is a power cut, this is the emergency socket type we supply.

What Types Of Emergency Lighting Are There?

There are a variety of different types of emergency lighting which are available to suit whatever lighting need you may have. The most traditional type of emergency lighting are the internal and external bulkhead emergency fittings. These usually have a polycarbonate body and tray which houses all the components and most of these will operate for three hours without any mains power and will recharge when the mains power has been restored.

There are a variety of different shapes, however the most popular by far are the circular and rectangular shaped bulkheads which will stretch from 8W to 28W usually. In recent times, more decorative products have hit the market. Interior and exterior bulkheads which can be purchased with emergency gear inside so they will light when there is a power cut.

LED emergency lighting is now starting to become very popular thanks to its energy saving benefits. A lot of illuminated exit signs are now LED and are virtually maintenance free thanks to the fact the LEDs in the fitting will last for around 30,000 hours without needing to be replaced.

20mA LED Resistor Calculation

LED Type Forward Voltage Qty Max current Ohms Hours with 2AH Battery
Standard Size - T1 ¾ 5mm 3.2v-3.4v 5 100mA 5 Ohms 20 Hours
Standard Size - T1 ¾ 5mm 3.2v 5 100mA 5 Ohms 20 Hours
Standard Size - T1 ¾ 5mm 2.7v 10 200mA 5 Ohms 10 Hours
Standard Size - T1 ¾ 5mm 2.2v 15 300mA 5 Ohms 6.67 Hours
Standard Size - T1 ¾ 5mm 1.7v 20 400mA 5 Ohms 5 Hours
Our sockets have fitted a 3W COB (Chip On Board) rigid LED (Light Emmiting Diode) strip with 16 LEDs and a color temperature 6000-6500K, Pure white. The dimensions are Length 60mm X Width 8mm X Thickness 1mm.

Characteristics of the bipolar transistor S9012

Type - p-n-p
Collector-Emitter Voltage: -25 V
Collector-Base Voltage: -40 V
Emitter-Base Voltage: -5 V
Collector Current: -0.5 A
Collector Dissipation - 0.625 W
DC Current Gain (hfe) - 64 to 300
Transition Frequency - 150 MHz
Operating and Storage Junction Temperature Range -55 to +150 °C
Package - TO-92

Pin Configuration (Pinout)

The S9012 is manufactured in a plastic TO-92 case. When looking at the flat side with the leads pointed downward, the three leads emerging from the transistor are, from left to right, the emitter, base, and collector leads.

Classification of hFE

S9012 can have a current gain anywhere between 64 and 300. The gain of a S9012D will be in the range from 64 to 91, S9012E - range from 78 to 112, S9012F - range from 96 to 135, S9012G - range from 112 to 166, S9012H - range from 144 to 202, S9012I - range from 190 to 300.

Replacement and equivalent transistor for S9012

You can replace S9012 with 2SA708, 2SA709, BC527, BC528, KSA708, KSP55, KSP56, KSP92, KSP93, MPS3702, MPS4354, MPS6652, MPS6652G, MPSA92, MPSA93, MPSW51, MPSW51A, MPSW51AG, MPSW51G, MPSW55, MPSW55G, MPSW56, MPSW56G, MPSW92, MPSW92G, PN4354, ZTX554, ZTX555, ZTX556, ZTX557

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