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Emergency Light Using a Flashlight Bulb

In this write up we discuss the making of a simple emergency lamp using a 3V/6V flashlight bulb.

Though it's the world LEDs today, an ordinary flashlight bulb can also be considered a useful light emitting candidate especially because it's much to configure than an LED.

The shown circuit diagram is quite simple to understand, a PNP transistor is used as the primary switching device.

A straight forward power supply provides the power to the circuit when mains is available.

Simulation and Working

As long as power is present, the transistor T1 remains positively biased and therefore remains switched OFF.

This inhibits battery power from entering the bulb and keeps it switched OFF.

The mains power is also utilized for charging the involved battery via the diode D2 and the current limiting resistor R1.

However, the moment AC mains fails, T1 is instantly forward biased, it conducts and allows the battery power to pass through it, which ultimately turns ON the bulb and the emergency light.

The entire unit may be adjusted inside a standard AC/DC adapter box and plugged IN directly in to an existing socket.

The bulb should be kept protruding outside the box so that the illumination reaches the external surrounding amply.

Parts List

R1 = 470 Ohms,

R2 = 1K,

C2 = 100uF/25V,

Bulb = Small Flashlight Bulb,

Battery = 6V, Rechargeable Type,

Transformer = 0-9V, 500 mA

 The Design and Schematic

automatic emergency lamp using flashlight bulb

Need Help? Please leave a comment, I'll get back soon with a reply!


  1. Dear sir,
    i want circuit for inverter using cheaper cost for fan and cfl bulb using as a load please send me circuit for my mail

  2. Dear Lakshminarayan,

    you can try the following design:

  3. good afternoon sir,i thanked you for your support regarding projects on circuits.actually i would like to build the above emergency light circuit using flash light,however i want to use a power supply or battery which is less than 6V as u have mentioned,for example a baterry of maximum 4volts or less using bulb.if it is possible i am requesting u the circuit diagram and what will b the effect on the brightness of the surrounding at a voltage around 4V or les

  4. Hi Musa, if you intend to use a 4V battery, then you may prefer an LED instead of an incandescent can use a 1 watt LED with a 2 ohm series resistor...this will allow you to get a lot off illumination without doing any modifications in the above design....

    or if you plan to use a bulb then simply use a 3V flashlight bulb and make sure to put a 1N4007 diode in series in between the collector of the transistor and the bulb.


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