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    This is an LDR based emergency light that turns on a high watt White LED when there is darkness in the room. It can be used as a simple emergency lamp in the child’s room to avoid the panic situation in the event a sudden power failure.
    It gives ample light in the room.

    The circuit is too simple so that it can be enclosed in a small box. A 12 volt miniature battery is used to power the circuit. Two transistors T1 and T2 are used as electronic switches to turn on / off the white LED. When there is sufficient light in the room, LDR conducts so that the base of the PNP transistor T1becomes high and it remains off. T2 also remains off since its base is grounded. In this state, White LED remains off. When the light falling on the LDR decreases, it cease to conduct and T1 forward bias providing base current to T2. It then turns on and White LED switches on.

    Schematic of Mini Emergency Light Circuit

    emergency led light circuit

    White LED used in the circuit is 1 watt High bright Luxeon LED. Since 1 watt White LED consumes around 300 milli ampere current, it is better to switch off the lamp after few minutes to conserve battery power.

    attentionThe author D Mohankumar is not an active member anymore. Please take into consideration that the presented information might not be correct.
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    26 Responses to "Mini Emergency LED Light Circuit"

    1. lettttttt me try this…………….

    2. Hi,

      Please clarify the correct part number of T2.Is it BD139?
      Simply irresistible circuit.Thanks!

    3. T2 is BD 139.Sorry for the mistake. Diagram corrected

    4. To D. Mohankumar
      Sir i have some doubts regarding cordless headphons circuit.I would like to mail you the circuit along with doubts.Will you please give me your email id. I am B.E. student working on this project.

    5. if ican use 300 red leds which voltage each is 1.5v and connections is series so which smps we can use for this board and which resistors use in beteween leds

    6. wich smps and how much amps please send me on my email

    7. sir will you plz tell me what modification will done for operating on 9v high watt battery

    8. prasad try change the r1 and vr to little lower.
      step by step.

    9. sir what is the value of the LDR and R2, also 10 k in R1 is a potentionmeter?pls help

    10. is this working! any body plz help me

    11. pls response its not working the automation of t1 and t2 is not happening

    12. can we add other 2-3, 1 watt led ???
      and what will be the amount of vlg& current consumed by the above circuit !
      please help me!!!!!!!!!!!!!

    13. please sir this circuit is not working plz reply to my mail sir iam doing the project

    14. Sir, i want know cost of each component and what type of battery we have to use, is it a drycell or rechargable battery

    15. I think 33ohms resistor is not enough, 1 kohm resistor and normal LED is sufficient for that place.and power supply change to 5v.

      • This circuit is intended for use as an emergency light so it requires a higher light intensity, that is why a 1W led is used. You cannot use a regular 20 mA LED because it doesn’t provide enough illumination.

      • abbas ali says: on March 28, 2014 at 6:33 pm

        Mention the correct values for resistors and power LED should be used or not?

    16. @popescu marian will pls give the list of components required for this experiment!

    17. mention the values of resistors used and can’t we use one watt power LED?

    18. What is the value of resistor R2.

    19. sir,can you tell us how much this project costs????

    20. it is not working…plz help its my project

    21. Can this project work on 9v battery???

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