Providing Smart Technology Solutions


The name of this project is “Dark Lamp.” I designed this device for one of my friend Darbar. The Dark Lamp automatically lights when it finds dark. Let’s have a look at its picture.

The Dark Lamp

The Dark Lamp

I did a similar thing approximately 3 years ago, when I was in my 3rd semester of engineering, but it was anonymous. The designed was raw and simple having few components like LDR (which sense light), a transistor, few resistances and a LED for glowing in the dark. Let me show you the circuit diagram.

lamp corrected b

The working of the circuit is simple, when there is presence of light, the resistance of the LRD becomes low resulting in decrease in the amount of the base current. Thus the transistor reaches it’s cut off state stopping the flow of current in led. But when there is dark, the resistance of the LRD increases, increasing the amount of base current which makes the transistor ON and hence making the led to glow.

The above circuit is very simple but has certain limitations, especially it is not fit for driving high power LED’s. There is some leakage current in the cut off state of the transistor, which makes the led glow (very dim) when it should be perfectly off.

I kept that circuit in my closet and thought to use it somewhere. Now after a long time, one of my friend Darbar asked me to give this circuit to him. He is a school teacher, and he wanted that circuit to show to his students. So, I tried finding the circuit but it was misplaced somewhere. So, I decided to make a new and more advanced circuit for him.

First I want to show you all some pictures of dark lamp.




The ON/OFF Switch

The ON/OFF Switch

The red case is from an electronic lamp which was sold in the local market some years back. That lamp consisted of two high power led’s which get its power from a 9 v battery, having a resistance (for potential drop) and a on/off switch in series. I used this casing to fit my newly designed into it.

In my new circuit, I added one more transistor in cascade with the first one, thus forming a sort of darlington pair. It increases its gain and makes a sharp cut off for the led. The circuit is shown below.

The circuit diagram

The circuit diagram

The source voltage of 3.7v is provided by a small battery from a Tata Walky phone in my house. The battery was a scrap for the phone as it was giving a back up of 3 to 4 minutes only, but it works well with the dark lamp because it requires a very small amount of current to work. Amazingly it gives a very good back up, which is  4 to 5 days when I kept it permanently on(the led was off during day, but on in night).

You might be thinking about that black structure coming out from one side of the lamp. It is charger socket, used for charging the battery from a nokia charger. It is a female part which is compatible with nokia charger. I was having a spare converter for the charger cable, which is used to charge other phone with same nokia charger. That’s what I used here.

This circuit is more efficient than the previous one and does not have the problem of leakage current. You can watch the working of the Dark Lamp on YouTube from the link given below.

Hope you liked my lamp. Don’t forget to comment your ideas and what you think about this project …


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This entry was posted on December 18, 2012 by in Projects and tagged .

Physical Computing Mini-Projects


fun and learning with electronics


Providing Smart Technology Solutions

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