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Auto Night Lamp Circuits

We usually turn ON the lights in our houses and offices manually. We need to turn ON the lights only when it is dark. So, how will that be if we make a circuit which turns ON the lights automatically when it is dark? In this article, we shall see how to automatically turns ON our domestic Auto Night Lamp Circuits when it is dark.


  • Auto Night Lamp Using High Power LED
    • Circuit Diagram of Auto Intensity Control of LED Lights
    • Working
  • Intelligent Unambiguous Night Lamp Switcher
    • How to Operate this Night Lamp Switcher Circuit?

Auto Night Lamp Using High Power LED

An automated nighttime lighting system employing high-power LEDs is designed to activate the connected LED lights during nighttime hours and automatically deactivate them during daylight. High-power LEDs are gaining increasing popularity due to their numerous advantages over traditional filament bulbs and fluorescent lamps, such as producing superior-quality white light with greater intensity while consuming less energy.

This circuit serves as an illustrative example of how to regulate the brightness of a night lamp using high-power LEDs. The crucial component within the circuit responsible for detecting light is the light-dependent resistor (LDR). The LDR’s resistance varies in direct proportion to the amount of light it receives. As the light intensity incident on the LDR increases, the circuit’s resistance decreases, and conversely, the LDR’s resistance increases as the light intensity diminishes. Exploiting this characteristic of the LDR allows us to detect light and, consequently, control the behavior of the LEDs.

In this configuration, a total of twenty-five light-emitting diodes (LEDs) are organized into an array. Five LEDs are interconnected in series, and five such series-connected LED groups are then connected in parallel.

Circuit Diagram of Auto Intensity Control of LED Lights


During the saturation mode, transistors come into play, functioning as electronic switches. Specifically, the BC547 transistor, a versatile NPN transistor, is employed to control the LEDs. Notably, this transistor is equipped with a heat sink, a crucial component that facilitates the dissipation of heat generated during operation, enabling it to handle larger power loads effectively.

To power the entire circuit, including the LEDs, a 12V DC power source is typically utilized, with preference given to battery-based DC power supplies. However, it is also feasible to employ a regulated and rectified AC power source if desired.

In this configuration, high-powered white LEDs are employed, delivering illumination levels equivalent to those of standard fluorescent bulbs. This level of brightness is sufficient for various activities, including reading and everyday tasks. All components can be neatly assembled onto a printed circuit board, and the LEDs can be positioned in an orderly manner. For uniform light dispersion throughout your room, aim for approximately 1 cm spacing between the LEDs.

Intelligent Unambiguous Night Lamp Switcher

When designing a night lamp switcher, it is crucial to consider various factors to prevent potential damage to household equipment and lights. This circuit incorporates stringent measures to ensure that the activated lights remain safeguarded during the switching process.

Typically, a basic automatic night lamp switcher turns on the lights when darkness falls. However, there’s a potential issue to address. As darkness levels fluctuate, the circuit may receive rapid and alternating dark and light signals with brief time intervals. This scenario could lead to the circuit repeatedly switching the lights on and off at a high frequency, posing a risk of damaging our lights over a short period, be it minutes or hours. This repetitive switching occurs both in the evening and morning when the light intensity reaches a threshold that triggers the circuit to toggle the switch.

This circuit serves a dual purpose. It not only functions as a straightforward automatic light switching system but also effectively prevents the undesirable and frequent switching of devices. This aspect is often overlooked in similar circuits but is crucial for safeguarding our operational equipment, particularly the lights. Consequently, this circuit is aptly named the “intelligent unambiguous night lamp” as it employs intelligent control mechanisms to mitigate recurrent switching due to ambiguities in light levels.

Circuit Diagram for Unambiguous Night Lamp Switcher

Auto Night Lamp Circuits

How to Operate this Night Lamp Switcher Circuit?

Two photo-detecting components are employed to identify and distinguish between two distinct levels of light intensity within the circuit. In this setup, these photosensitive components take the form of Light Dependent Resistors (LDRs). The assessment of light intensity relies on both an LDR and an operational amplifier (op-amp) functioning as a comparator. The U1 IC 741 is responsible for detecting the first level of light intensity, while the U2 IC 741 identifies the second level. These two specific light intensities serve as criteria for determining when to activate or deactivate the lights, ensuring a clear and unambiguous signal.

These two light-detecting modules are interconnected in such a way that when the initial light intensity, referred to as “dark point 1,” is identified, the circuit triggers the relay, initiating the lights. Conversely, when both light-detecting modules sense light, the circuit deactivates the relay, ensuring there is no room for ambiguity. While simpler circuits exist for detecting darkness and illuminating the lights, most of them fall short in eliminating undesirable repetitive switching. This circuit effectively addresses and mitigates these unwanted switching effects.

Within the circuit, the U3 555 IC operates in the bistable mode, while the U4 IC serves as a buffer. The output from the first IC 741 is directed to the reset pin of the bistable IC, whereas the output from the second light-detecting module utilizing the IC 741 is fed to the set input of the bistable multivibrator.


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