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Solar automatic night light | Solar auto on-off night lamp

Hello engineers, Sometimes we need a little or less light is some parts of our home during the whole night. Areas like our lawn / our Garden area/parking lot during the whole night time. Also, we want to save electricity and energy for that, So, today I am going to discuss a Solar automatic night light or Solar garden night lamp. This circuit can provide a maximum of 4 watts of power and is easy and yet effective and reliable. So let’s discuss our Solar automatic night light or let’s say Solar automatic night light /dark detector light.

Solar rechargeable automatic night lamp circuit

solar automatic night light

Materials and components

  • Solar panel 12v 5watts/10watts
  • D1,D4 1N5400-2pcs
  • D2, D3 1N5351BRL-2pcs
  • D5, D6, D7 LEDs 1 Watt -3pcs[I suggest use 2 pcs to get better brightness/but if you are using 12v lithium battery pack then it’s alright.]
  • LDR1 LDR -1pcs
  • R2 160K-1pcs
  • Q1, Q2 TIP122 -1pcs
  • C1 2200uf-1pcs
  • C2 100uf-1pcs
  • Battery 12v lithium-ion 2000-4000mah battery pack or or lead-acid 12V 2ah- 4.5ah

The circuit above is using a 12v solar panel rated up to 5-10watts for charging the 12v battery source during the day time. The batteries can be of 12v lithium-ion battery pack or 12v lead acid or SMF or Gell cell battery.

The charging is governed by 14v Zener they will keep battery level topped up to 12.8-13V. The battery is continuously charged during day time but it cant be overcharged since the solar panel will be able to provide voltage more than batteries initial voltage only when sunlight is in good amount and sunlight focus is also good. As I have suggested battery up to 12v 2000mah-4000mah lithium battery pack, so the battery total power is around 40Wh(according to 4000mah) and the panel is only let’s say 10w providing voltage more than 12v for sure in good sunlight. So that would also take 4-5 hours to charge the battery and this is only the time till the sunlight’s focus on the panel will be good. So any mah or ah value battery will not be overcharged.

The LDR’s sensitivity is set by R2 160k due to lights starts from 6:30 pm evening. The transistors Q1 and Q2 drives the 1 watt LEDs.

How LDR does control the Circuit? How does actually circuit work?

An LDR is a photoresistor whose resistance is least when the light incident over it is at the high intensity and its resistance is highest when kept in dark. So, during the day time, when daylight is falling over the LDR, its resistance is least approx.100ohms which makes the transistors’ Q1 and Q2 base get shorted to ground and this makes transistor kept turned off because of getting grounded and the LEDs are not glowing and the battery is just charging.

During the absence of daylight, the LDR isn’t getting any light and this increases LDR’s resistance to the maximum. This makes a strong barrier between the transistor’s base and ground and the base gets power input via160k resistor. This turns the transistors Q1 and Q2 ON making the LEDs glow brightly during the night via battery.


Use proper small heat sinks for transistor Q1 and Q2 which are TIP122 transistors. Also, make sure that the placement of LDR must be such that only daylight/sunlight can fall over it and not the output of operating LEDs.Also, make sure that the circuit is waterproof(arranged in a kind of box or some kind of arrangement.

For people using TIP122 first time make sure that the pinouts of TIP122 arent arranged as the normal transistor, instead, they are 1.base,2collector and 3. emitter.refer to google if you are new to electronics projects and MOSFETs.

Below I have added a small video of simulation and showing how actually this circuit works.

The video

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Aabhishek Sharma is a Computer Science Engineer and a Digital Marketing Trainer and Consultant. Aabhishek Sharma also loves working on Electronics Projects and working with microcontrollers and Designing Home automation Gadgets.

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