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Arduino project · Light sensing · Easy

Dark-Activated LED Bar

As the room gets darker, more LEDs switch on, one more at each level.

What you will learn

  • How to build several light levels from one sensor
  • How thresholds work
  • Why the lower limits come later

How it works

The first LED lights below 60 percent light, the second below 40 percent and the third below 20 percent. In bright light all are off, and in the dark all three are on.

Try this next

  • Add hysteresis so the LEDs do not flicker at the limits.
  • Add a relay for a real lamp.
  • Use a bar of 8 LEDs.

The simulator program and explanation on this page are original. The idea follows a classic Arduino project that students have built for years.

1Choose your Arduino board
2Build the circuit
Parts: sensors and actuators (tap to show or hide)

Try the inputs (virtual sensors)

Pins (you can change them)

PartArduino pin (change it here)How to wire it

Every wire, one by one

Red rail = 5 V from the Arduino 5V pin. Black rail = GND. The coloured wires carry signals. Match the wire colours on the drawing to this list.

#ColourFrom (part and leg)To
3Define the sequence

Steps run from top to bottom, then start again. While the simulation runs, the active step is highlighted in green.

4Arduino code





5Parts list and where to buy


Quantities come from the parts you added. The store links open a search for that item on Robu.in, Amazon.in and ThinkRobotics, so you always see what is in stock today. Check the model, voltage and price before you order.


#ItemQtySearch termBuy / compare



6Export








The PDF has the circuit sketch, pin table, every wire, sequence, full code, the parts list with store links, do’s and don’ts for each part, and the safety notes. The project file lets you come back and keep editing.



7Learn: do’s, don’ts, cautions and tips





In the real world
A path of lights for the dark
When daylight fades the row of lamps lights up.
Tip: use the gold tab at the bottom of the circuit drawing to pull the real-world view up over the Arduino board. Your parts stay visible above it, so you can press a button and watch the real scene react.