In this tutorial I'm going to show you how to build a really simple, light sensor, this uses an LDR.

What is an LDR

A Light Dependent Resistor (LDR) is a device whose resistance decrease with the respect to the light incident on it, it is also called photo-resistor.

This project can be used to detect whether it is day or night depending on the light intensity, you may need an arduino to make it more accurate and stable, but this is a really simple and fun project to build before actually moving into the arduino side of stuff.

Step 1: Tools and Components

All that you need for this project is -

BC547 transistor
LDR
LED
10K resistor
Breadboard

All the parts can be easily found at a local hardware store, or in any microcontroller starter kit.

Step 2: Circuit

The circuit is really very simple, it has just 4 components and no soldering skills are required to assemble it. All you need to do is follow the circuit above.

Step 3: Finishing

After assembling the circuit power on the circuit using a 3v coin cell or an arduino. As you take a light source towards the LDR the brightness of the LED increases, in other words, as the intensity of light across the LDR increases the resistance decreases and intern the base current along the BC547 increases, leading to an increase in the brightness of the LED.