# How to Use a Photoresistor (or Photocell) - Arduino Tutorial

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A photoresistor or photocell is a light-controlled variable resistor. The resistance of a photoresistor decreases with increasing incident light intensity. A photoresistor can be applied in light-sensitive detector circuits, and light- and dark-activated switching circuits. It's also called light-dependent resistor (LDR).

In this tutorial you will learn how to use a photoresistor with and without arduino uno.

So, let's get started!

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## Step 1: How to Use Photoresistor

Let's see how a photoresistor react in light. Build the circuit above and notice how led brightness change.

The resistance value becomes smaller when there is much light in the room. So in the dark the led remains off because the resistance has become very big.

The Arduino will help us to reverse this situation, let's see how in next step.

## Step 2: The Circuit

You will need:

• Arduino uno
• LED
• 220 Ohm & 10 KOhm resistors
• Photoresistror

## Step 3: The Code

Here's the 'led & photoresistor' code, embedded using codebender!

How it works:

• Read analog value from photoresistor/photocell
• Check if value is bigger than e.g. 25
• Send command to turn on/off the led

Try downloading the codebender plugin and clicking on the Run on Arduino button to program your Arduino with this sketch. And that's it, you've programmed your Arduino board!

You can keep playing with that by clicking the "Edit" button and start making your own modifications to the code.

For example, try to change "25" value and see how it changes the program.

## Step 4: Well Done!

You have successfully completed one more Arduino "How to" tutorial and you learned how to use a photoresistor!

I hope you liked this, let me know in the comments.

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## 13 Discussions

Sorry,but the program isn't going to get cuted and paseted,and the ''run on

arduino'' button isn't working .could you tell me please how to get it working?

thank u very much for make it simple

are resistors imp.

Hello,

I'm new to arduino, had to replace the 10 KOhm with a 1 KOhm

With 1KOhm:

if (value > 25) led stays off

50: led on if i cover the photoresistor

100: led on at 2 or 3 mm from the photoresistor

With 330 Ohm:

100: led on if i put my hand between photoresistor and window (source light)

Thanks a lot,

Very fun :)

How would I code this so I could see the output's power? I'm using analogRead and serial.print, but the analog read keeps saying 1023, even when I put my hand over the photoresister.

I am having the same problem. Did you ever figure it out?

I thought the proper name for these was an LDR (light dependant resistor)

I m an instructable noob

How do you do that box in the intro page

hi im quite new to arduino and i have a question about voice recognition module v3.1