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

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!

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
• Breadboard
• 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
  -> value=analogRead(pResistor)

• 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.

There will be more of them, so make sure to click Follow button!

Comments

[roscoeberetta]

Please show the code.

[zaqili]

could you explain on why do you connect the bread board that way

[Neutrino_bucketlist]

I doubt anyone is still reading this in 2020, but here is my take on this.

If you set a global variable equal to A5, then hook up just the photoresistor (with a 10k resistor in series with the ground) and read the inputs with the serial monitor on a 1 second delay (so you can read the numbers and see what the high and low is). Once you know those numbers set the lightVal to 50 to 75 below the lowest number you saw, maybe out of 100 or so values.

Then do the if statement something like this, if(lightVal > lightCal -100 || lightVal == lightCal-100). At the end of the loop put in a 400ms delay. Those 2 settings with take pretty much all of the chatter out.

I hooked this circuit up to a relay module and wired in a 120v light since I plan on using this for my porch lights. That's why I had a "chatter".

[agent oo7]

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?

[MuhK]

thank u very much for make it simple

[yashb62]

are resistors imp.

[geraldlec]

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 :)

[sara33]

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.

[emmy99999]

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

[wenden_jason]

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

[zbot473]

Can you just read the Photoresistor output

[zbot473]

I m an instructable noob

How do you do that box in the intro page

[gaganvajra]

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

.can anybody help me please....

i need to know how to use the commands and what r the commands.......

[codebender_cc]

Hi! Just stay online and make sure that you have pressed the "Follow" button.

I will write a "How to" tutorial with this in the future.

[tinker2015]

hi im quite new to arduino and i have a question about photocells i was hoping you could help me with i need to stop/pause a sketch using a photocell when its detected a change in light how would i do this any help at all will be appreciated

[codebender_cc]

Hi! That is quite simple. Just use the part of code with " if " conditions.