Photoresistor unit measurement

[andrealorenzetti123321]

Hi everyone, i am trying to read the brightness intensity of a light with a photoresistor in series with a 2kHom reisistor and when i read from the analogRead a number between 0 and 1023 but I does not understand what this value means and what is the unit measurement of this value.
In addition I tried to change the resistor in series and i get other values at the same conditions so i think that this value is realted to the voltage splitter.

I want to convert the value that i get into something like lumens.

[Idahowalker]

Using words like "arduino measure light intensity" in an internet search would yield some results that should be interesting.

[J-M-L]

a quick search in the forum would give you some ideas

Using LDR (photoresistor) to mesure lumen

Hey people, i want to mesure the amount of lumen with a ldr. I also have a 10k resistor. How can i transfrer the data from analgRead(); to the amount of lumen? note: lux is often confused with lumen, but lux is amount of lumen per square Great thanks if you have an answer for me! (link or propper code would be nice)

[dlloyd]

The datasheet for your LDR should have some useful information with graphs like "resistance as a function of illumination".

I think this Adafruit Learning System about Photocells shows what you're looking for.

[anon57585045]

@andrealorenzetti123321

I want to convert the value that i get into something like lumens.

At what wavelength?

[red_car]

Usually a photo resistor is used in a circuit like below. As the light changes, so does the resistance, and therefore the voltage at Vout.

and you typically are measuring Vout with an analog input pin.

Analog pin values are expressed as a comparison between the voltage received and a reference voltage (Aref)... this is typically 5v (if you're using an Uno for example).

So at 5v you will get a reading of 1023.. and at 0v you will get 0.

[jremington]

@andrealorenzetti123321

I want to convert the value that i get into something like lumens.

Do that by comparing the output of the Arduino device to that of a calibrated light meter, for a range of illumination levels. That will give you enough data to fit a calibration curve.

The curve will be valid only for the type of illumination you use (fluorescent and incandescent illumination are very different).

General overview of sensor calibration: Why Calibrate? | Calibrating Sensors | Adafruit Learning System

[MarkT]

If you want to measure light a photodiode is much more stable and reliable component than a photoresistor.

[johnerrington]

Using Operational Amplifiers in your Arduino project

4: Using Op Amps: A Practical example Measuring light level with a photodiode Photodiodes are used in many every day electronic devices such as cameras, smoke detectors, burglar alarms, safety equipment, medical applications, CD players and surveying instruments. They can be used to detect a wide range of electromagnetic radiation, from infra-red through the visible to ultraviolet and even x-rays. They aren't just for visible light. How they work When a photon (a bit of light or other EM wav…