Photoresistor unit measurement

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.

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

a quick search in the forum would give you some ideas

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.

At what wavelength?

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.

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

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


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