LDR Output Unit

I am trying to make a project using LDR. Sir I was curious which type of Light sensor is the most sensitive. In exactly which unit it displays the LDR output in the graph (like 1.02 thousand in lighted or 25 when no light). what is the unit of 1.02 and 25?

@vaman040697 its most probably 1024 as i have seen before. pls do check with this. hope this might help you

Thanks a lot @malolanaravamuthan

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Hi @vaman040697
There are majorly 3 types of Light sensors:
PhotoTransisors, Photodiodes and photoresistors.

Coming to their Sensitivity, It follows the order:
PhotoTransisors > Photodiodes > photoresistors.

A Light Dependent Resistor(LDR) changes its value with intensity of light in its surroundings.
“Candela” is the unit of Luminous Intensity, However the at the output end we receive some analog values.
These values are “Relative” and have no units.
They just give an idea so that we can compare light and dark.
The output Values are the consequence of change in Voltage across LDR.


Thankyou @shaleengovil2000 for clearing my dout regarding the same topic.

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Regarding the output unit of the LDR, and how the value comes about, as mentioned it’s related to the voltage and resistance in the circuit…

But if the measurements of the ldr are relative how to use it for any purposes

The final output of the LDR is in an analog format which just shows the amount of voltage created.
How is this voltage created?
Well it is due to the light falling on the LDR and its intensity and therefore it helps to know the brightness of the light.

But if there is no reference value then how is a user supposed to know if a particular value is light or dark. Further without a scientific scale this device is practically useless

Yes you are right. This type of unit system is generally used for personal projects and hence the user just approximates the values. For example: if the value is less than 10 then it’s completely dark or covered.

Hi @chirayushchakraborty ,
Since every LDR is different, you have to check the reference values yourself! To do so, first put the setup in a completely dark room and note the reading. Then put it in the region of maximum light and take the reading. For some LDRs, resistance decreases exponentially as the brightness of the light increases. In any case, Resistance is inversely proportional to light intensity. Check out this article.