Light Dependent Resistors (LDRs), also called photoresistors, have a resistance that changes based on the amount of light falling on them. The LDRs that I have are the ones that are commonly included in basic electronics components kits.
I assume you already know
Based on my LCR meter testing, they have the property of…
- Very bright light = almost 0Ω of resistance
- Very dark = Over 200MΩ (two hundred million ohms)
I suggest that the LDR always be in series with other resistance based on the supply voltage. The minimum circuit resistance will then be about the value of the other resistance. A parallel resistor can also be used to make sure there is never too much resistance.
More details about parallel resistors. Resistors connected in parallel
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