Electronic – What’s wrong with the basic light/dark detection circuit

circuit analysisdiodesldrled

I've just started playing with electronics, and wanted to make a light/dark detection circuit without using a transistor (they are too advanced for me at this moment.)

I decided to use these components:

  1. LED
  2. 10k Resister
  3. 9V battery
  4. LDR

I want my LED to turn off when I shine a light on the LDR. I also want my LED to turn on when I cover the LDR. But this does not happen. I'm not sure what is wrong.


simulate this circuit – Schematic created using CircuitLab

Best Answer

The circuit with LED and circuit with LDR are in parallel.

Assuming a normal 9V battery, the LDR won't have much effect on the LED, it would not shunt enough current to turn the LED off.