In the dark, the current through an LDR is lower than in the light, assuming the same voltage is applied.

How an LDR behaves

  • An LDR (light-dependent resistor) has a very high resistance in the dark, often in the range of megaohms or more.
  • In bright light, its resistance drops dramatically, sometimes to a few hundred ohms or less.

Because current III through a resistor at a given voltage VVV is given by Ohm’s law, I=VRI=\frac{V}{R}I=RV​, a higher resistance in the dark means a smaller current, and a lower resistance in the light means a larger current.

Quick mental picture

  • Dark: Huge resistance → very little current flows.
  • Light: Small resistance → current increases a lot.

So if you keep the circuit the same and only change the light level, the LDR carries less current in the dark and more current in the light.

In many automatic night-light circuits, the LDR is arranged in a divider so that when it goes high resistance in the dark, the voltage at another component (like a transistor or relay) rises and turns a lamp on, but the current through the LDR itself is still lower than in bright light.

Information gathered from public forums or data available on the internet and portrayed here.