how to reverse a photoresistor
Looks like i found a solution for your question,,,

If you used the LDR in the feedback resistor chain of an opamp, then that ought to work as you require...

You'd need to pay close attention fixed resistance(10K) though...probably a bit of experimentation would be in order depending upon LDR behaviour,

You can also exchange LDR place with that 10k resistance,

Solution 2(WITH SINGLE BJT!):







simulate this circuit &ndash; Schematic created using CircuitLab

The concept here is simple you connect 2 series resistance (1Pot to experiment) such the voltage drop is sufficient to turn on the transistor form the source at the same time allowing most of the current to flow through LED ,voltage at node 1 should be barely enough to turn on the transistor.

When LDR is on as you might be knowing it offers low resistance and current chooses path of least resistance hence transistor will be OFF so will be the LED,,

You might want to consider to add a base resistance but is optional i think so.

hope this helps