Here's a variation on Les' circuit, using the other half of the 393 (dual comparator IC) instead of the BC337 to provide current regulation, and with hysteresis added to the first comparator so that passing clouds etc don't cause false switching of the light. Trimmers allow adjustment of hysteresis, dark/light threshold and LED current.
View attachment 94418
The blue graph simulates LDR resistance. For 'kV' read 'kΩ'.
Note that, as with Les's circuit, a small heatsink will probably be needed for the FET (as well as a
large heatsink for the LED). A 100uF cap across the supply, as Les shows, would be advisable.