LDR night light

Thread Starter


Joined Jan 18, 2005
Hi there i have just taken apart a night light which automatically comes on in the dark due to the LDR.

I was wondering how it works, the circuit is very small and is comprised from a vers small LDR , 4 resistors,a terminal to connect with the bulb and another one which connects to a pin on the plug, and also there is a blach thing consisting of three terminal wires (i thought it might be a transistor but im not sure can anyone tell me what it is):

Also can you make things clear for me by telling me how it works, I think ( this is where i get confused);
An LDR decreases resistance when light increases and conversely when light falls the resistance increases, so i thought if the resistance increases in the dark which prohibits the current/voltage going to the bulb i wouldnt think the light would come on in the dark, and as tere is low resistance when its light i would have expected the bulb to light up allowin the current to flow to the bulb. I also have another strange theory, that black thing with the 3 terminal wires which i believed to be a transistor, i thought (i could be wrong please let me know) i thought that as it could be a transistor ans the base has to be 0.6v+ with respect to the collector and the emitter, when it is klight the there is too much current more than o.6 v so the lamp wont light but when its dark and the resistance increases there will be 0.6v so it will power the transistor switching on the light.

I know i have written a lot but i really need help, thankyou for your time