Turning off a led at daylight...

[Externet]

How to make a simple switch to turn off a led during daylight using only one transistor, jfet or mosfet, and a light dependent resistor ? No other components, besides the white led and a 3.5V cell ?
Is there a way to turn on at dusk, off at dawn with that minimum of components ?
Or, does a reverse coheficient LDR exists, low resistance when dark ?

 

[Venkadesh_M]

If a LDR behaves reversely it wont help you because you shdnt allow the load current through it....

You could do this well with a 555 IC

 

[betwixt]

There is no reliable way to do it without other components. The schematic in post #2 is as simple as it can be. You might get away with removing the resistor in series with the LED if the battery is unable to supply much current but I wouldn't advise it.

Brian.

 

[Externet]

Thanks, gentlemen.

If a LDR behaves reversely it wont help you because you shdnt allow the load current through it....

Unless, in theory, a reverse coheficient LDR ? :
(+)---------/\/\/\/--------------|>|-------------(-)

 

[Venkadesh_M]

Thanks, gentlemen.


Unless, in theory, a reverse coheficient LDR ? :
(+)---------/\/\/\/--------------|>|-------------(-)

I don think so....