There are a lot of circuits that once you switch on a light, the light will be turned off automatically after sometimes.

Most circuits do not consume too much power during light off. However the standby circuit still consumes little current.

This circuit uses a relay to cut the power completely after time out, such that no electricity is consumed during standby.

Step 1: The Circuit

Three parts in the diagram:
1. LED light
- LED in series with one 200ohm resistor

2. timer by 555
- the 1k, 33k resistors and 470uf capacitor will turn pin 3 to ground for around 10 seconds

3. relay
- when pin 3 is low, transistor will switch on so relay close and circuit is on
- when pin 3 is high, transistor will switch off
- hence relay will open and circuit is off

The flow logic is like this:
- when you press button to turn on the ciruit, LED is on and timer is on
- even when you release the button, as the timer is on, the relay remains close so electricity goes through relay to the LED
- when timer is off, relay losts power so relay is open and the circuit is disconnected from battery
- LED is then off

Step 2: The Material

LED and 200ohm resisitor

555, 1k and 33k resistors, 470uf capacitor
- choose different resistors nd capacitor for differnet timer setting

1k resistor, npn transistor (I used 9013), 3v or 5v relay

4.5v battery

Step 3: The Deliverable

As shown, you can put the circuit on breadboard as I did.

I don't have a button so I used a wire to touch the positive end of battery to switch on.

The circuit will keep light on for around 10 seconds then you will hear a tak sound from relay and the light will be off.

When off, zero power will be consumed.

That is all. Enjoy !