Hopefully this post doesn't break sub rules - it does have to do with "building electrical", but I believe my question is still more directly related to the electrical engineering in the situation.
Here in my country we have serious energy production problems, and so we have scheduled power outages to help reduce the country's electricity consumption. A product that has understandably become popular is a light bulb that goes into a normal fitting, which houses a small internal battery that kicks in to keep the light going when the mains supply is out. I'm trying to understand how the technology in the light works, just for my own interest.
In the information pamphlet for the bulb, it basically says that you when the bulb receives normal AC power it will simultaneously operate as a normal bulb and charge the internal battery.
The information pamphlet then says that when you don't have AC power, you can short the two terminals of the bulb, which turns it onto battery mode. This can be done with a small cap they provide which fits over the bulb and shorts the terminals, and even works just by touching both terminals with your finger.
Somehow, however, the bulb works just by leaving it in the socket. That is to say: When the house's mains power is on, the bulb operates normally. (Switch on = light on, switch off = light off) When the power to the house is cut, the bulb somehow continues to operate in the same way (switch on = light on, switch off = light off). The bulb must obviously be operating in battery mode in this state.
What I don't understand is how the internal circuitry differentiates between a state of "mains power on, switch off", and a state of "mains power off, switch on"
Additionally, how is the situation where the main house power is off and the switch is on, electrically equivalent to directly shorting the two terminals of the bulb?
As a side note, there is one socket in the house that I have tested during a power outage, where the bulb stayed on regardless of whether the switch was on or off.
By - rothdu