Question

Hello, Rabbi,
I’m not asking this question provocatively, but genuinely out of a desire to know.
I read that the ruling not to use electricity came from the period when electricity and the light bulb were invented. Incandescent bulbs had two filaments, and an actual spark was created. With an LED bulb there is no such thing at all, so no fire is ignited, not even a spark. Also, it is permitted to use electrical devices that were left on from before the Sabbath, like a refrigerator or plasma screens in synagogues. So a cellphone should also be kosher, even though it runs on a battery and is always on, and even if it isn’t on and you turn it on—what is the problem at all? Where does this come from?