The discussion clarifies that the time it takes for light to turn on after flipping a switch is primarily determined by the propagation speed of the electrical field, which occurs at approximately two-thirds the speed of light. While the drift velocity of electrons is significantly slower, the immediate effect of the electrical field change allows for voltage to reach the light bulb within tens to hundreds of nanoseconds. Additionally, the type of light source affects the overall time until visible light is emitted, with LEDs responding more quickly than traditional lamps that require heating time.
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Oh, thank you! that clarifies a lot. One more question, regarding to the electrical field propagating "at a significant fraction of the speed of light", exactly how quickly is the propagation in comparison to the speed of light.Nugatory said:The change in the electrical field is what matters, and it propagates at a significant fraction of the speed of light - so we're talking maybe tens or hundreds of nanoseconds from switch closing to voltage across the filament of the light bulb.
The drift velocity of the electrons in the wire is much smaller, but that's something different. If you and I are holding opposite ends of a long metal rod and I pull on my end, you'll feel it almost immediately whether I pull quickly or slowly.