Typically, when a 3-way switch only works when one switch is on, this is one of the most telltale indicators that the switch has gone bad (although this could also be the result of faulty or loose wiring). To diagnose the issue, toggle each switch until the light comes on. Once it’s on, toggle each switch separately again; the switch that doesn’t turn the light off is the bad switch. 

Just as fluorescent lights are more efficient than incandescent lights, LED lights are more efficient to run than fluorescent lights. The specifics will vary from product to product, but LED lights are typically twice as efficient as equivalent fluorescent lights. A 13-watt CFL bulb can replace a 60-watt incandescent bulb, but a 6- to 8-watt LED bulb can offer the same amount of brightness. Fluorescent lights offer about 50 lumens per watt, while LEDs offer about 100 lumens per watt. LED light bulbs typically last two to three times as long as CFL bulbs, too. 

Yes, if something sparks when you plug it in or turn it on, it's important to unplug it immediately. A spark from an electrical appliance or device could indicate a short circuit, damaged wiring, or other electrical problems that could cause electrical fires or electrical shock. By unplugging the appliance, you can reduce the risk of electrical hazards and prevent damage to the device itself. It's important to avoid using the appliance until it has been inspected and repaired by a licensed professional to ensure that it’s safe to use.

240V is the standard for more demanding appliances in the United States, whereas 220V is more common elsewhere. The voltage isn’t very different in any practical sense. The United States is a newer country compared to many other regions in the world with a faster adoption of new electrical needs. Appliances in the United States are often bigger than other parts of the world.