What would cause the lights to dim at our house when someone turns on/off an appliance?

I noticed recently that when someone turns on an appliance (like the microwave) at our house, the lights dim. It started recently but I haven't made any electrical changes at our house recently. What would cause that to happen?|||When a high current device turns on it will momentarily dim other things on that circuit. It is connected to the main lines at the circuit box so usually you don't notice it on other circuits. However it is is a heavy enough load, like the air conditioner it could dim lights throughout the house. Normally nothing to worry about unless it is excessive then you need to check connections.|||Call a qualified professional electrician to do a service on the panel. I suspect that one or more of the connections is loose or slightly oxidized and when the appliance is energized, the increased resistance of the dirty circuit causes the lights to dim because the IR drop has increased in the main panel. The IR drop across the connections should be zero, but dirt makes it increase.|||It means that the circuit isn't able to supply as much current as the appliances and light bulbs want. I'm not sure what would cause that to change over time, unless the appliance is drawing more power than before as a result of old age, or if there's a problem with a transformer outside your house. Or maybe you're using more light bulbs than before, with higher wattages?|||too small a main fuse or wiring , the initial load of appliances with motors is very high, much higher than the running current, if the wire cannot pass that much current at one time it heats up and reduces the voltage available to the rest of the house for a moment|||the electric supply for the lights is being over loaded. try turning off all appliances in the room then turn on the lights. If they dont dim, look at the electric braker that controls that room like a 20 amp, and check the total amprage you have pluged in.d|||a relocation of power or small power surge... nothing to be concerned just something that happens over time.