so assuming your using 10 gage wire with .0033 ohms/meter of resistance, and that the total circuit length is 2 light seconds long(599584916m). the circuit diagram would be as such with a 1MOhm resisters between the load and the current source on each end because the resistance of the wire far outweighs that of the load the voltage spike after 1 sec would in my understanding be minimized. This could be modeled as almost an open circuit at the 1MOhm resisters. assuming the light was designed to run at the voltage drop accost it in this scenario it would in fact light up almost instantly or 1/cs from the activation of the switch. I would need an actual test to prove this hypothesis but interesting thought experiment to say the least
