Final answer:
Headlights should be used during low visibility conditions, like at night or in bad weather, and when you cannot see 500 feet ahead. If automobile wires were superconductors, there would be no dimming due to wires when starting the engine, but the battery's resistance might still cause it.
Step-by-step explanation:
You must use your headlights whenever visibility is significantly reduced, typically during the night, in fog, rain, or any adverse weather conditions that make it difficult to see the road ahead. Besides using them when windshield wipers are on, headlights should also be used from sunset to sunrise, when approaching tunnels or during times when the weather conditions require drivers to enhance their visibility to others. Additionally, some states require headlights to be on if you cannot see a certain distance ahead (often around 500 feet).
Regarding the take-home experiment, waving your hand back and forth between your face and a fluorescent bulb, you might observe a flicker due to AC current. This flickering effect is generally not seen with car headlights as they are supplied with DC current, but you may observe a slight dimming when turning on the engine, as mentioned above due to the battery's internal resistance.
When discussing the scenario with the driver leaving the headlights on after parking the car, knowing the battery's capacity and the power rating of the headlights can help to estimate how long the headlights will last. A 12-V battery rated at 100 Ah providing power to two 12-V headlights, each at 40 W, can be expected to last for a certain number of hours based on the power consumption.