Final answer:
You should generally dim your headlights when an oncoming vehicle is within 500 to 1,000 feet and within 200 to 300 feet for following traffic. The closest answer from the options provided would be 200 feet for following traffic.
Step-by-step explanation:
The question regarding within how many feet should you dim your headlights when there is oncoming and following traffic doesn't correlate to the provided reference calculations concerning visual acuity, pupil diameter, and light diffraction. However, I can provide general guidance on this matter, but you should always consult your local traffic regulations as these rules can vary by jurisdiction.
Typically, it's recommended to dim your headlights when an oncoming vehicle is within 500 to 1,000 feet. For following traffic, the typical distance is to dim your headlights within 200 to 300 feet of the vehicle ahead. As none of the options provided (100, 200, 300, 400 feet) match the standard advice exactly, the closest correct answer, usually suggested for following traffic, would be (2) 200 feet.
It’s important to dim headlights to avoid blinding other drivers, which could potentially lead to dangerous driving situations.