At night, your eyes adjust to low light by dilating your pupils — but a sudden bright light, like oncoming high beams, can overwhelm that adjustment and leave you seeing poorly for a few seconds afterwards. Defensive drivers deal with this by shifting their gaze slightly toward the left edge of their own lane when an oncoming vehicle's lights are glaring, rather than staring directly at the approaching headlights, which helps preserve enough vision to stay in lane. It's also worth remembering that pedestrians and cyclists are far harder to see at night, so reducing speed and increasing following distance after dark gives you more time to react to hazards you may only notice at the last moment.
Source: Arrive Alive Road Safety Initiative
Frequently Asked Questions
Why do oncoming headlights affect my vision so much?
Your eyes adapt to low-light conditions by dilating, and a sudden bright light overwhelms that adaptation temporarily, reducing your ability to see clearly for a few seconds.
Where should I look when a car with bright lights approaches?
Shift your gaze slightly toward the left edge of your own lane rather than looking directly at the oncoming lights, to help maintain your lane position without being blinded.
Should I drive slower at night even on a familiar road?
Yes — reduced visibility means hazards like pedestrians, animals or stationary vehicles are harder to spot in time, so a lower speed gives you more reaction room.
Do clean headlights and windscreens make a real difference at night?
Yes — dirty or hazy headlights and windscreens scatter light and reduce clarity, which can meaningfully worsen glare and reduce how far you can see.