Fog Driving Eye Strain: Dhund, Fog Lights and the Road Edge
In thick fog, full beam bounces light back into your eyes, so dipped headlights and a slower speed help more than squinting. Dhund, the winter fog of the plains, makes lane lines and road edges fade into grey, and your eyes work hard to find them even at low speed.
The short version
- Beam: Dipped headlights. Full beam reflects off the fog and makes a white wall ahead of you.
- Front fog lights: Only when visibility is seriously reduced, and switched off once it lifts.
- Rear fog light: Only in seriously reduced visibility, because it can dazzle other road users and obscure your brake lights.
- Guide: The road edge, not the tail lights of the car ahead.
- Rule of thumb: In fog, slow down before your eyes tire, not after.
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Why do your eyes ache in dhund even at low speed?
In fog the road has very little contrast, so there is less for the eye to grab. Your eyes keep refocusing and squinting to pick out a kerb, a lane mark or the edge of the tarmac. That effort can leave the eyes and forehead aching after a long foggy drive. The problem is seeing, and a slow car in thick fog still asks a lot of your eyes.
The Met Office warns that fog can give the illusion of moving in slow motion, so keep an eye on your speed. The lights of the car in front make the job look easier than it is, and they can give a false sense of security.
Which lights should you use in dense fog, and in what order?
- Dipped headlights first. The UK Highway Code says headlights must be used when visibility is seriously reduced, generally when you cannot see more than 100 metres.
- Front fog lights next, only when visibility is seriously reduced. Use them for the extra light the fog needs, not as a permanent setting.
- Rear fog light only in seriously reduced visibility. It can dazzle other road users and obscure your brake lights, so switch it off once the fog thins.
- Never use full beam. The Met Office says full beam reflects off the fog, causing a white wall effect that cuts what you can see.
- Switch fog lights off as soon as visibility improves. Leaving them on dazzles other road users.
The common thread is simple: use fog lights when the fog is thick, not all the time.
Should you follow the car in front or the road edge?
Follow the road edge wherever you can see it: the kerb, the verge or a line of reflective posts. Keep your eyes a little further ahead than the car in front, rather than fixed on its tail lights. Leave a bigger gap than usual, because in fog you see the road ahead later than you normally would.
The white wall check
Switch from full beam to dipped headlights, then look at the fog ahead. If the fog glows white and the road edge is harder to see than before, you are using the wrong light, going too fast for the fog, or both. Slow down, then keep the car on the road edge rather than on the lights in front.
Are yellow tinted glasses worth buying for fog?
Not on the evidence available. A 2019 study of 22 people in JAMA Ophthalmology, tested in a driving simulator at night, found that yellow-lens night-driving glasses did not improve pedestrian detection. The AAO summary describes night glare and pedestrians, not fog. The AAO summary of it says yellow lenses may improve comfort but do not change how well drivers detect things. Any tint also cuts some light, and fog already cuts a lot of it.
How do you keep your eyes fresher on a foggy drive?
Start with a clean screen, inside and out. Use the demister and the wipers, and wipe the inside of the glass with a microfibre cloth, since a smeared film catches headlight glare. On a long drive in fog, pull off somewhere safe when you can, and rest your eyes for a few minutes, looking at something far away rather than at a screen. Avoid staring at one spot on the road. Let your eyes move between the road edge and the lane mark ahead.
Which habits should you swap when the fog comes in?
Most fog strain comes from a few habits that are easy to change. The table lists the swaps.
| Instead of | Try |
|---|---|
| Full beam in fog | Dipped headlights |
| Fixing on the tail lights ahead | The road edge, with a bigger gap |
| Fog lights on all the time | Fog lights only when visibility is seriously reduced |
| A smeared inside screen | Clean inside and out with a microfibre cloth |
| Yellow glasses as a fog fix | Slower speed and a clean screen |
If the fog is too thick to follow the road edge, pull off the road somewhere safe when you can, and wait for it to lift. Do not push on through a white wall because the trip feels urgent. If your eyes still ache after the drive, your sight stays blurred, or you have eye pain or a headache, see an eye doctor or your GP. An optician should also check your glasses if fog and night driving keep feeling harder than they should, because a prescription that is slightly off can make low-contrast driving harder.
Fog driving and tired eyes: the questions drivers ask
How do I drive safely in fog?
Use dipped headlights, slow down, keep a bigger gap than usual, and follow the road edge rather than the tail lights of the car ahead. Turn fog lights off once the fog lifts.
Should I use fog lights or headlights in dense fog?
Use dipped headlights first, and add front fog lights when visibility is seriously reduced, generally when you cannot see more than 100 metres. Do not run fog lights all the time.
When should I use the rear fog light?
Only when visibility is seriously reduced, because it can dazzle other road users and obscure your brake lights. Switch it off as soon as the fog thins.
Is high beam bad in fog?
Yes. Full beam reflects off the fog and makes a white wall that cuts how far you can see. Use dipped headlights instead.
Are yellow glasses good for fog driving?
There is no good evidence that they help. A 2019 study found that yellow lenses did not improve night-time pedestrian detection, and that study describes night glare, not fog, so do not buy them as a fog fix.
Why do my eyes hurt when driving in fog?
Fog lowers contrast, so your eyes keep squinting and refocusing to find the road edge. Dipped beams, a clean screen, slower speed and short breaks reduce that load. If the ache does not clear, see an eye doctor.
What if the lane lines disappear in fog?
Follow the road edge, which means the kerb, the verge or a line of reflective posts. Slow down, keep your eyes on the road ahead, and avoid fixing on the car in front.
How far can you see in dense fog?
It varies, and dense fog can cut your view well below 100 metres. The Highway Code marks seriously reduced visibility as generally when you cannot see more than 100 metres, which is the point to use fog lights.
Is it safe to drive in dhund early in the morning?
Only if you can see the road edge and the trip cannot wait. If the fog is too thick to follow the road edge, stop somewhere safe and wait for it to lift.
Should I clean the inside of the windscreen before a foggy drive?
Yes. A smeared film on the inside catches headlight glare, which makes fog worse. Use a microfibre cloth and the demister before you set off.
What is known and what is not about fog and eyes
The clearest guidance is about lights and speed: dipped beams, fog lights only when the fog is seriously thick, and a slower pace with a bigger gap. The evidence for coloured glasses is weak. For more on the eye side of winter, see Eye Care, and for the night side of glare, read night driving glare and halos. Dry eyes from heaters on the same drive are covered in dry eyes in winter, and a longer test for screen and glasses strain is in eye strain from screens and glasses.