Fog Lamps

Fog LightsMy article on driving lights led to a number of requests to write a follow up article on fog lights. The original question involved vehicles that were driving with four lights on all the time and two of them were not being dimmed for oncoming traffic. Many readers were aware that the extra two lights were fog lights and not driving lights.

What is a Fog Light?

Fog lamps are identified by the SAE F marking on the lens, or a B above the circle with the E in it on European lamps.

Fog Light ID Marks

Fog Light Installation

B.C.'s Motor Vehicle Act Regulations (MVAR) allows two fog lamps that emit either white or amber light. They must be mounted on the front of the vehicle, below the headlamps, but not more than 30 cm below. When you switch them on, the parking lamps, tail lamps, licence plate lamp and, if required, clearance lamps must also illuminate.

However, the Vehicle Inspection Manual used by Designated Inspection Facilities to insure vehicle equipment complies with standards also mentions red rear fog lights. Two are allowed and must be mounted no further than 10 cm. away from the brake lights.

The two sets of rules have been out of step for a long time.

When Should You Use Fog Lights?

According to vehicle lighting expert Dan Stern, you should "turn them off, leave them off and forget that they exist." Front fog lights are really only useful in a very narrow set of circumstances.

Despite this, the MVAR says that front fog lamps may be used in place of headlamps if atmospheric conditions make the use of headlamps disadvantageous.

Beyond that, front fog lamps may be used at any time of the day or night and in fact are used as the daytime running lamps on some vehicles.

The MVAR doesn't say anything about the use of rear fog lights. Dan suggests that a good metric to use in deciding when to switch your rear fog lights on or off is "Do I wish the guy in front of me was displaying a rear fog so I could see him better / Do I wish the jerk in front of me would turn off that damn bright red light?".

How to Aim Front Fog Lights

As with driving lamps, fog lamp aim is measured at a distance of 7.62 m from the lamp.

If the beam is symmetric, aim is measured at the center of the top edge of the high intensity area. They must be 100 mm below horizontal with an upper error of no more than horizontal. Lateral aim is straight ahead, but must be no more than 150 mm either side of vertical.

If the beam is asymmetric, aim is measured at the left of the top edge. They must be 60 mm above vertical with an error of no more than 175 mm above to 50 mm below horizontal. They must also be aimed straight ahead but must be no more than 100 mm either side of vertical.

front fog light aiming

Comments

No Fog? No Fog Lights.

There should be quite a big fine for the use of fog lights at any time except for when they are required for very foggy conditions. There should be an even bigger fine for improperly aimed fog lights that shine very brightly into the eyes of oncoming traffic. The use of fog lights when not required is a real hindrance to oncoming traffic In the past I have tried turning fog lights on when there is no fog and no traffic coming at me and I found that I would tend to be looking at the road very close to the front of the car as it is a lot brighter there instead of looking further up the road where we should be watching. Fog lights on my vehicles are rarely ever turned on unless it is so foggy that it is very hard to see the road.

Read Fog Lights

Back when I lived in the UK, rear fog lights were a royal pain in the eyes.  The regulations over there require all cars to be fitted with them.  Although they can be a lifesaver in fog, the problem is that the driver has to remember to switch them off.  It isn't unusual to see vehicles with them on literally months after the last fog!  If it is dark and raining it is awful driving behind them.

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