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Driving lights vs. Fog lights

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Cocoa, FL, USA   USA
I bought a light bar with two lights attached to it nice chrome round Lucas lights,looks great but I have to buy bulbs for them. I planned on wiring them in parallel but not sure whether to buy driving or fog bulbs. Mostly for looks anyway,I think the bulbs are interchangable. Greg.Any thoughts?

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warekl Avatar
warekl Silver Member Keith Ware
White Bear Lake Mn, USA   USA
1973 MG MGB GT
1979 MG MGB
The bulbs are only part of the difference between fog and driving. The light pattern is very much different. look at images of them and you will see different lens patterns and sometimes reflector differences too.

Determine what you have and go with those bulbs...

USMC ... Semper Fi
79 RB Lowered, HS4s by Dave Braun & "Schlemmerized" 25D Dizzy, 9.5:1 CR, Mild Performance Cam, 18V with OD Tranny.

73 GT in Black Tulip

greenrman Gold Member Don B
Kelowna, BC, Canada   CAN
1973 MG MGB "Oscar"
2005 BMW 3 Series Cabriolet "Sabrina"
(an aside....Greg, I've always wondered whether those grille bar fogs were a factory or dealer or aftermarket option. 5yr B'er,...learning as I go. Throwing this Q whilst here surfin)

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Rod H. Avatar
Amity, OR, USA   USA
1964 MG MGB
1968 MG MGB GT
I have driving lights on one MGB and fog lights on the other. You are probably right...mostly for looks. The H4 headlights on the one with driving lights are very bright on high beam, so the driving lights don't help much. The low beams swamp the pencil beam fogs on the other car.

One thing I can say positive about the fogs is that they give improved lighting low and to the sides for cornering or seeing ditches and other objects on dark nights. But I haven't driven the car at night in ages. Maybe you do though, so ones with a nice wide pencil beam may be helpful for you.

I can't understand why people are frightened of new ideas. I'm frightened of the old ones. John Cage

'63 MGB
'80 VW Vanagon Kombi
'09 Mazda 3 with 5 speed manual

Edited 1 time(s). Last edit at 2019-02-10 07:12 PM by Rod H..

tahoe36c Avatar
tahoe36c Paul Hruza
Panama City, FL, USA   USA
1969 MG MGC GT "Little Red Rocket..."
1972 MG MGB GT "Tiny Dancer"
2002 Harley-Davidson Dyna
Driving Lights = Really just an "extension" of High Beams used on clear night driving. Additional light in the distance. I had some Hella H4 driving lights on my BGT when I was in the UK back in the 80s.

Fog Lights = Meant to keep the light down low and to the side of the road (opposite oncoming traffic) since the light cannot penetrate fog. Upgraded low beams...

The bulbs themselves are usually not different. The focal lens is the difference... The manner in which the light is dispersed in front of the vehicle. Light is light is light... The only difference will be Lumens (previously known as Candlepower or Candlelight) and Color Temperature.

If you've ever driven home from swingshift on a densely foggy night from work (as I did in the UK) you would understand! My room mate had to drive his Mini as I held the passenger side door open to literally watch the side of the road in order to get home! Hence the fog lights focus on the side of the road...

Edited 1 time(s). Last edit at 2019-02-10 08:32 PM by tahoe36c.

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MG 010.jpg

Fairfield, CA, USA   USA
the effect is mostly cosmetic, unless you do a lot of nighttime driving in dark area, OR are into pro/semi-pro rally. Then the difference is substantial.

Otherwise, I wouldn't bother.

1973 Pale Primrose Roadster. A nice 10-footer!
SUs, Datsun 5-speed

tahoe36c Avatar
tahoe36c Paul Hruza
Panama City, FL, USA   USA
1969 MG MGC GT "Little Red Rocket..."
1972 MG MGB GT "Tiny Dancer"
2002 Harley-Davidson Dyna

I have to kindly disagree sir!!! There is a HUGE difference between fog/driving lights and normal headlights...

The fogs on my Honda Accord make a big difference for lighting low and the roadside at night. I use them even without fog to help see all the deer along the side of the road at night. Come take a ride with me and you'll see when I flip them on and off!!

And the Hella's could be used to spot deer with the MGB... They reached out quite a bit farther than the normal headlights (which were also H4 bulbs).

It's all about the focus of the lens.

allanreeling ALLAN R
The trouble with fog, apart from grossly reducing visibility, is that the water particles reflect the light back at you. Fog lights have a wide flat top beam and are more effective when mounted low down. Less light is thrown back at you. At one time the bulbs were often yellow, but whether that made any difference is debatable.


tvrgeek Avatar
tvrgeek Silver Member Scott S
Hillsborough, North Carolinia, USA   USA
1965 MG MGB
Yes, yellow does make a difference. Driving in the mountains in Colorado in blizzard conditions I can attest to it. Not magic, but it helps. Quality of the reflector and lens does as well. But, always a "but", US laws are really stupid in that you must have your low beams on with the fog lights eliminating the advantage of the low beam with less glare. I routinely ignore the law and run my fogs with running lights, but no low beam. It is also illegal in the US to run fogs with the high beams. That only kind of makes sense. Barely. To think about it, driving around in the city and our overly lit up suburbia, fog lights would work better for about half our night driving as they don't glare others eyes as much.

Driving lights are less important now that we have such high power main high beams unless you live in very rural areas where you can use them. Maybe in deer (or roo) country highways. Or a new Mini Cooper that must have the worst beam projection of any car built in the last 50 years.

Interesting. I passed a truck coming home the other night who had this massive, maybe 6 foot by 1 foot light bar on the front. Lit up the whole area, but as I passed, the glare was not bad. He did turn it off quickly, but not before I noticed.

While talking lights, I will rant on HID lights again. The higher spectrum, white to blue, is what causes the most glare. Maybe you can see a little better, but oncoming traffic is blinded longer. So you can see the blinded car run into you better. Headlights should be back to the lower temp ( as in color, referenced to hot black object) limited to maybe 2500 degrees. HID's are 4300 OEM to as much as 8000 in aftermarket. The older you get, the more sensitive to glare you are.

Cogito ergo sum periculoso

Rob-USLE Avatar
Rotterdam, ZH, Netherlands   NLD
On Lucas (and other brands) you simply can see the difference between FOG (width light bundle) or DRIVING (narrow light bundle) in the lens of the lamp.
The lights do use the same bulb, however there are are people who think yellow light is FOG and white light is DRIVING.

I'll explain it with same pictures of Lucas Square 8 lamps (few n.o.s.) which I owned and sold over the years.

For those who still don't believe it, on the box with the yellow fluted light you can still read FOG,
the pair of SPOT lights in the original boxes a p.o. of the set wrote "mistlamp" (fog lamp) on one of the boxes but they are DRIVING/SPOT lights as the box is marked ex factory.

So a total ( from left to right) fluted lens is FOG light and a lamp with just fluted in the middle lamp is DRIVING, dispite the color of the lens (or bulb), the lens gives the far away or width pattern.

Edited 1 time(s). Last edit at 2019-02-11 05:15 AM by Rob-USLE.

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allanreeling ALLAN R
Scott, Yes and the lower your car, e.g., MG, the worse is the burnout on your retina!!


Bill Morris Avatar
Nor Cal, USA   USA
1971 MG MGB
You can tell which type of lite (fog or spot) by the number of flutes in the lens. Fog lites have more flutes in the lens than the spot lite lens. I found them to be a major help when I lived in "snow country". I found that a spot on the drivers side and a yellow fog on the rite side (U.S.) worked well. The yellow allowed the driver to discern the difference between ice, snow or water on the road ahead.
Good find.

Blinded by the lite...

Home of the wayward cars...feel free to drop one off anytime.

ingoldsb Avatar
ingoldsb Silver Member Terry Ingoldsby
Calgary, AB, Canada   CAN
1971 MG MGB
Paul x2.

I wish I had the old Cibie sales literature - it clearly showed the difference in the beam patterns.

You might look at Daniel Stern's lighting website (Google using those terms). He provides a wealth of information.

Terry Ingoldsby

ls1ac Avatar
ls1ac scott sommer
bristol , Englewood, wi , Fl, USA   USA
There IS a very big difference in the aux lights. The fog should have a "table top" pattern. No light above the cutoff line. they should be mounted low and pointed just below horizontal. This minimizes the reflected and scattered light from coming back and making everything seem to white out.
Cibie was the default standard for years. Unless things have change in the very recent past there are only two company's that make SAE rated LED fog lights. The one I am familiar with is PIAA, they achieve the cut off line with a backward facing led and a mirror.
Driving lights usually are pencil or standard. As you can guess the pencil is very narrow with a long range and the standard covers the whole road.
The patterns are determined by the lens and the reflector.
Side note, the amber fog was thought to work better until the new bulb design with the smaller filament was introduced. Now most drivers prefer the white with the exception of driving in a snow storm where it is thought that the amber will highlight objects better in the white conditions.
New domestic cars with the "fog" lights are a joke. Some imported cars from Europe do have working fog lights, The funny thing there is when the drivers turn on the front fog it will also turn on a single bright red light in the back. It looks like a brake light is stuck on.
I believe the PIAA web page shows patterns

ohlord Avatar
ohlord Gold Member Rob C
North of Seattle, N.W., USA   USA
1957 Land Rover Series I "EYEYIYI"
1971 MG MGB
1971 MG MGB "Bedouin 2"
Install relays

"I'm a long way gone down this wild road I'm on
It's gonna take me where I'm bound
It's a long way around"

"These are the days that must happen to you"

RD2 Radar/ Electronic Warfare Technician
Vietnam 1969-1972

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