|The MGA With An Attitude
FOG LIGHT and DRIVING LIGHT Applications - ET-205A
At 04:09 AM 10/16/2006 -0600, John Higginbotham in the UK wrote:
"Looking at your site I notice the fog lights FT6 and FT14 and seemingly a pair. Can you confirm this is the case? I have a pair of fogs for my mini that are marked FT9 and FT14 and I wasn't sure if they are actually a pair, or a mismatch."
Hang onto your seat. This could get long.
There is a wide variety of such lamps for fog light, driving light, LHD and RHD versions as well as different lens and reflector patterns. Many of them may look similar and may come in exactly the same metal housing. Unfortunately I don't have a Lucas lighting catalog, so I don't have a handy list of model numbers and descriptions. But I may be of some help anyway.
"Light" is generically the photo illumination which allows you to see things. "Lamp" is a nice term for the physical bulb or assembly of bulb and housing which will produce light. In slightly broader real world conversation, "lamp" may be a British word and "light" may be an American word referring to the same physical part(s) and (usually) not referring to the photo illumination. So we yanks refer to a "headlight" while the Brits refer to the same device as a "headlamp". The Brits commonly refer to windows as "lights", such as front light, back light, and side lights, which is why the term "lamp" makes more sense for a light producing device to avoid confusion.
The words "fog lamp", "spot lamp", and "driving lamp" may often be used in a generic sense when referring to any lamp mounted on the front of a car, which is totally confusing and misleading. If you see an ad saying "FT6 Fog/Spot lamp", the seller is confused and has no idea what he is selling. These words (should) have very different meaning referring to very specific features.
A "fog lamp" by definition throws a wide broadcast light output (flood light) which is intended to light a wide patch of road close to the car. These lamps should be mounted fairly low on the front of the car and be pointed slightly downward so they light the road full width close at hand and produce minimal reflected glare in fog. A fog lamp may be mounted below the front bumper for best effect (although may be mounted above the bumper as well). Lenses may be clear or amber and are usually fluted to break up the beam in random directions to reduce reflected glare. Some countries require a rear mounted fog lamp to be used to accent your visibility for a driver following your car in dense fog, in which case the lens may be red. Use of a clear lens in a front fog lamp is generally legal and common in older classic cars, but the clear lens can lead to identity confusion with other types of lamps.
A "spot lamp" by definition throws a near pencil beam of light to produce bright illumination on a very small area. These are commonly used in hand held lamps or a lamp mounted on the side of the windscreen which can be manually directed in any direction (to find a house number in the dark for instance).
A "driving lamp" has a slightly broader definition, most often referring to auxiliary headlights. Casual reference to any auxiliary front lamp as a driving lamp is erroneous. A fog lamp is definitely not a driving lamp. A "driving lamp" is used to see farther down the road in non-foggy conditions.
The most common form of driving lamp is the standard equipment headlights. These throw light generally forward and just a little to the sides to illuminate the road surface farther forward and across the width of one traffic lane (or a bid wider). They have a flat beam so as not to waste light on the road surface close to the car, and not to shine upward into the eyes of oncoming drivers. They are common in LHD and RHD versions where there may be a sharp cutoff of upward light on the side toward oncoming traffic, and the dip beam may be directed slightly to one side away from oncoming traffic.
An auxiliary "driving lamp" may be large or small, round or rectangular, and may have almost any mounting configuration (usually not below the bumper). They should almost always have a clear (not colored) lens, although there can be a wide variety of fluting or plain glass or a combination of flutes and plain glass it a single lamp. Driving lamps commonly have a light throw pattern similar to headlights, although the aux lamps may be more concentrated in the forward direction for better illumination farther down the road and less to the sides. Driving lights like headlights are usually mounted above the bumper to be aimed straight forward with the top of the beam perfectly level for long distance illumination. In most government jurisdictions it is required by law that driving lamps be wired to or triggered by the headlight high beam circuit, so than when you dip your headlights for an oncoming driver the driving lights will go out. This provision of the law is often not enforced, as the cops are usually happy if you just have at least two headlights that actually work.
Another form of "driving light" is physically similar to the description in the prior paragraph, but can have a spotlight type pencil beam intended to shine only straight forward for the longest possible distance. This type of driving lamp is commonly called "spotlight". These often have higher light output and are usually illegal for use on public roadways. They are commonly wired to a separate switch to be used only off-road. They may be mounted above the bumper, or on the bonnet, or above the windscreen or on the roof or on a roll bar. The location is a matter of personal taste chosen for best illumination depending on the intended use. Law will commonly require these lamps to be physically covered when the car is driven on a public roadway, even when the lamp is not switched on. If you have these lamps mounted above the front bumper and not switched on, who's to notice, and you may be okay without covers. But God forbid any cop should ever catch you with these lamps switched on when on a public roadway, which could result in severe penalties (plural) including impounding of the vehicle.
Now with the descriptions clearly understood, it is easy to tell the difference between a fog light and a driving light. Apply power and shine the light on a wall. A fog lamp will illuminate a wide area including somewhat off to the sides and may appear to be not terribly bright, as the light is widely dispersed. A driving lamp will have a light pattern similar to the common headlights, mostly forward, flat on top, not much to the bottom, and may (or may not) be distinctly asymmetrical for RHD or LHD. Single beam driving lamps are less likely to be asymmetrical. A spotlamp will have a pencil beam which will illuminate an area on the wall not much larger than the lamp itself.
For practical application you need to chose the lamp type to match the intended use. Lamps to be used in pairs should almost always be the same model number. However, it is (or was) fairly common for a classic car (back in the day) to have one aux fog lamp and one aux driving lamp wired independently to be used one at a time. If you use one fog lamp and one driving lamp it is most common to mount the driving lamp on the side nearest center of road for best long distance illumination, and mount the fog lamp on the other side nearest the side of the road to illuiminate the edge and shoulder.of the road. The Lucas 700 seven inch "Flamethrower" spotlamp was commonly used as a single driving light for racing or for official rally use when a roadway might be closed to public access. All jolly neat toys.
Getting back to your original question, .... I don't know the difference between FT6 and FT14 without a catalog in hand. They are both in the same housing, so hard to tell the difference by external appearance only. I think one is a fog light and the other is a driving light. The light output pattern is most affected and directed by configuration of the rear reflector surface. Either lamp could have a variety of glass patterns in the front lens. Each minor variation of lamp will have a different catalog number, so there are lots of different numbers within the general model designation. You can change from one model to the other by changing the globe (which is the outer glass shell with reflector and lens). As such the full catalog number may not be marked on the housing, as the same housing is used for different lamps. To know the exact model number you need a Lucas Lighting Catalog and you need to be able to identify the type of reflector and front lens and bulb.
By now you probably have less idea of the model of lamps in hand than before I started ramble. Trying to buy lamps on eBay is a black art, as most sellers will not provide the complete catalog number, and in most cases may not even know what they have. I don't have a Lucas Lighting catalog because I have never bothered with any aux lighting on my MG. I did once illegally mount spot lamps below the bumper on my old daily driver RX7 (to very good effect considering the intention), but that's a different long story.