The LAW actually says nowt about auxiliary lights used on motorcycles.
That'll be because as far as the Road Vehicle (Lighting) Regulations 1989 (as amended) are concerned, there's no such thing as an "Auxiliary Light", be it on a motorcycle, car or whatever!
What it does say is this:
"Optional lamps, reflectors, rear markings and devices
Regulation 20: Every optional lamp, reflector, rear marking or device fitted to a vehicle, being of a type (type of lamp that is - Yeoman) specified in an item in column 2 of the Table below, shall comply with the provisions shown in column 3 of that Table."
Note that it says VEHICLE, which of course includes a motorcycle!
Now the schedules and provisions are long, complex and VERY BORING,
but as I said before, If it's a Fog Lamp, it must be used as a fog lamp and comply with the requirements for fog lamps. If it's a Driving Lamp (or to call it correctly, "a Main Beam Headlamp"), it must be used as a driving lamp and comply with the requirements for those.
It doesn't matter what sort of vehicle the lamp is fitted to. If it's fitted, it must comply with the reg's for that type of lamp.
So, my advice above still stands, use fogs as fogs and driving lights as driving lights.
Interestingly, I was a bit wrong when I said we could have any number of "Optional Front Position Lamps".
The regulations say this: (Schedule II, Part II)
REQUIREMENTS RELATING TO OPTIONAL FRONT POSITION LAMPS
1. In the case of a
solo motor bicycle first used on or after 1st April 1991 which is not fitted with any obligatory front position lamp, not more than two may be fitted which must comply with the requirement specified in paragraph 7 of Part I. Where two are fitted these shall be situated as close together as possible.
2. In the case of a
solo motor bicycle first used on or after 1st April 1991 which is fitted with one obligatory front position lamp, not more than one additional lamp may be fitted which must comply with the requirement specified in paragraph 7 of Part I and shall be situated as close as possible to the obligatory front position lamp.
So, it would seem that (assuming your GS is made after 1st April 1991) going by the Law, you can only have ONE optional additional front position lamp, right next to your existing position lamp, which, for our purposes, is about as much use as a chocolate teapot.
However, The good old European Union has implemented, or is in the process of implementing, a "Directive" which will require all powered vehicles produced from 2011 onwards, to have "Daytime Running Lamps" (DRL). I don't know too much about them yet, but hopefully when the Directive is absorbed into the Lighting Reg's, they will allow for a matched pair on motorcycles. That said, they may just make the manufacturers wire the motorcycle's dipped beam up so it's on all the time - assuming that's not already the case?
Like I said, if you want to run round with fog lamps or driving lamps lit other than in accordance with the Reg's, then you pays yer money and takes yer chance.
On my own setup, I'm using twinned Hella FF50 driving lamps, switched with the main beam and set to light the road up well ahead like they should. These are coupled with a pair of Ring "Illuminators" (which are actually fog lamps) and those are set to come on permanently with the dipped beam. That said, I've swapped the 55 watt bulbs for 35 watt bulbs, to reduce the drain on the battery a bit and have set them carefully, so they don't dazzle oncoming vehicles or melt the bloke in front's rear view mirrors. Not strictly in compliance with the Reg's, but that's the chance I'm prepared to take to make myself that little bit more visible.
Stay safe!
