Fwd: AUDI 200 REAR FOG light

[isham-research.freeserve.co.uk at pop.pol.net.uk]

> Depending upon the wattage of the bulb you use, you may be overloading
> the wiring to the driver's side rear fog by splicing in the other
> socket to have two rear fogs. Be aware, the concept of having only one
> rear fog light (well explained in someone's, I unfortunately forgot
> whoms, sorry, post) is a safety issue:

Yes it is, and the post was probably mine.  Running with two fog lights
is illegal in many European countries.  In the UK, it depends on the
year of first registration - I think the legal requirement for a single
light on the offside of the car is from 1 September 1993, though I'm
not absolutely sure.

The reason is that twin rear fogs mask the 'startle reflex' effect
deliberately designed into brake lights.  Rear sides are 5w in the UK,
and brake lights 21w.  Taking reflector designs into account - side
(marker) lights have a wide spread, brake lights are focussed into more
of a beam - the perceived brightness difference is 1:64 at the eye.  The
eye is a remarkably accomodating organ, but this difference is enough to
'startle' it and cause a reaction - even if the change occurs in
peripheral vision.  If both sides have rear fogs, the ratio between
overall apparent luminance with and without the brake lights is reduced
to 1:2 or 1:4 - not enough to generate a startle reflex in peripheral
vision.

Yes, you'll see the brake lights come on if you're looking directly
at the back of the car.  But if you just happen to glance away at the
instruments you're dependent on that startle reflex.

Also the law in the UK allows their use only when visibility is less
than 50 metres and specifically forbids their use in rain.

--
 Phil Payne
 UK Audi quattro Owners Club
 Phone +44 7785 302803   Fax: +44 7785 309674