Vehicle Fog Lights - Best?
Bill
newer fog lights that are round shaped and seem to be higher in
intensity. Also there are older rectangular design lights that are
white.
Which is the best to see in fog? Should it have a yellow lens?
Frank Wood
Bill wrote in message ...
>For years vehicle fog lights seemed to all be yellow. Now there are
>newer fog lights that are round shaped and seem to be higher in
>intensity. Also there are older rectangular design lights that are
>white.
The shape of the lamp isn't really relevant. It's all in the lens. The beam
from a fog light should be wide and shallow. better than 90 degrees wide,
and maybe only 1 degree high. I had a wonderful pair once, made by Carello.
The idea is that you can see the sides of the road, or the markings.
>Which is the best to see in fog? Should it have a yellow lens?
There is a theory that yellow light is less reflected by fog. I've never
seen any evidence for this. The only reason a 55W yellow lens lamp gives you
less kickback from the fog than a 55W white lens lamp is that half the
output has been absorbed by the filter!
France used to require yellow headlights on vehicles registered in that
country. Since they changed that rule, it's better than a even chance that a
car with yellow headlights is being driven by some fool of an Englishman,
who believes that painting yellow lacquer on his headlights converts them
from RHD to LHD. It doesn't!
Daniel Stern Lighting
> The shape of the lamp isn't really relevant.
For a given size, round lamps are more efficient than rectangular lamps,
since rectangular lamps' sides, top and bottom cannot be used to collect
and project light.
> from a fog light should be wide and shallow. better than 90 degrees wide,
Wide, yes. "Shallow", no. The two main characteristics for a fog lamp
beam are width (wider = better) and a sharp horizontal cutoff at the top
of the beam, with minimal-to-zero light above the cutoff.
> and maybe only 1 degree high.
One of the main functions of a fog lamp is to provide strong forefield
illumination so that in worst-case conditions when you cannot see through
the fog, you can see where the road is. A shallow beam doesn't get this
job done.
> I had a wonderful pair once, made by Carello.
Carello used to make some very good fog lamps.
The Italians are even worse marketeers than the French, as it seems,
though.
> There is a theory that yellow light is less reflected by fog.
That is true to some degree, in some kinds of fog, and with a very
specific color of yellow called "selective yellow". There is a VERY narrow
IEC definition of selective yellow.
Selective yellow light is obtained when you subtract blue from an auto
headlamp: Blue is the shortest wavelength and, as such, scatters the most
readily. (To prove this to yourself, find a dark blue store front sign or
something else that's a dark, pure blue against a dark background in the
absence of white light. From any appreciable distance, it's almost
impossible for your eyes to see the blue lighted object as a sharply
defined form...the edges blur significantly.)
When blue light strikes water (rain, fog, snow) it scatters in all
directions and makes on-road vision very difficult.
Blue also is a very difficult color of light to look at if it is at all
intense...it stimulates the reaction we call "glare".
So the French figured to remove the blue from the output spectrum of their
vehicles' front lamps. White light with the blue component subtracted is
known as "selective yellow" light. It is a pure yellow color with little
or no orange component--hence the French yellow headlamps. There haven't
been any recent comparative studies. Yellow lamps were subjectively ranked
as better in poor weather and lower in glare than white ones, and this
matches my own experimental experience with fog lamps that produce yellow
light. But is the effect real or just an illusion?
One problem with this conclusion as drawn from the French experience with
selective-yellow headlamps in France is that when the question was being
considered, the lamps that were being compared with white lamps reduced
the absolute intensity of the beam by about 12 percent (average). This
fact may have had a part in reducing the glare. Because the requirement
for yellow light no longer exists (though such light is optional in many
countries) we probably will never know the vagaries of the answer to this
question.
A good fog lamp has almost no upward light and a very sharp cutoff. (And a
well-placed fog lamp is mounted low to the ground, to maximize vertical
separation between the driver's eyes and the cutoff of the beam pattern,
thus throwing light "under" the fog blanket from the driver's
perspective.) Now, selective-yellow light is, subjectively, a better color
for a fog lamp because the main part of the beam (below the cutoff)
creates the effect of less-glaring backdazzle. The only condition under
which selective-yellow light (or any kind of yellow light, for that
matter) has actual, physically greater penetration power is in what is
called "blue fog", in which the water droplets are many, many times
smaller than the droplet size found in common atmospheric fog. A fog lamp
is not defined as "yellow", but as a lamp that produces a very wide bar of
light with minimal-to-no uplight and a sharp horizontal cutoff, and the
determinant of a good fog lamp is amount of uplight (less is better) and
sharpness of cutoff (sharper is better), not beam color. Selective-yellow
light can improve fog lamp performance, because it is lacking in the high
frequency/short wavelength blue light that reflects readily off
atmospheric moisture (frozen or not) and into your eyes. I prefer
selective-yellow fog lamps, though I would certainly take a good white fog
lamp over a poor selective-yellow one. (My preference is for good
selective-yellow ones!).
Modern methods of obtaining selective-yellow light, such as the placement
of a yellow-pass dichroic filter on the bulb envelope, on the reflector or
on the lens, can create more problems than they solve. The blue-appearing
lenses in many Asian-made fog lamps ("ion crystal", "gold irridium", and
other nonsensical marketing names) are coated with a multilayer dichroic
interference coating which passes selective-yellow light "on axis", which
means "straight ahead". Unfortunately, these coatings tend to glow blue
when viewed off-axis, which has caused problems with people getting pulled
over for illegal "blue" lights 'cause the cop sees blue.
Many lamps involving dichroic filter coatings on the bulb, reflector or
lens tend to create "blue haze" above the beam cutoff or, in the case of a
driving or SAE headlamp beam, scattered throughout the beam. That's
because of the irridescence of these coatings, which causes or aggravates
secondary-reflection problems where none would exist absent the coating.
With the mirrorlike dichroic coating reflecting images of the glowing
filament, light gets where it doesn't belong. None of these effects help
the performance of your lamps at all! Headlamps should be white, and it is
best to stick with regular, clear bulbs! Blue light is NEVER used in
performance halogen lighting, ONLY in poseur items.
> I've never seen any evidence for this. The only reason a 55W yellow
> lens lamp gives you less kickback from the fog than a 55W white lens
> lamp is that half the output has been absorbed by the filter!
Erm, no. The LEAST-efficient selective-yellow filters subtract around 18
percent of the source light...nowhere near your "half" guess. The most
efficient ones remove less than that, and the benefits of selective-yellow
light in poor weather mean that this color can be a better choice than
white. It's not a deciding factor; I'd certainly have a good white fog
lamp before I'd have a poor selective-yellow one, but I'd prefer to have a
good selective yellow one.
> France used to require yellow headlights on vehicles registered in that
> country.
There's no reason to have selective-yellow headlamps unless you're driving
in REALLY foul conditions and need to do everything in your power to
minimize backscatter. The reason France required selective-yellow light
from all forward-facing vehicle illumination lamps was originally that
when France was invaded, it was necessary to be able to identify the
nationality of a car at night, but without reducing roadway safety. The
technical papers on the adoption of selective-yellow light are quite
interesting to read. The physiology of the direct-glare reduction from SY
light is valid (for a given intensity, SY light is less glaring than
white), and the backdazzle reduction is likewise real for certain bad
weather conditions. France kept the rule LONG after the original
nationality-identification need was quite obsolete.
As for the original poster's question about older versus newer fog lamp
designs, caution is warranted. There is more garbage on the
auxiliary-lamp market than ever before, and a lot of phony pseudotechnical
mumbojumbo being used to sell it. Most of the miniature eyeball- or
flat-oval shaped items come from a couple junk factories in China, boxed
and packaged in any of many marketing companies' livery. Of the
newer-styled designs, Hella's Comet FF 100/200/300 and Micro DE series are
some of the best. Among longtime-successful designs, the Cibie lineup and
what's left of the Marchal line are still top-notch. Bosch makes some
acceptable stuff and some junk, and Hella has waded into the junk market
'cause there's a lot of $$ to be made there. Best rule is never to assume
based on brand name or on a glossy brochure, but to ask a specialist
(myself or another) for advice and assistance.
--Daniel
TO WRITE TO ME: Remove the headlamp from my return address.
.______DANIEL STERN LIGHTING______.
| http://lighting.mbz.org |
---
dastern "at" vrx "dot" net
Automotive Lighting and Signalling Services
NBCS b6f+wg++rp
Terry McGowan
Daniel Stern Lighting <das...@vrx.headlamp.net> wrote in message
news:Pine.SOL.4.02.100013...@azure.engin.umich.edu...
> Selective yellow light is obtained when you subtract blue from an auto
> headlamp: Blue is the shortest wavelength and, as such, scatters the most
> readily. (To prove this to yourself, find a dark blue store front sign or
> something else that's a dark, pure blue against a dark background in the
> absence of white light. From any appreciable distance, it's almost
> impossible for your eyes to see the blue lighted object as a sharply
> defined form...the edges blur significantly.)
Some will remember "blue dot" brake lights on customized cars that
illustrate the effect as well -- a few still seem to be around. They
consist of a standard red tail light lens with a small blue refractor lens
in the middle. Close up, you see what looks like a normal red tail light.
From a distance when the brakes are applied, the blue light scatters and
overwhelms the red.
Terry McGowan
JCWCONSULT
One other item bears mentioning.
IF we had ECE headlamps, with their far superior flat cutoff on low beams,
99.9% of what passes for optional fog lamps from auto makers would be shown to
be pretty worthless. Good ECE headlamps outperform virtually all optional
equipment fog lamps fitted by vehicle makers and only by going to some of the
best ones that Daniel mentions could you get any real gain.
Alas, NHTSA prohibits makers from fitting the best ECE headlamps which give
both better light than almost all SAE lamps AND quite good fog performance as
an extra benefit.
Regards,
Jim Walker
Douglas G. Cummins
>
> On Sun, 30 Jan 2000, Frank Wood wrote:
>
> > from a fog light should be wide and shallow. better than 90 degrees wide,
>
> Wide, yes. "Shallow", no. The two main characteristics for a fog lamp
> beam are width (wider = better) and a sharp horizontal cutoff at the top
> of the beam, with minimal-to-zero light above the cutoff.
>
> > and maybe only 1 degree high.
>
> One of the main functions of a fog lamp is to provide strong forefield
> illumination so that in worst-case conditions when you cannot see through
> the fog, you can see where the road is. A shallow beam doesn't get this
> job done.
Daniel, I agree with everything you have said here but wanted to
clarify a point - the beam height should be narrow/shallow enough to
prevent reflected glare from water and ice on the road. A beam height
of 3 to 4 degrees with the maximum intensity around 2 degrees below
the horizontal is common and starts illuminating around 15 to 20 feet
in front of the vehicle (depending on how high the fog lamps are
mounted).
Douglas Cummins
Calcoast - ITL
Frank Wood
Daniel Stern Lighting wrote in message ...
>
>There's no reason to have selective-yellow headlamps unless you're driving
>in REALLY foul conditions and need to do everything in your power to
>minimize backscatter. The reason France required selective-yellow light
>from all forward-facing vehicle illumination lamps was originally that
>when France was invaded, it was necessary to be able to identify the
>nationality of a car at night, but without reducing roadway safety.
I'ld like to see the evidence for this.
As for "selective yellow", which I take to be an accurately defined colour,
French headlamps used to be 77 different shades, according to manufacturer's
whims. Plus the Brits' painted headlamps!
Frank Wood
fr...@woodf-l.dircon.co.uk
Daniel Stern Lighting
> >The reason France required selective-yellow light
> >from all forward-facing vehicle illumination lamps was originally that
> >when France was invaded, it was necessary to be able to identify the
> >nationality of a car at night, but without reducing roadway safety.
>
> I'ld like to see the evidence for this.
Contact Guy D'orleans at Valeo in France.
> As for "selective yellow", which I take to be an accurately defined colour,
> French headlamps used to be 77 different shades, according to manufacturer's
> whims.
Well, there're also many different shades of "white" headlamp light, from
the brownish-white of a tungsten sealed beam to the purple of some HID
headlamps.
Daniel Stern Lighting
> > > and maybe only 1 degree high.
> >
> > One of the main functions of a fog lamp is to provide strong forefield
> > illumination so that in worst-case conditions when you cannot see through
> > the fog, you can see where the road is. A shallow beam doesn't get this
> > job done.
>
> Daniel, I agree with everything you have said here but wanted to
> clarify a point - the beam height should be narrow/shallow enough to
> prevent reflected glare from water and ice on the road. A beam height
> of 3 to 4 degrees with the maximum intensity around 2 degrees below
> the horizontal is common and starts illuminating around 15 to 20 feet
> in front of the vehicle (depending on how high the fog lamps are
> mounted).
Good point, good clarification.
Stephen H. Westin
<snip>
> France kept the rule LONG after the original
> nationality-identification need was quite obsolete.
Come, now: in France, the need to identify nationality will *never* be
obsolete :).
<snip>
--
-Stephen H. Westin
Any information or opinions in this message are mine: they do not
represent the position of Cornell University or any of its sponsors.
Daniel Stern Lighting
> > France kept the rule LONG after the original
> > nationality-identification need was quite obsolete.
>
> Come, now: in France, the need to identify nationality will *never* be
> obsolete :).
BOLSCOM!!
DS
Frank Wood
Daniel Stern Lighting wrote in message ...
>
>the brownish-white of a tungsten sealed beam to the purple of some HID
>headlamps.
>
a randomly applied coating of dirt, dust or mud, which can also affect the
beam pattern by applying a diffusing coating to the lens. That apart, unless
you insert a filter of some sort in the light path, the colour is dependant
on the filament temperature or the discharge characteristic, and hopefully
on nothing else. Since French headlamp yellows were wildly variable, and
always due to a filter of some sort, I don't think it can have been
accurately specified, as "selective yellow" or as anything else. That was
the point I intended to make.
Frank Wood
fr...@woodf-l.dircon.co.uk
Daniel Stern Lighting
> >Well, there're also many different shades of "white" headlamp light, from
> >the brownish-white of a tungsten sealed beam to the purple of some HID
> >headlamps.
> >
> Visibly true, although I think your 'brownish-white' is almost always due to
> a randomly applied coating of dirt, dust or mud
Evidently you've never seen a (perfectly spotlessly clean) tungsten sealed
beam headlamp in operation.
> beam pattern by applying a diffusing coating to the lens. That apart, unless
> you insert a filter of some sort in the light path, the colour is dependant
> on the filament temperature or the discharge characteristic, and hopefully
> on nothing else.
It's also dependent upon the type of optic in use, and upon the presence
and degree of the diffraction effects at the edges of the beam. (These
are the diffraction effects you stated some months ago you don't believe
in, despite much research into their control by major lamp makers).
> Since French headlamp yellows were wildly variable, and
> always due to a filter of some sort, I don't think it can have been
> accurately specified, as "selective yellow" or as anything else.
You may think what you like. The fact is, they were.
The normal human eye is very good at discerning color differences. French
headlamps were Selective Yellow, and the variances you saw indicate the
fact that the IEC defines colors as ranges, not as discrete spectral
lines.
Frank Wood
Daniel Stern Lighting wrote in message ...
>
sealed
>> >beam headlamp in operation.
Mea culpa! I missed the 'sealed beam'. They were better than what came
before, but we haven't had these around for more years than I care to
remember! The early sixties, probably.
>
(And you're still using
>dim tungsten sealed-beam headlamps on a daily
>driver...because...um...why?)
Obviously, I'm not!
>Aside from the fact that they were legally required to, and that
>compliance with this requirement was carefully checked on EVERY headlamp
>design, and aside from the fact that there was really not much variance in
>the color of headlamps when I was in France in 1990, 1993 and 1995...I
>have numerous French-spec headlamps in my possession, which use all
>different kinds of bulbs and all different methods of creating selective
>yellow light, and the color does not vary much from lamp to lamp.
I have to say that individual Frenchmen are largely indifferent to
regulations. Their yellow lights were produced in two basic ways, with
yellow lenses, and with yellow bulbs. What happens when you mix the two? I
spend maybe two months in France, every year, and I re-iterate my point that
their yellow headlights were wildly variable in colour, as seen on the
roads. My Lee numbers are from observation and memory.
>
>NOW...you are perhaps seeing the relatively recent phenomenon of the "all
>weather" headlamp bulb (or filter), which produces white light with a
>selective-yellow TINT to it. This color is legal in all countries that
>require white light, and its use is somewhat common in France now that
>selective-yellow light is no longer required.
This, I haven't noticed. Most French drivers were happy to throw away their
yellow lights. These days, a car with them is about a 50-50 chance to be
driven by an English idiot, unaware of the current rules. Some drivers fit a
yellow prism wedge, and some, for no reason I can understand, a blue one!
Frank Wood
fr...@woodf-l.dircon.co.uk
Daniel Stern Lighting
> Mea culpa! I missed the 'sealed beam'. They were better than what came
> before, but we haven't had these around for more years than I care to
> remember! The early sixties, probably.
You're fortunate.
> I have to say that individual Frenchmen are largely indifferent to
> regulations. Their yellow lights were produced in two basic ways, with
> yellow lenses, and with yellow bulbs. What happens when you mix the two?
Good point...I forgot about the IVO factor (Idiot Vehicle Owner).
> driven by an English idiot, unaware of the current rules. Some drivers fit a
> yellow prism wedge,
The idea being, presumably, to reduce dazzle to those being overtaken.
How kind of them. <shrug> Where does one find these yellow prism wedges?
>and some, for no reason I can understand, a blue one!
Because the blue glint lets them think they look like they have Xenon
headlamps?
M Carron
says...
>>>yellow light, and the color does not vary much from lamp to lamp.
>
>regulations. Their yellow lights were produced in two basic ways, with
>yellow lenses, and with yellow bulbs. What happens when you mix the two?
Was not possible:
Only H4 ( ond older 2 filaments lamps ) light were produced with yellow
bulbs ( yellow cap or dichroic filters for H4 ) and projectors for those
lamps were only produced with clear lenses.
Yellow lenses were for H1, H2 and H3 bulbes ( did not exist in yellow, at
least not before 1992 for H1 )
>spend maybe two months in France, every year, and I re-iterate my point that
>their yellow headlights were wildly variable in colour, as seen on the
>roads.
Aspect was different for normal filters or dichroic filter ( brighter ).
except for that they were all the same.
M Carron
Frank Wood
M Carron wrote in message <87eo4a$56r$1...@com36.esoc.esa.de>...
>Aspect was different for normal filters or dichroic filter ( brighter ).
>except for that they were all the same.
Observation, over twenty years and more, tells me you're wrong. Not,
perhaps, in specification, but in implementation.
Frank Wood
fr...@woodf-l.dircon.co.uk
lemon_tree
the same as the ones fitted to the Japanese cars where they have the dual
headlight system. How do I point the fog lights with the fogs this high?
(btw, can I have the distance in metres?.. thx!)
Douglas G. Cummins <DCum...@alum.calberkeley.org> wrote in message
news:3895EF8C...@alum.calberkeley.org...
> Daniel Stern Lighting wrote:
> >
> > On Sun, 30 Jan 2000, Frank Wood wrote:
> > <snip>
> >
> > > from a fog light should be wide and shallow. better than 90 degrees
wide,
> >
> > Wide, yes. "Shallow", no. The two main characteristics for a fog lamp
> > beam are width (wider = better) and a sharp horizontal cutoff at the top
> > of the beam, with minimal-to-zero light above the cutoff.
> >
> > > and maybe only 1 degree high.
> >
> > One of the main functions of a fog lamp is to provide strong forefield
> > illumination so that in worst-case conditions when you cannot see
through
> > the fog, you can see where the road is. A shallow beam doesn't get this
> > job done.
>
> Daniel, I agree with everything you have said here but wanted to
> clarify a point - the beam height should be narrow/shallow enough to
> prevent reflected glare from water and ice on the road. A beam height
> of 3 to 4 degrees with the maximum intensity around 2 degrees below
> the horizontal is common and starts illuminating around 15 to 20 feet
> in front of the vehicle (depending on how high the fog lamps are
> mounted).
>
Douglas G. Cummins
to be properly aimed when the headlamps are aimed.
The simplest method to aim your lights is to find a flat, level ground
for about 10m with a wall at least as high as your headlamps/fog
lamps. Draw a horizontal line along the wall at the height of the
bulb inside the lamp. Measure the distance between your lamps and the
wall. Draw another horizontal line below the first at 1% of your
measured distance (eg., if you're at 10m, then draw the second line
0.1m or 10cm below the first). Shine your lights on the wall and
adjust the lamps until the cutoff is between these two lines.
Technically, the cutoff line should be at the 1% line, but as long as
the cutoff doesn't go over the first line you should be fine.
The fact that the fogs are as high as your headlamps has no impact on
the aim procedure.
Douglas Cummins
Calcoast - ITL
lemon_tree wrote:
>
> I've got my fogs built into the headlight assembly on my '91 Camry which are
> the same as the ones fitted to the Japanese cars where they have the dual
> headlight system. How do I point the fog lights with the fogs this high?
> (btw, can I have the distance in metres?.. thx!)
>
> Douglas G. Cummins <DCum...@alum.calberkeley.org> wrote in message
> news:3895EF8C...@alum.calberkeley.org...
> > Daniel Stern Lighting wrote:
> > >
> > > On Sun, 30 Jan 2000, Frank Wood wrote:
> > > <snip>
> > >
> > > > from a fog light should be wide and shallow. better than 90 degrees
> wide,
> > >
> > > Wide, yes. "Shallow", no. The two main characteristics for a fog lamp
> > > beam are width (wider = better) and a sharp horizontal cutoff at the top
> > > of the beam, with minimal-to-zero light above the cutoff.
> > >
> > > > and maybe only 1 degree high.
> > >
> > > One of the main functions of a fog lamp is to provide strong forefield
> > > illumination so that in worst-case conditions when you cannot see
> through
> > > the fog, you can see where the road is. A shallow beam doesn't get this
> > > job done.
> >