firstname.lastname@example.org used his keyboard to write :
Sealed beam units, one pair had dip, one main. Another car had one pair
of combined with a separate pair of mains. Dips were always switched
off when mains were on.
My present car is a four headlight xenon job, but the dips remain on
"Harry Bloomfield"; "Esq." wrote in
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I think when I saw twin-headlight cars in the 70s with their main beams on,
all four headlights were lit, so I presume one pair of lights had twin
filament dip/main and the other pair had just main. I don't remember seeing
cars where one pair of lights went out when the other came on.
I think most of the cars that I've owned in the last 20 years have kept the
dipped filament on when the beam is on.
What was the main reason that cars changed from sealed beam to replaceable
bulb in fixed reflector? My mum's Renault 6s and my dad's later Citroen GS
in the 1970s used bulbs, but his Hillman Hunters and his Ford Sierra used
sealed beam. Maybe bulbs started out as a French (or other European) thing,
and British cars carried on for longer with sealed beam.
NY laid this down on his screen :
I think happened, when halogen lamps came along.
It began with ordinary bulbs, then along came sealed beams - which
improved massively on separate bulbs, then halogen bulbs (brighter,
whiter) demanded separate reflectors and lens again. They couldn't make
halogen work in a sealed beam unit.
I well remember my first P6 Rover - a Mk1 3500. Standard Lucas 5 3/4
sealed beams. Dips were 37 watt and pathetic. Far worse than a standard
Lucas 7" sealed beam.
Changed them to Cibie halogen units which at 55 watt were a big
improvment. Had to re-wire, so the dips stayed on with main beam.
Later, twin filament halogen bulbs became available. And with those you
could run both filaments at the same time. Arranged them so main beam had
all 8 filaments running. Half a kilowatt of light. ;-)
Had a switch so dips were either two or four filaments.
Yes. My latest car has H7 twin filament bulb and H7 single filament, in
separate housings within the headlamp/sidelight/driving light/indicator
cluster. I'm sure the dipped filament remains alight when the high beam is
Yes, just checked. There is a difference between headlights on at light
switch (when main beam is both dipped and main filament) and headlamps being
flashed with light switch off (which is only main beam filament).
But older cars with sealed beams or H4 bulbs seemed to turn the dipped
filament off when the main beam was turned on - which meant that *both*
filaments (dip and beam) were constantly being switched on and off as each
oncoming car approached (dip the headlights) and went past (back to default
state of high beam). I wonder if keeping the dipped filament on all the time
was done partly to reduce the thermal shock of it being turned on and off
all the time, as well as the more obvious advantage of providing a bit more
I always wondered why sealed beam lights became so common, given the much
higher replacement cost and the much larger object to carry around as a
spare. I suppose there was one less variable in getting the headlamp
alignment correct, in that filament was always in exactly the same place in
relation to the reflector, rather than there being a bit of variation if the
bulb wasn't perfectly seated in the reflector housing. I always wonder
whether I should get my alignment checked after changing a bulb, because of
seating variations between bulb and reflector.
Embarrassing admission. After having my car 12 years, I discovered that it
has an extra set of lights for daylight running lights, which were turned
off at a menu on the dashboard. These are dimmer-than-dipped filament bulbs
in a separate housing, rather than LED: my car is probably just too old for
LED technology to be bright enough, so they used filament.
When the (not road legal :)) 90/100W halogen conversion bulbs became
available I rigged up a relay system for my car to fit them.
I also rigged up a relay to disengage the fog light when the ignition was
off, since it seemed beyond the wit of manufacturers :)