"Chris J Dixon" wrote in message
...
NY wrote:

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.

You mean that twin filament bulbs are using both simultaneously?

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
on.

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
light.

What was the main reason that cars changed from sealed beam to replaceable
bulb in fixed reflector?

I think the cost of replacement was too high. Also it was a
design constraint, you were stuck with a standard shape.

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.