Why no rear lights with DRLs?
 

Here in Minnesota state law says lights must be on when driving in rain
or impaired visibility. Lots of folks with DRLs ignore this, saying,
hey, my DRLs take care of that. But on many (most?) cars with DRLs, the
lights are only on in the front.

I think rear lights are more needed in these conditions than front ones.
Many times in freeway driving I am following someone in an adjacent
lane, and through heavy spray I suddenly make out a car in front of me,
barely visible, with no lights on. This is especially bad when the car
is a medium grey- it blends in well with the asphalt.

Why did the manufacturers elect to only light front lights? I think
DRLs are a safety hazard, as it causes drivers not to turn on lights
they really need, assuming that their DRLs take care of everything.

Can't speak for all cars, but the three Volvo's I've owned turn rear
lights on along with front ones, either DRL or normal.

Sweden has had DRL since the early 70:s and most manufacturers (all?)
run the tail lights with DRL. Some leave out the instrument lights,
possibly as a reminder to the driver to turn the lights on fully at
night.

Thomas

In article <1114091006.18e90d32a8f7726e7d0860cd353154ab@teran ews>,
says...
>
>
>Here in Minnesota state law says lights must be on when driving in rain
>or impaired visibility. Lots of folks with DRLs ignore this, saying,
>hey, my DRLs take care of that. But on many (most?) cars with DRLs, the
>lights are only on in the front.

Another reason why DRL's are a stupid idea.
------------
Alex

On Thu, 21 Apr 2005, Don Stauffer wrote:

> Here in Minnesota state law says lights must be on when driving in rain
> or impaired visibility. Lots of folks with DRLs ignore this, saying,
> hey, my DRLs take care of that. But on many (most?) cars with DRLs, the
> lights are only on in the front.

Yeah, that's one of the many problems with headlamp-based DRLs. They fool
drivers into thinking their car has "automatic headlamps", so they drive
around at night and in poor weather with only the DRLs, which provide
insufficient forward visibility and/or excessive glare, and no presence
marking from the sides and rear.

> I think rear lights are more needed in these conditions than front ones.

Both are needed. So are properly-set-up red rear fogs, but in the words of
one of the North American regulators, "The automakers will never let us
require those".

> Why did the manufacturers elect to only light front lights? I think
> DRLs are a safety hazard, as it causes drivers not to turn on lights
> they really need, assuming that their DRLs take care of everything.

It's an implementation problem, not a conceptual problem. The law says
that the parkers, tails and markers CANNOT come on with the DRLs unless:

1) The DRLs are full-intensity low beam headlamps, or

2) The vehicle is equipped with automatic light control that turns on the
full-intensity headlamps when ambient light conditions call for it.

Manufacturers shy away from (1) because it causes short effective low-beam
bulb life, and they're dumb enough in the North American market to include
bulbs in new-vehicle warranties (this is also why low-performing "Long
Life" bulb variants are used in most North American OE installations)

Manufacturers use (2) on some of their higher-end cars, but they shy away
from it on mass-market cars 'cause they like to be able to charge extra
money for the "feature" of automatic light control.

Really, for lots of reasons, headlamp-based DRLs are the wrong way to do
it.

DS

Also, taillamps on with DRLs in bright daylight reduces the off/on
contrast of brake lights and front turn signals.

DS

I more or less agree, Daniel.

I dont know if you are speaking to Canadian law, or whether those points
apply in the USA as well.

DRL's are, IMHO, better than nothing at all, even if the tail lights do not
activate,
but if would be better if the systems were fully automatic.

So many idiots ignore the law here in Texas which says that you should
activate your headlights in rain, after legal dark, etc. Many never do it
except in darkest night..

There are kits available which reduce the current to the headlights and turn
on lights whenever the key is on, BUT I don't think these activate
taillights.

I was thinking about homebrewing a system, but will continue to just turn on
my headlights manually for the time being.

My latest Volvo has lights that are almost completelt automated. It
has a sensor that decided when DRL should replace the xenon
headlights, and it decides separately when the dash lights should go to
full bright or allow variable dimming.

On Thu, 21 Apr 2005, HLS wrote:

> I more or less agree, Daniel.
>
> I dont know if you are speaking to Canadian law, or whether those points
> apply in the USA as well.

The US and Canadian DRL standards are almost identical.

> DRL's are, IMHO, better than nothing at all, even if the tail lights do
> not activate, but if would be better if the systems were fully
> automatic.

No, it would be better if the systems were designed to optimize the DRL
function and encourage proper, rather than improper, driver operation of
vehicle lighting systems.

DS

"Daniel J. Stern" > wrote in message
.umich.edu...
>
> Also, taillamps on with DRLs in bright daylight reduces the off/on
> contrast of brake lights and front turn signals.
>
> DS
>

Probably why Volvo has separate brake lamps from running lamps.