Interesting Pacifica feature

|
|
| Think about it for two seconds:
|
| Cop car STOPPED at side of road.
|
| MOVING vehicle with blinking brake light.
|
| Notice the difference? One vehicle is stopped, one is moving.

Not necessarily. But I see the point. But it's difficult to fix a point in
space of a strobing light...you would sill nead a "steady" state aspect to it
(like perhaps a alternating bright-dim cycle...but never completely dark)

|
| The stopped cop car attracts the curiosity of passing motorists
| who gawk and naturally drive toward what they are looking at.

As do those individuals with certain medical condition, on certain medications
OR drunk that tend to be transfixed by and drawn to lights, especially
blinking/strobing ones (moving or not).

|
| The moving vehicle, the one in front of you with the blinking CHMSL, is
| doing what it can to get you off it's ass. Do any of you live in a city with
| more than 80 people in it? I mean a city where rush hour is 2 million cars
| jamming the highway and 8 lanes fo parking lot?

Yes, Washington, DC/Baltimore...7 million people.

Never yet had problems seeing the brake lights on the car in front of me as
they exist now... Never had problems before the CHMSL, to be honest. I've
never even have come close to rear ending anyone in probably close to a million
miles of driving. (But as with you, my individual perceptions/experiences are
too small a sample of data to establish policy or standard)

|
| I think some of you need to understand what real traffic chaos is all about.

Been friving for 30+ years. I think I've seen my share of traffic chaos.
Personally, having 30 cars in front of me in heavy commutuing traffic with
blinking CHMSL would certainly be added chaios in the field of vision to what
exists today. I don't think it would be helpful, in the least. Only add to
frustration and road rage for those drivers already on the edge (in my
opinion).

| Any of you seen rear ended by some blue hair who "didn't see your silver
| truck with all the lights on including the brake light"? Find yourself in a
| situation like that with 2 cracked vertabrae and some geezer saying "I
| didn't know you were stopped" and you'll be a believer in roadside
| euthanasia. That was a very congested highway and a doddering old frt going
| 60MPH while traffic was stopped.

Traffic can't be that heavy where you are if it's moving at 60MPH. Around here
every interstate is mostly stopped dead and may move 5-10 MPH for 50-60 yards
at a time every 1-2 minutes. With blinking CHMSL constantly (and I mean
constantly) on in your face for that hour or two every night? I don't think
so! Lord just thinking about it is painful!!!

| Quite frankly I don't care if my brake
| lights melt the retinas of drivers behind me as long as they stop.
|

Hard to see to stop with melted retinas!

I'm actually not saying that a strobe brake light may not be worth study. I'm
saying that none of us really know if it would do what we think (or don't
think) it would and there is a lot more to it then personal perceptions. The
general population can consist of:

o People that are color blind
o People on medications that can contribute to becoming easily confused
o People under the influence of alcohol/illegal drugs
o People with medical conditions that:
- Can easily be sent into seizures by strobes
- Easily confused/disoriented (Dementia)
- Vision impairment/cataracts (vision similar to haze on a
windshield driving into the sun...a small point of light that
will wash out their entire field of view)

....and this is just the general issues. All these things exist in the real
world and need to be factored in to understand all implications of such a
proposal. Our personal perceptions and observations in a uncontrolled
environment (yours or mine) are too small of a sample of data to make policy or
standard from (plus are subject to personal biases that skew our perceptions).
I can bet though that if you had cataracts or light vision sensitivity, you
would likely cringe at such proposals.

Remember, we all will be "blue hairs" some day and most all of us will find
ourselves with health ailments as we age, some of those ailments that _we_ will
get may be complicated by what we propose which could impact quality of _our_
life (or ability to drive) for _us_ decades from now.

 

|
| This may all be true. But its interesting that the one place I've seen a
| 'strobed' CHMSL is on the back ends of our local aid units. They have a
| center mounted red LED brake light that pulses two or three times (at
| about 10 Hz) and then stays on.
|
| They do appear to catch ones attention, since the first time I saw one,
| it was in my peripheral vision. I probably wouldn't have seen it on a
| side street except for the sudden flash. It would be particularly useful
| if one was looking in some direction other than forward when the vehicle
| in front begins braking.

I would suggest that your observation/experience in the final analysis would
show it to be counter to safety. IF such a device did to you as you described,
it inappropriately diverted your attention to a vehicle on a side street where
your attention should not have been diverted to at all...while all the while
something _could_ have been happening in front of you during that diversion
(child chasing a ball, etc.). My bet is that you would have seen a standard
brake light device in your forward field of view just as quickly as a
flashing/strobing one. (Assuming you were looking in front of you and not at
some car with a strobe light on a side street)

|
| The need to decode this flash would take more time and probably wouldn't
| help response time any. The short flicker at the onset of braking serves
| (I believe) only to attract the attention of someone who might be
| looking elsewhere and where their response might otherwise be dictated
| by how long it took them to find a track on their favorite CD.

A reasonable assumption...possibly true. Now we need to determine if the
frequency of drawing attention to something in front of you exceeds the
tendency for the device to draw your attention _away_ from things in front of
you. AND, how many things in front of you will have a strobe (to draw your
attention back) and how many of those won't (a kid or pedestrian).

 

|
| People prone to seizures should have their licenses shredded and have to
| take transit.
|
| Your arguement is stupid, to say the least.
|
|

Not at all, many of the people with these conditions can drive legally...they
are on the road right now. Only the severe cases are kept off the roads.
Therefore, that situation needs to be factored in...which means it is very
relevant. So, you suggest to create a environment where more people will be
forced not to be able to drive. That person could be you some day.

 

|
| | >
| > | > | I have to disagree with most of you guys on one thing. There will not
| > | be any confusion between a flashing brake light and turn signal light
| > | in my area of the country. Most of the dumb drivers around here are
| > | too lazy to use the latter.
| > |
| >
| > So are you suggesting different standards for different areas?
| >
|
| EXCELLENT IDEA!!! Here's my suggestion:
|
| 1) Steady red: Brake lights
| 2) Blinking amber: Turn signals
| 3) Steady Green: Accellerator pressed down in vehicle
| 4) Blinking Green: Accellerator floored in vehicle
| 5) Steady Purple: Cell phone or loud stereo in use in vehicle
| 6) Blinking Purple: Open beer container in vehicle
| 7) Steady Blue: Unrestrained children in vehicle
| 8) Blinking Blue: seatbelts not fastened in vehicle
| 9) Steady Orange: Under 18 year old driver behind wheel
| 10) Blinking Orange: Under 18 year old driver + girlfriend engaged in sexual
| relations in vehicle
|
| Ted
|
|

Sure, why not.

 

Much lower power consumption?
Much less heat production?
What LED's are we talking about here.

LEDs have some admirably attributes but 'super' efficacy is not one of them
and thermal management of any but the poorest LED arrays is problematic (and
more often than not, ignored).

There is no doubting the relative robust mechanical properties of LEDs vs
filaments but this is not a significant problem for most emergency service
vehicles.
The light output does matter - particularly where, for example, the
emergency services are on active duty on a high speed road and the beacons
are there to announce their unguarded presence.
Make it noticeable first - then pretty if you like!

At least a filament may be taken as 'on' or 'off' and not so subject to the
vagaries of time and temperature as LEDs.

I'm sure they are getting/will get there but perhaps other technologies
will overtake LEDs in the search for 'solid state' luminaires - the progress
too date has been desperately slow considering the carrot on offer.

 

Much lower power consumption, yes. Did I, uh, stutter?

That too. Here, I'll type it a third time: Much less heat production.

All of them.

I don't believe anyone in the thread's claimed LEDs to be more efficacious
than other types of light sources. They are, however, considerably more
fuel-efficient and space-efficient than several other types of light
sources. Remember, efficacy is not the same as efficiency.

The "problem" is largely theoretical, otherwise the market acceptance of
LED vehicle lighting in demanding commercial service (to say nothing of
publicly-funded traffic light service!) would be substantially poorer than
it is.

Er...yes, actually, it is. Nonfunctioning lighting on a commercial or
emergency vehicle = downtime. Downtime = expense. Greatly extended
lifespan compared to filament light sources is one of the prime motivators
behind the rapid adoption of LED devices on commercial and emergency
vehicles. Perhaps the situation is different in the UK, but the majority
of freight trucks ("goods lorries" to you), buses ("coaches") and
emergency vehicles in North America are at least partially LED-equipped,
if not fully LED-equipped.

Yes, this is why there exist government standards for the performance of
vehicular lighting and signalling devices. LED devices must meet the same
standards as other devices. So again, you're describing a problem that
does not exist.

They're already here.

Heck, no. The performance of LED emitters is increasing at a sizzling
(and accelerating) pace.

DS

 

Daniel, you are correct. LED-based traffic signals are all over the place and
almost all delivery trucks/trailers and buses have been equipped (perhaps
retrofitted) with LED-based lighting. This seems to have occured over the past
1-2 years. They are very bright and visable, even on a bright summer day.
Seems to me they've figured these things out.

I noticed some Cadillac and Infinity models are using molded LED arrays now as
well.

 

For lumen per cc LEDs are the poorest light source available excepting the
very dim 'indicator' type filaments.

I remember efficacy as lumen per watt: efficiency is ....

Unfortunately the problem is not largely theoretical - it is however largely
ignored - supported by a lay beleif that LEDs are incredibly efiicient, and
last for thousand upon thousand of hours.
LED degradation is unknown

How and when is the degradation of these LED sources monitored?

 

I must be missing something here. If LEDs are not more efficacious
than other types of light sources, how can they be "considerably more
fuel-efficient". Which "fuel" are you talking about. The gasoline that
provides energy to the engine in the car that drives the generator
that powers the lights? If so, the efficacy and fuel-efficiency should
go hand-in-hand.

 

Honda USA management bragged about Americanizing the cars by going toward
all red rear lights. I stopped buying Hondas; that was just one reason.

Richard.

 

Efficacy: The amount of light out per unit of electrical power in.
Typically expressed as lumens per watt (lpw).

Fuel-efficiency: The amount of fuel used to do a specific job, expressed
in units of fuel per unit-task achieved, or in unit-tasks achieved per
unit of fuel. An example is "miles (travelled) per gallon" or "litres per
100 kilometres (travelled)".

Sometimes a lighting device has high efficiency and high efficacy at the
same time, but not always. Take, for instance, the example of a brake lamp
on the rear of a truck trailer that takes standard 4" round rear light
units:

A) A unit using an 1157 bulb, which consumes 27 watts in "bright" mode and
8 watts in "dim" mode. The assembly produces 25 axial candela in the dim
taillamp mode, and 200 axial candela in the bright brake lamp mode.

B) A six-LED unit which consumes 4.2 watts in "bright" mode and 0.42 watts
in "dim" mode. The assembly produces 25 axial candela in the dim taillamp
mode, and 200 axial candela in the bright brake lamp mode.

Obviously, unit B is more fuel-efficient, because less power is consumed
to do the same job with unit B than with unit A.

The efficacy of the filament bulb is in the range of 15 to 20 lpw, but in
order to use this light source for a brake/tail lamp, the light must be
filtered red. In so doing, a large amount of the light from the bulb is
lost, so system efficacy drops to around 3 or 4 lpw.

The efficacy of the LEDs typically used in such a lamp is up in the 20 to
30 lpw range, and virtually all of the light produced is of the correct
color without additional filtration. So in the case of this example, the
efficacy is also high.

But now suppose we want to move to the front of the vehicle and look at
headlamps. There, no color filtration is required and we're comparing
white LEDs, which are currently reaching for 22 lpw, to a tungsten-halogen
lamp at up to 33 lpw. Prototype LED headlamps have been built, though
they're still a number of years away from mass production. Perhaps by the
time the LED peel-and-stick headlamp becomes a reality (the prediction is
currently around the 2008 model year), white LEDs will have surpassed
tungsten-halogen lamps in efficacy.

More on this topic in Don Klipstein's article here:

http://members.misty.com/don/lede.html

DS

 

Yes, that is correct. You must include any required filter in your
"efficacy" calculations when comparing colored light sources. So,
efficacy still follows efficiency.

Perhaps or perhaps not, but what does the possibility of LED headlamps
in 2008 have to do with the issue if efficacy vs. efficiency? If and
when LED headlamps arrive they will be more fuel-efficienct than other
sources only if they are also more efficacious.

Interesting article but I don't see any claims here that efficacy does
not follow efficiency.

 

Gee, whiz, I guess we better hurry and remove the strobes from all those
emergency vehicles pronto! Who knows, the mass population-wide epileptic
seizure attack could be just around the corner! Think of the disaster we
could avert! Write Congress!!!

--Geoff
(f*** the strobes, I want "attack lasers" behind my grille...)

 

Daniel is apparently considered enough of an authority by those folks that
know
better as to be able to derive a living consulting about lighting. You
might check
his website out:

http://www.danielsternlighting.com/

When you setup a similar website and are able to make money off the subject
of
lighting, then you are free to claim a similar amount of "weight" for your
opinions
on lighting.

I do agree that DS's website needs a bit more of a biography, though.

Ted

 

And guess what - when every vehicle has a strobed brake light on it, there
won't
BE any advantage to having one. It's like the center-mounted brake light
story.
That story goes something like this:

Once upon a time a man had a plan - let's put center-mounted brake lights
on cars to reduce rear-end collisions. So the man with the plan created a
study
to justify it. The study mounted 1000 cars with center-brake lights and
sent them
out into the world. After a while the study concluded that yes, indeed,
center-mounted
brake lights reduced rear end collisions. Flush with excitement the man
with the
plan convinced the worlds governments to mandate center mounted brake
lights.

30 years later all cars had center mounted brake lights. Then one day
another man
had another plan.- let's remove the center-mounted brake lights
on cars to reduce rear-end collisions. So the man with the plan created a
study
to justify it. The study took 1000 cars with center-brake lights and
disabled the
lights and sent them out into the world. After a while the study concluded
that yes,
indeed, removing center-mounted brake lights reduced rear end collisions.
Flush
with excitement the man with the
plan convinced the worlds governments to mandate no center mounted brake
lights.

Then a little boy said "Man, aren't the results of your study simply because
the cars that lack the center mounted brake light are _different_ than all
other cars on
the road, and thus attract attention because they are different, thus
forcing the drivers
following the car to pay more attention because subconsciously they realize
that something
isn't right about the car they are following"

Then all the man with the plan's friends shouted "pay no attention to the
little boy behind
the curtain that saw through the smoke and mirrors"

Ted

 

That boat and trailer has never seen water! ;-)

Ted

 

Failing to see the brake lights isn't what causes rear ends, in my opinion
(and
experience, being both the rear ender, and rear endee.)

The primary cause of rear enders is when the traffic has _tremendous_
variance
in speed. You don't have this in heavy traffic. Where you have it is in
traffic
that is moderate and starts to oscillate. A simple observation of waveforms
in springs, which you should have had in high school, easily illustrates
this.

When traffic oscillates (ie: accordians), you have many situations happening
all of the time where
people are driving 40-60Mph in one minute, and 60 seconds later are driving
2-4Mph,
then another 60 seconds later are back at the 40-60Mph range, as they pass
through
the leading then the trailing edge of the traffic "wave" Much work has been
done by
traffic engineers to try and dampen out oscillations of traffic on
freeways - in fact
the simple entrance ramp light is one of the tricks used to break up blocks
of
traffic that would normally hit the freeway and can trigger an oscillation.
But
despite what is done, every major road has locations where when time of day
or weather conditions are right, oscillations can start.

Most of the time most of the drivers are able to stop quickly enough that a
rear end collision doesen't
happen. But when you have a vehicle that has extremely good stopping
ability - such as
a light weight vehicle with ABS on a wet road - being followed by a vehicle
that has
poor stopping ability - such as a heavily-loaded truck on the same road, and
the
traffic is thick enough so that it is impossible to maintain a safe
following distance (because
vehicles that try to do so get constantly cut in front of, thus no matter
what they do the
buffer does not hold) then all you need is an oscillation, and BANG, rear
end collision time.

Ted

 

With light bars that have multiple, eletronically synchronized fixed flashers,
are they (and their greater mechanical complexity) really even necessary
anymore?

Not much less noticeable. Roof racks already look like light bars at any
distance. And I'd say that reduced drag is quite a bit more important than wind
noise level. Old lightbars like the Federal Signal TwinSonic (the big square
'70s CHP bar seen in all those old cop shows) could take as much as 10 MPH off
the top end of the car and increase 0-100 times by 15 seconds. A single
rotating beacon is figured by the MSP to only cost 1-2mph, they still use just
the one Unity RV2 on the roof. The real benefit of the low-profile LED bar is
in getting the drag down to that level.


--Aardwolf.

 

13) Kid who has clear light lenses on the back of the CIVIC and the
bulb are dipped in so much fingernail polish/paint and everything
looks so dim because you can't see the bulb light up when the brakes
are hit.

14) People who have dark tint covers on headlights and tail lights.
The tail light covers are so dark that during the day, you can't see
the light when they come on, even when you are right behind them.

 

On Sat, 03 Jan 2004 04:10:31 GMT, Victor Roberts

[snip]

[snip]

Let me add a comment that I thought was obvious when I wrote the
original reply, but now think may be now be so obvious at all.

Efficacy and efficiency are proportional only when considering light
sources (including any filters) that have the same SPD. Obviously a
light source that converts 10% of its input power to yellow light will
produce more lumens per watt than a light source that converts 10% of
its input power to blue light or red light.

This thread seemed to be about sources that produced the same "color"
of narrow-band light. While this does not insure equivalent SPDs, they
are probably close enough that efficacy should be proportional to
efficiency, with an error that is a function of the mismatch between
the two source SPDs.