Interesting Pacifica feature

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).

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.

| > 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)".

Yep.

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:

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:

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.

[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.