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Author Topic: LED street lighting  (Read 16898 times)

paul.fr

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LED street lighting
« on: 30/08/2007 14:05:15 »
Is it possible? would this be more cost effective than the present lighting?


 

another_someone

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LED street lighting
« Reply #1 on: 30/08/2007 17:37:30 »
Not sure that the present sodium lighting is particularly inefficient.

At present, LED lighting suffers from not having a very high maximum power output (street lights have to produce a great deal of light), and are still very expensive (all coming out of our taxes).  Also, I am not sure that using so much silicon is such a good idea (it is a very useful material, but it can be overused - I have seen it mentioned that for every 1Kg of electronic grade silicon produced, one produces 2Kg of CO2 as a byproduct).
 

Offline Bored chemist

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LED street lighting
« Reply #2 on: 30/08/2007 20:24:06 »
What silicon?
LEDs are made of things like gallium arsenide. The energy cost of producing them is high but they last for a very long time. It might just make sense to replace street lights with LEDS and, as the cost of energy continues to rise, the case gets better all the time.
 

another_someone

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LED street lighting
« Reply #3 on: 31/08/2007 00:24:40 »
What silicon?
LEDs are made of things like gallium arsenide. The energy cost of producing them is high but they last for a very long time. It might just make sense to replace street lights with LEDS and, as the cost of energy continues to rise, the case gets better all the time.

But would one have enough gallium to satisfy the demand of changing every street light on the planet to LED lights.  How much GaAs does one need in a single light to create a light output equivalent to what is presently produced by a sodium light?

Are sodium lights really that inefficient that one would notice any significant increase in efficiency in using GaAs LEDs in their place?
 

Offline Soul Surfer

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LED street lighting
« Reply #4 on: 02/09/2007 10:37:52 »
Sodium lamps approach the maximum theoretical illumination per watt of energy input at the expense of having a very restricted colour range.  LEDs are unlikely ever to achieve this efficiency.
 

Offline techmind

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« Reply #5 on: 02/10/2007 00:32:29 »
As Soul-Surfer says, there is a theoretical maximum efficiency of a lightsource which also relates to its spectrum and hence ability to resolve colour. The theoretical upper limit is 683 lumens per Watt (lm/W), and such a lamp would be a monochromatic green and would not resolve any colours. (A Lumen is the correct way to measure visually-useful light). The theoretical maximum efficiency decreases as you cross the colour spectrum from green towards either red or violet. The maximum theoretical efficiency for the 589nm monochromatic sodium colour is about 525lm/W.
I believe real-world low-pressure sodium lamps are somewhere around 200lm/W; being monochromatic they don't resolve any colours.

For a bright red (610nm), the maximum theoretical efficiency is about 340lm/W. The eye is not very sensitive to deep blue light, so 470nm (close to a TV-screen blue) has a maximum theoretical efficiency of only 60lm/W. (These numbers come from the CIE "Y" function, also known as visual efficacy.)

For a white light you need a mixture of different wavelengths, and you can argue about the theoretical maximum efficiency till the cows come home, because it all depends on exactly what kind of white you want, and how well you want it to reproduce colours. You can trade-off theoretical efficiency against accuracy of rendering object-colours.

The best white(ish) fluorescent lamps and white(ish) LEDs are currently around 100-120lm/W. LEDs are unlikely to be used for streetlamps for some time as they cannot yet be made big enough to handle the overall power (and light intensity) needed for large-area lighting at a cost-efficient price point.

Existing low- and high-pressure sodium lamps can handle powers of several hundred watts, and are a tried, tested, and economical technology. Sodium lamps are proven to withstand the outdoor environment and consequent wide temperature ranges.
« Last Edit: 02/10/2007 00:36:13 by techmind »
 

Offline ukmicky

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LED street lighting
« Reply #6 on: 02/10/2007 21:49:29 »
Is it possible? would this be more cost effective than the present lighting?
Yes it is possible as you can purchase them, dont know how good they are though.

wonder if they can use Xenon gas in street lights as they seem all the rage with cars.
 

Offline pirunner

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« Reply #7 on: 04/10/2007 00:04:01 »
Do sodium lights give off any heat? This could also be another factor in efficiency.
 

Offline techmind

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« Reply #8 on: 04/10/2007 19:09:02 »
Do sodium lights give off any heat? This could also be another factor in efficiency.
Of course they do. The difference between the theoretical efficiency and the real-world efficiency of something invariably comes out as heat. Possibly 50% of the energy put into sodium lamps comes out as heat. But that's still better than anything else available, practical, and economically viable.

LEDs get hot too! A major part of the technological progress which has enabled us to have high-powered LEDs in the past decade is advancements in thermal-design (i.e. heatsinking) of the LED chip. Put a few watts into anything and it'll get hot!
 

Offline McQueen

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LED street lighting
« Reply #9 on: 06/10/2007 15:44:03 »
I bought a small hand held torch that works with a cluster of LED's, it is much better than a normal torch, is practically indestructible and the battery lasts for much longer.
 

lyner

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LED street lighting
« Reply #10 on: 06/10/2007 23:06:05 »
LEDs are more efficient than a filament and, at low power and low volts, better  and easier to drive than fluorescent tubes.
They seem to be the way to go when low light output is needed for torches, boat navigation lights and 'night lights'.
 

Offline daveshorts

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LED street lighting
« Reply #11 on: 29/10/2007 10:05:34 »
wonder if they can use Xenon gas in street lights as they seem all the rage with cars.
I doubt it, as they are unlikely to be as efficient as a sodium lamp because they are emmitting more light in the blue where our eyes are less sensitive.

I also wish they were banned from cars, as while they may be great if you're doing the driving, they are horrible for everyone else. They are much more dazzling (apart form anything else they are twice as bright) they are whiter so ruin your night vision more, and they change colour as you drive past which is very distracting. I have no idea why they were allowed in the first place.
 

another_someone

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LED street lighting
« Reply #12 on: 29/10/2007 13:30:21 »
As you say, xenon lights do give a broader spectrum.  This may well reduce their theoretical efficiency, but on the other hand, they do give some improved colour vision, which must be a benefit (after all, the purpose of illuminating an object is to provide information about that object, and the more information one can gleen, the better one can judge a situation).

The issue of glare would seem to be about producing lenses that are suitable for the light source you have.
 

lyner

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LED street lighting
« Reply #13 on: 29/10/2007 23:02:41 »
Quote
on the other hand, they do give some improved colour vision, which must be a benefit
When driving a car, however, you have different requirements for your vision than when you are in a situation where colour vision is a benefit. You have to deal with a very contrasty scene and startlingly bright blue lights are a serious disadvantage for this. The beam pattern that you can get with point source QI bulbs can be much better controlled than using the old frame type filaments. But the high intensity in the centre of the beam can seriously affect the vision of oncoming drivers., when it hits them, even briefly.
The new lamps are a damned nuisance, in many ways.
 

another_someone

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LED street lighting
« Reply #14 on: 30/10/2007 02:32:50 »
When driving a car, however, you have different requirements for your vision than when you are in a situation where colour vision is a benefit. You have to deal with a very contrasty scene and startlingly bright blue lights are a serious disadvantage for this. The beam pattern that you can get with point source QI bulbs can be much better controlled than using the old frame type filaments. But the high intensity in the centre of the beam can seriously affect the vision of oncoming drivers., when it hits them, even briefly.
The new lamps are a damned nuisance, in many ways.

But is the problem with the blueness, or with the brightness, or with the shape and direction of the beam?

I don't see a problem with the blueness (unless we are to condemn the emergency services).  The problem with the strength and shape of the beam is another matter.

I do not disagree with the problems with xenon beams, but I don't see the colour as being the issue.
 

lyner

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LED street lighting
« Reply #15 on: 30/10/2007 12:12:56 »
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(unless we are to condemn the emergency services
Yes - I do!. The flashing lights are much too bright at night and actually cause pain!!
They should be modulated to suite the time of day. Who knows how many minor accidents they have caused due to the needless distraction?
The 'new' lamps have point source filaments and that has a big effect on the reflector design and on beam pattern and contrast. Notice how most modern cars have tiny headlamps - because the filament is tiny and they can be made to work at that size.  Good for the driver - bad for everyone else.
The colour is an issue because, at night, your eyes are adapted to low light levels and excessive blue light levels spoil your vision.  If you want to navigate a boat safely at night, it is usual to have only red lighting on board. A hint of a bright blue light and you are back to square one.
I am not interested in getting a good match for my jumper or the paint in my hallway when I am driving home at midnight. I want to see as much as possible of the road and its dangers. Horses for courses.
If you wanted to provide daylight conditions all over the road all night then you would have the environmentalists after you - and rightly so,
 

another_someone

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LED street lighting
« Reply #16 on: 30/10/2007 14:23:57 »
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(unless we are to condemn the emergency services
Yes - I do!. The flashing lights are much too bright at night and actually cause pain!!

Not a problem I have noticed (I certainly don't find the red lights any easier).

What I do have a problem with is flashing LEDs on bicycles (they may be red, but their small size, and flashing nature - not their brightness as such - does cause me problems).



The 'new' lamps have point source filaments and that has a big effect on the reflector design and on beam pattern and contrast. Notice how most modern cars have tiny headlamps - because the filament is tiny and they can be made to work at that size.  Good for the driver - bad for everyone else.

I don't see the small reflector size as being particularly beneficial to drivers, but I would imagine they are cheaper to manufacture, less likely to be damaged by debris being thrown up at them (they present smaller targets, and possibly would be stronger), and would improve the aerodynamics of the car.  As you say, a larger reflector would make the light more tollerable for oncoming traffic, and on that point I do not disagree.



The colour is an issue because, at night, your eyes are adapted to low light levels and excessive blue light levels spoil your vision.  If you want to navigate a boat safely at night, it is usual to have only red lighting on board.

But you would not be using the red light to illuminate the environment you are trying to navigate through.  In theory, when driving at night, you should be driving in a manner where you can stop within the distance illuminated by your headlamps (a criteria that is very different from the use of lights at sea).  Nobody would suggest using red searchlights at sea, since searchlights are intended for environmental illumination.

I am not interested in getting a good match for my jumper or the paint in my hallway when I am driving home at midnight. I want to see as much as possible of the road and its dangers. Horses for courses.

No, but in the absence of colour information, the only visual information you have is visual brightness, and two objects of similar brightness cannot be distinguished, although they may be of different colour, and the colour information could be used to separate the object better.  It is not colour fidelity that I am concerned with, but merely to be able to better distinguish that are of different colour but similar brightness (and so better understand the environment you are driving in, and so better understand the hazards within that environment).
 

lyner

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LED street lighting
« Reply #17 on: 30/10/2007 14:51:10 »
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But you would not be using the red light to illuminate the environment you are trying to navigate through.
That is not my point. My point is that other road users (that includes you and me) will be subject to impared vision as a result of blue headlights.
Quote
Nobody would suggest using red searchlights at sea, since searchlights are intended for environmental illumination.
The use of ANY searchlight at sea is potentially a great nuisance because of what it does to other users. You use them in emergency, only  - not for the other 364 days of the year.  In a rescue, you have effectively blinded your rescuee completely, once you have shone a searchlight onto his boat. The same situation occurs when you get an eyefull of one of these high intensity (particularly the blue) headlamps.
Let's face it, the reason that people like the blue lights is nothing to do with the visibility issue- it's because they look new and sexy.

The fact is that other people are involved in this issue - not  just the driver of the car!
« Last Edit: 30/10/2007 15:04:36 by sophiecentaur »
 

another_someone

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LED street lighting
« Reply #18 on: 30/10/2007 16:25:46 »
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But you would not be using the red light to illuminate the environment you are trying to navigate through.
That is not my point. My point is that other road users (that includes you and me) will be subject to impared vision as a result of blue headlights.

But your comment was that there is no benefit to the primary user (the driver) of having colour vision available at night - my argument is that such an advantage does exist.

Equally, monochromatic red lights can still remain a hazard to other road users, hence the objection to using rear fog lights (which are red) when it is not foggy.

I am not trying to argue for arbitrarily bright head lights (although at time when there is no oncoming traffic, there are clearly benefits in using full beam lights, but they should be dipped in the presence of oncoming traffic), I am merely arguing for the benefits in having wide spectrum lights.  In fact, it may even be argued that since colour information additional information over and above the pure brightness information you may obtain with monochromatic light, that you would need brighter monochromatic lights just so that you can gain more detailed brightness information to offset the lack of colour information.  Ofcourse, I suppose we could avoid the whole issue if drivers were to drive with night vision goggles, and so obviate the need for headlamps at all.

Incidentally, it is not as simple as saying that using bright headlights is only beneficial to the driver, and a problem for other road users.  I, as a road user, not only use the light of my own headlights, but use the light of other people's headlight - whether it is to illuminate the road ahead of me beyond the range of my headlight, or to see the backscatter of headlights on a damp day giving me advance warned of a car coming over the brow of a hill, or to see the reflection of oncoming headlights on the bushes on the side of the road as I approach a blind bend.  This is not to dent that as I approach close to oncoming traffic, if that traffic has too strong a headlight, or badly adjusted headlights, that it cannot cause dazzle, but only to say that at other times, the strong lights of other cars can still remain a benefit to me.

 

lyner

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LED street lighting
« Reply #19 on: 30/10/2007 23:59:06 »
But, if the disbenefits to others outweigh the benefits to ourselves, what should we do?

Monochromaticity has nothing to do with rear fog lamps - it's the excessive brightness. Nobody is bothered by the normal rear lamps.

Are there, in fact, many situations where the actual ability to distinguish between subtle differences in colour is important in night driving? Red, green and amber  lights  or reflectors are  easy to spot  and anyone wearing dark coloured clothes - whatever the shade -  is not going to be seen., in any case

I am merely recommending  a balanced approach in which no one car driver inflicts his requirements on others. If on-coming drivers simply have to jack up the brightness of their lights in order to compensate from being dazzled that's just war. It's the same argument as is used against 4X4s; they are merely a  selfish luxury for most people.

Night vision goggles would be fine but they are not fail safe and they are expensive and (you may recall) they are very much MONOCHROMATIC displays and low resolution.

Other peoples' excessively strong lights don't  help you  to see them any  more than modest lights. If everyone had the same light power, that would be the best solution.

I think that you will find that far more accidents have been caused by dazzlement than  by fainter than average headlights on other cars.

Let's just agree that all lights should, at least, be properly adjusted and that rear fog lamps should be illegal (enforced) in anything but extreme poor viz.
 

another_someone

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LED street lighting
« Reply #20 on: 31/10/2007 01:32:52 »
Monochromaticity has nothing to do with rear fog lamps - it's the excessive brightness. Nobody is bothered by the normal rear lamps.

Not disagreeing - was merely saying that the monochromaticity was not a cure either.

Are there, in fact, many situations where the actual ability to distinguish between subtle differences in colour is important in night driving? Red, green and amber  lights  or reflectors are  easy to spot  and anyone wearing dark coloured clothes - whatever the shade -  is not going to be seen., in any case

Have to say that to date I have been able to avoid hitting people with dark clothing as well, although sometimes with not much margin to spare - and in those cases, colour can be a big help.  Even just seeing an unlit car parked against some pushes, same problem, and colour can help.

But, if the disbenefits to others outweigh the benefits to ourselves, what should we do?
I am merely recommending  a balanced approach in which no one car driver inflicts his requirements on others.

The nature of driving is that each drivers needs will often conflict with another drivers needs, but I do not disagree that that inevitably requires compromise.

The problem is further exacerbated by the fact that each driver has their own strengths and weaknesses, and so what bothers one driver may not bother another.

If on-coming drivers simply have to jack up the brightness of their lights in order to compensate from being dazzled that's just war.

Never really found that if I am being dazzled, then pushing up my lights really helps at all.

Night vision goggles would be fine but they are not fail safe and they are expensive and (you may recall) they are very much MONOCHROMATIC displays and low resolution.

agreed - and I believe they e not recommended for use above 50mph.  The idea was somewhat whimsical.

Other peoples' excessively strong lights don't  help you  to see them any  more than modest lights. If everyone had the same light power, that would be the best solution.

It depends on the situation.

If one is driving along a long straight road, where one has direct vision for oncoming cars, then I would agree.

On the other hand, when one is driving in situations where direct vision of oncoming vehicles is limited, and one is relying a lot on reflected light (e.g. backscatter from humid air, or reflections around corners), then the stronger the other cars lights, the sooner you will see them (and until they are coming straight at you, you should not very likely be dazzled by the lights).

But I think have to differentiate between cars that are using full beam (when no other car should be obviously in their line of site), and when a car should be using dipped beam to avoid dazzling oncoming traffic.

Let's just agree that all lights should, at least, be properly adjusted and that rear fog lamps should be illegal (enforced) in anything but extreme poor viz.

I have no problem with that.
 

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LED street lighting
« Reply #20 on: 31/10/2007 01:32:52 »

 

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