OT: LED versus sodium street lamps

[terry.shitcrumbs]

I was driving through the suburbs of Sheffield last night- a city that is c urrently in the process of changing its street lamps from sodium/orange col oured illumination to bright white LED.

Having a mixture of the two systems and with my driving route presenting a good opportunity to experience them both, from one street to the next, in a variety of settings, I was surprised at my very clear preference for the o ld sodium lamps. Previously, I would have said that the bright white of LED s ought to provide better illumination for driving.

What I noticed, with the LEDs, is that they cast a very localised pool of b right white light directly under the lamp post and showed little spread, co mpared to sodium lamps. The result of this is that the dark adaptation of m y eyes was ruined by passing directly under an LED street lamp, after which , I was immediately plunged into poor illumination. Perhaps this might be a voided by fitting a much greater number of LED street lamps per unit length of road, but it seems that the council has merely effected like-for-like r eplacement. I suppose that beam-spreading lenses might also be a solution.

Beyond the issue of the spread of the illumination, another issue that was very apparent was the excessive contrast caused by the harsh white light, c ompared to sodium light. Under LED street lamp illumination, certain featur es of the road and roadside were (to my 42-year old eyes) picked out very s harply, but at the expense of others. Anything white or somewhat reflective was dazzlingly bright and anything dull was all but invisible. The road ou tline could clearly be seen on those rare sections of road on which the lin e paint is in good condition, but the tarmac surface itself and the pavemen t were not so easy to see. I can imagine this presenting a real danger for pedestrians in dark clothing, or in those circumstances in which a drunken bozo sits down at the kerbside, for a rest (I have come across this many ti mes).

Have other people noticed problems with LED streetlamp illumination, or is it just me?

Regards,

Terry.

[Tim Streater]

No, they have simply fitted bulbs with a narrow light cone. When I was replacing the GU10 halogens in the kitchen, I got a couple of CFLs, and SWMBO immediately pointed out what you have observed: the light cone was too narrow. So when buying a set for the kitchen, I took care to get 120deg ones or whatever it is. I soon replaced those with LEDs due to the slow-on that the CFLs exhibited, but made sure that the LEDs were wide angle too.

[CB]

Certainly not just you. And loads more issues than you identified

Although some people will disagree with you about the colour rendering

[Brian Gaff]

Not just you. I've been told by many drivers that the LEDs though apparently brighter kind of pull at the eyes somewhat, whatever that means. I suspect it has something to do with the strange colour balance or something. Its apparently like those pale blue ones we used to have at one time, what were they, Mercury vapour? The poor reach I'd imagine is to comply with light pollution standards which are much more stringent than when the sodium were put in, and as you say it will need more lights to cope with this. Kind of self defeating if you need more lamps than before, you might as well have kept the Sodium ones until the lamp columns needed replacing. Brian

[Dave Liquorice]

Yep, alternate pools of light and dark. Woe betide anything dark in the dark pool...

I don't like the colour either, there is something not right with "daylight" at low lux levels. This may just be conditioning from 50+ years of incandescant but it might be more fundemental, coming from fire/candle/lamp light... Red light doesn't bugger your night vision, why? There must be an evolutionary reason for that, maybe it's so you can see the tigers creeping up by firelight or flaming torch light...

Or perhaps the council have been sold a pup by the supplier. "Oh yes, the light level is the same for far less power", whilst quietly omitting that that light level is as measured directly below the luminaire and also forgetting the affect of beam angle. Councillers who approve these things are not engineers and the council has probably "outsourced" anything technical.

A beam spreading lens would reduce the light level below the luminaire, below te required specification? So you need an more powerful light source. You can't get something for nothing...

[Tim Streater]

That's because the only time we see daylight at low lux levels is during an eclipse of the sun. Try it when more than 90% of the sun is obscured, as I saw it in 1999 in France. Normally when natural light levels are that low, it's because the sun is low in the sky, and the light colour is then markedly different to full daylight.

[Tim Lamb]

In message , Dave Liquorice writes

Not sure where I got the idea but don't sodium street light luminaires direct more light away from oncoming traffic?

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[Dave Liquorice]

Full moon is "daylight" at low lux levels as well. But yes the low light level during a partial eclipse of the sun is also disquieting and it doesn't take much. There was a minor partial elcipse here on

29th March 2006 and even that reduction in light level was noticeable and a bit "weird".

TBH I might be remebering 1st Aug 2008 (40% across N.Scotland, 20% SW England). But put 20th March 2015 in your diaries:

Roughly 0830 to 1030 for the entire event.

That as well. Of course full moon light is not bright enough for us to have colour vision so the fact that moonlight doesn't feel "wrong" is not surprising.

[DerbyBorn]

"Brian Gaff" wrote in news:m7e9h1$f6r$ [e-mail]:

I agree that old lamps should be kept until they really need replacing. However, I think that councils are racing each other with the latest fad in order to get a "tick in a box" on some sort of Councils Environmental Survey.

I find LEDs appear bright - yet the effect of the brightness seems minimal. Is this something to do with the area of a filament (or discharge tube) compared with the size of an LED- plus the old lamps had a reflector to add the light from the back of the filament or tube.

[Brian Gaff]

Not being able to see them myself, its hard to say, but I understand that there is a big push to stop light pollution. The steeper angle is probably to do with that, I'd imagine. I've not heard of any council box ticking, but there was a debate a while back on whether to replace bulbs after x hours of use on a planned basis, or wait till they went phut. The snag of course with the gas discharge type is that the glass became blackened and the light reduced but for the same consumption, so it was decided to use manufacturers suggested average life and replace ona rolling basis, though of course some do go down prematurely. I do find that many people who use magnifiers with led lights in them, though they are muchlonger lasting than a bulb, the glare effect is very tiring and this is on straight DC from a battery, so that was why I suspected it was the balance, ie spectrum of the light which is causing the eye to be confused by some very bright parts but dim parts as well, which maybe stop some colours from looking bright under them.

Brian

[Brian Gaff]

I seem to recall somebody at the council telling me about some replacement bulbs that were, in fact three bulbs each with a tilt, so that in effect you had three pools of light from one lamp. However my thought was that this may well dazzle a driver as they come along. It sounds like the problems are known about but nobody has a solution yet.

Brian

[Brian Gaff]

I remember the last eclipse. I could still see a bit and was intrigued with the light projecting little pictures of the Eclipse though the leaves of the trees onto the ground underneath. Brian

[Tim Streater]

Pin-hole camera.

[harryagain]

Having a mixture of the two systems and with my driving route presenting a good opportunity to experience them both, from one street to the next, in a variety of settings, I was surprised at my very clear preference for the old sodium lamps. Previously, I would have said that the bright white of LEDs ought to provide better illumination for driving.

What I noticed, with the LEDs, is that they cast a very localised pool of bright white light directly under the lamp post and showed little spread, compared to sodium lamps. The result of this is that the dark adaptation of my eyes was ruined by passing directly under an LED street lamp, after which, I was immediately plunged into poor illumination. Perhaps this might be avoided by fitting a much greater number of LED street lamps per unit length of road, but it seems that the council has merely effected like-for-like replacement. I suppose that beam-spreading lenses might also be a solution.

Beyond the issue of the spread of the illumination, another issue that was very apparent was the excessive contrast caused by the harsh white light, compared to sodium light. Under LED street lamp illumination, certain features of the road and roadside were (to my 42-year old eyes) picked out very sharply, but at the expense of others. Anything white or somewhat reflective was dazzlingly bright and anything dull was all but invisible. The road outline could clearly be seen on those rare sections of road on which the line paint is in good condition, but the tarmac surface itself and the pavement were not so easy to see. I can imagine this presenting a real danger for pedestrians in dark clothing, or in those circumstances in which a drunken bozo sits down at the kerbside, for a rest (I have come across this many times).

Have other people noticed problems with LED streetlamp illumination, or is it just me?

They have fitted the wrong lanterns. They are designed for a specific height/distance ratio. Sounds like the ones you saw are on poles too short. (or too far apart), depending one the level of illumination wanted.

They might have used the old poles or u/ground wiring to save money.

[polygonum]

There are two sorts of sodium street lamp - the old "pure" sodium and the more recent pinky ones (which I think are high pressure?). There is already a huge difference between them.

On the M4 near Reading, the LED section has been done well in my opinion. Even, very little spill, good colour. But as you say, some areas they have been fitted with far less consideration.

In a brand new Morrison's local shop, they have them in the car park on very low poles. Initially looks as if they might be OK, but when you drive in they start alternately blinding you and leaving you in the dark

- and similarly when walking.

But LEDs are also used in other places on or by roads. Near here there is a pedestrian crossing of the newer type where there is a light on the pole at about waist height. The red light there must be driven at 50 or

100 Hz - if, when waiting at the lights, you sweep your eyes across, you see dozens or more images of the red light. That is really annoying!

[Dave Plowman (News)]

I doubt there is much low pressure sodium still in use. It was very narrow spectrum light making many colours appear the same.

[Dave Liquorice]

Narrow as in monochromatic! Pretty sure it's a single emmision line.

Plenty in use around here, those that are still working that is. Been naff all maintenance for a while and about 50% of the lights in town are out or come on for a minute then off for a few minutes. Not helped by ENW slowly removing all "foreign" equipment from their poles as a BT engineer was killed whilst working on a shared pole.

[Dave Liquorice]

One of the few bits of A level Maths I remember as possibly "being useful" was how to calculate the height/spacing of lamp posts to give even illumination below them. I think it might have assumed an omni directional light source but you still have to account for the inverse square law and light contributions to a given point on the ground from distant posts...

These days I expect the buyer doesn't have to worry about that, just install the luminaires at the specified height and spacing and it "just works".

[polygonum]

[Chris French]

In message , "Dave Plowman (News)" writes

Plenty round here (rural Cambridgeshire), though they are now being repalced with LED's

AIUI the county council got some extra money from the Gov or the EU specifically for changing to LED streetlights.

So I've been experiencing them both quite a bit lately.

My take:

I prefer the 'white' light to the old orange of the LP sodium lamps. Yes, there is a bit more pooling of light under the lamps, but I can't say I ever thought it was really affecting how I can see. I don't seem to notice it so much now, which suggests it was just different and I've just got used to it.

The only thing I dislike about them really is that I can sometimes get this little bright flash it the top of my eye as I approach the light, just for a split second. Which can be a bit irritating.

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