I miss low pressure sodium street lights

[Truvelo]

I miss SOX and Mercury - we still have some SOX on the back roads and courts of the sixties ex-Naval estate i live on together with the odd Mercury one in the concrete walkways and “nooks and crannies”.

But they and the SONs are slowly but surely being replaced by LEDs and CFTs which I hate.

What does CFT mean?

I assume you mean CFL - compact fluorescent. These have also nibbled away at SOX and SON's share of the market but these too have succumbed to the success of LED.

[ManomayLR]

I miss SOX and Mercury - we still have some SOX on the back roads and courts of the sixties ex-Naval estate i live on together with the odd Mercury one in the concrete walkways and “nooks and crannies”.

But they and the SONs are slowly but surely being replaced by LEDs and CFTs which I hate.

What does CFT mean?

I assume you mean CFL - compact fluorescent. These have also nibbled away at SOX and SON's share of the market but these too have succumbed to the success of LED.

But why did LPS get more expensive? And if LPS was so efficient, why did people favor HPS? I've heard of HID (high-intensity discharge) but what does this really mean? And how does it differ from LPS or HPS?

[Patrick Harper]

But what was the main thing that led to the end of LPS?

From the early 90s onwards, SON and other HID sources slowly nibbled away at SOX's market share, largely due to much better colour rendering. At the advent of mass-market LED lanterns in 2008, the split between SON and SOX in the UK was around 50/50. SOX has declined much faster since then due to the end of production of SOX equipment and the rising cost of SOX lamps, which by then negated any benefit in reduced energy consumption. LEDs may have hastened their demise but even without them, it was only a matter of time anyway.

On motorways, how many working LPS installations remain?

The longest stretch by far is M4 J40-44 (Wales).

As of last year there were two stretches on the M60, one from J17-18 and one from J24-25, plus a very brief stretch under J1. I think J17-18 is being or has been replaced by now.

Western end of the M58.

Various sliproads around the M61 at Kearsley.

A74(M) J22 Spur

M6 J22-23

Some slips at Croft (M6/M62)

Most slips at Thorpe (M25/M3)

Vestiges on the M1 near Kegworth?

Southern end of M69.

M1 J15a is probably going or gone as part of the smart motorway works there.

This list may well be optimistic as some of these may well have been switched off permanently, as M1 J5-6a has, or removed since the Google van last came round. There's numerous mostly-unlit sliproads with perhaps a few SOX lights where they meet the exit or entry-point. The newest 'set' of SOX lights on the UK motorway network is this at A1(M) J6, from circa. 2013.

[Truvelo]

What does CFT mean?

I assume you mean CFL - compact fluorescent. These have also nibbled away at SOX and SON's share of the market but these too have succumbed to the success of LED.

But why did LPS get more expensive? And if LPS was so efficient, why did people favor HPS? I've heard of HID (high-intensity discharge) but what does this really mean? And how does it differ from LPS or HPS?

LPS probably got more expensive due to falling demand. And as for the transition from LPS-HPS-CFL/LED each one has better colour rendition than the previous. CFL/LED are about the same. Obviously colour must have been more important than running costs.

By the late 80s LPS had started falling out of favour and until 2000 I thought everything would end up being HPS but then CFL started making an appearance. Certainly here in Staffordshire CFL was being installed en-masse in the early 2000s but then LED started making inroads.

[ManomayLR]

From the early 90s onwards, SON and other HID sources slowly nibbled away at SOX's market share, largely due to much better colour rendering. At the advent of mass-market LED lanterns in 2008, the split between SON and SOX in the UK was around 50/50. SOX has declined much faster since then due to the end of production of SOX equipment and the rising cost of SOX lamps, which by then negated any benefit in reduced energy consumption. LEDs may have hastened their demise but even without them, it was only a matter of time anyway.

On motorways, how many working LPS installations remain?

The longest stretch by far is M4 J40-44 (Wales).

As of last year there were two stretches on the M60, one from J17-18 and one from J24-25, plus a very brief stretch under J1. I think J17-18 is being or has been replaced by now.

Western end of the M58.

Various sliproads around the M61 at Kearsley.

A74(M) J22 Spur

M6 J22-23

Some slips at Croft (M6/M62)

Most slips at Thorpe (M25/M3)

Vestiges on the M1 near Kegworth?

Southern end of M69.

M1 J15a is probably going or gone as part of the smart motorway works there.

This list may well be optimistic as some of these may well have been switched off permanently, as M1 J5-6a has, or removed since the Google van last came round. There's numerous mostly-unlit sliproads with perhaps a few SOX lights where they meet the exit or entry-point. The newest 'set' of SOX lights on the UK motorway network is this at A1(M) J6, from circa. 2013.

There's LPS on the A1 on the short stretch from Rowley Green to South Mimms Interchange. But LPS is now completely out of production (last year saw Philips manufacture its last few bulbs, the last manufacturer of LPS bulbs), so it's only a matter of time until we see them go, and the last bit of bright yellow is wiped from my everyday life.

The difference between LPS and LED in terms of color temperature and visibility is clear - take a look at this photo from Philips, promoting LED replacement bulbs for LPS lighting fixtures.

[image changed to URL for copyright reasons]

[Patrick Harper]

I missed A1(M) J3-4. It appears J2-3 was switched off.

[nowster]

HID is High Intensity Discharge. In essence a mini carbon arc lamp. Very blue, needs a UV filter.

Street lamps went through a phase with LEDs where they were "cool white", which isn't great for circadian rhythms. Warmer colour temperatures, but with good colour rendering index, closer to the Boltzmann distribution of an incandescent lamp (or sunlight around sunset/sunrise), would be more ideal.

[traffic-light-man]

Without wanting to 'be that guy', bulbs are planted in the ground...

In our industry, Philips stopped the manufacture of a tungsten halogen lamp type of which they were the sole manufacturer. Another company, Ushio began manufacturing the lamps almost immediately in response. There was most definitely a market for those lamps, though, the fixtures they were designed for a still fairly common throughout the world.

As Truvelo mentioned upthread regarding lamps becoming more expensive as demand lessens - we also happened to see a common-as-muck lamp type increase significantly in cost, with progressively fewer manufacturers over a relatively short space of time. That was a case of the cheap fixtures these cheap lamps went in were also the ones used most often by those on a budget, and for those folks, the cheap LED fixtures gave a much better deal. That's left the portion of the industry with a requirement for these lamps paying the price - quite literally.

HID is indeed High Intensity Discharge. SON, SOX, Halide and Mercury are all HIDs, though.

[ManomayLR]

This is the story of Flagstaff, Arizona - a city that has gone back to the days of the yellow glow - but with an amber LED source (phosphor converted amber) that gives an old-school LPS look with LED technology.

I just got a huge craving for nostalgia. Even just a little bit on the M25 will remind me of when I was 5...

[Gareth]

That's an interesting article.

Perhaps the most interesting bit is about LEDs having a more directional light and so the lux can be focused where it is intended, allowing replacement LEDs to have a lower lumen output compared to the SOX/SON lamps they replace. I think this is ultimately the answer when it comes to the trade off between light pollution and the ambiance of the public realm.

In fact, it is largely what's been happening, hence Bryn noticing more stars. It's mostly been down to cheapskatey procurement rather than any concern about light pollution but it's still a broadly welcome thing.

Another thing that isn't considered enough is the perceived brightness of streetlighting to the human eye. White light simply seems brighter to single wavelength light of a similar intensity. As a kid there were still pockets of mercury lighting hanging on in some parts of the city. My area wasn't one of them but there was the odd street where you'd find one or two hanging on. I specifically recall one street near me which had just one midway down amongst the otherwise SOX hegemony. It looked much brighter. It was near trees and as you walked up the street towards it, you'd see a greenish glow amongst the vegetation, along with a moonlight glow along the ground near it. Then you would suddenly be bathed in the moonlight colour was you walked passed only to return again into the murky orange sodium night.

The thing is though, it wasn't actually brighter. It was a 80w MBFU bulb kicking out around 3800L in a road other lit with 35w SOX emitting around 4550L. So it was actually dimmer, as well as consuming more than double the power of the SOX lights. But clearly the much wider spectrum was telling my brain that it was receiving more information.

I do think if implemented right, LEDs can mean less light pollution, less power consumption, a nicer ambiance than SOX and no perceived loss of brightness to the person on the street. It just needs to be designed correctly.

[scott125]

Still plenty in Glasgow , though the main roads are now mostly LED , still plenty of old SOX stuff.

[ManomayLR]

But I still struggle to understand, if LPS was so popular and so efficient, why was there any need at all to get rid of it? Did it have any significant drawbacks? And so why were authorities so keen to switch to HPS/metal halide/CFL?

[Al__S]

LED's can be made in virtually any colour temperature so 1800K is possible which would emulate SOX. There are companies, Philips I believe, producing LED replacement bulbs to fit in a SOX chassis.

but there would be a big difference in colour perception between an RGB set of LEDs emulating SOX yellow and a narrowband LED that's tuned to almost exactly 589nm (to replicate a SOX lamp's 589.0 and 589.6 nm twin emission lines). Those two spectral lines were why filtering was very easy- you just need to filter for those two wavelengths.

[traffic-light-man]

But I still struggle to understand, if LPS was so popular and so efficient, why was there any need at all to get rid of it? Did it have any significant drawbacks? And so why were authorities so keen to switch to HPS/metal halide/CFL?

SOX was popular because as a replacement to an incandescent lamp, it was far superior in terms of efficiency. A trade off being that on the whole, it made everything black and yellow and a bit grim. In essence, only things that are able to reflect the specific wavelength of the SOX output provide any kind of contrast meaning the colour rendering is completely bias to that wavelength - everything else remains dark. Your dark clothed pedestrian by the roadside hedgerow wasn't very obvious at all, because their navy jacket, blue trousers and the leaves and branches won't reflect the light, so it all appears as a dark mass.

As attitudes to safety and technologies changed, SON lamps became more bang-for-buck when looking beyond solely the efficiency factor. And on the whole, they're still very much efficient and cost effective compared with other lamp technologies that existed at that stage. They emit a wider spectrum of light increasing the colour rendering of the streetscape, more items have the opportunity to reflect the light and their colour, thus it becomes safer for the road user.

When the Knowsley MBC/SSE Lighting PFI began around ten years ago, SON was the lamp type of choice. LED was not mainstream, and from a PFI point of view, probably cost prohibitive at that stage. For the more troubled areas of the borough, they went with White-SON and CFL for roads and footways respectively, purely based on the fact it was a white output. I think that was fairly standard at that time given the tools available.

I think the reason SOX remained favourable in certain areas was down to the efficiency factor and a stock legacy. White output LED fixtures have finally ticked all of the boxes from a highways point of view, so have become the de-facto standard on all road classes in all settings.

There's obviously a lot more factors at play, too, such as the superiority of wider-spectrum light meaning that in some instances less fixtures are required, which all adds to the efficiency factor of newer (than SOX) technologies.

[thatapanydude]

I will miss SOX too, much prefer it to the LED's we have now !! Still working but patchy on the A1 from Sandy to Baldock and Wittering.

[ManomayLR]

I will miss SOX too, much prefer it to the LED's we have now !! Still working but patchy on the A1 from Sandy to Baldock and Wittering.

It might sound weird but LPS on the M25 was a beautiful thing. I have been on the A1M near Hatfield at night, and also the A1 very close to me, and being bathed in yellow for a few minutes gives me undoubted nostalgia. From the top floor of the house I can just about make out the LPS on the A1. Since the last manufacturer of LPS bulbs discontinued from last year (meaning no more LPS bulbs are being produced at all) it means all LPS bulbs will be replaced with a different type at end of life, likely LED but HPS is still an option.

[DB617]

I have huge nostalgia for LPS as I grew up in the late 90s and early 2000s, when South Glamorgan was still almost 100% LPS with a few HPS/mercury replacements where I assume fittings had critically failed. I have particularly vivid happy memories of the ten-minute drive home from my Grandparents' house at night, where I would squeeze my eyes tightly shut and imagine the lights were blinking (the light on my eyes would dim and brighten as our 306's sunroof passed under each lamp) to show us the way home. Then the unlit section of road around the runway at Cardiff Airport, all of a minute's drive, I would try to doze off so that my Dad would carry me inside to bed. Good times. It's really strange, the things we associate with our childhood good times, be it music, roads, smells, you name it.

[ManomayLR]

I have huge nostalgia for LPS as I grew up in the late 90s and early 2000s, when South Glamorgan was still almost 100% LPS with a few HPS/mercury replacements where I assume fittings had critically failed. I have particularly vivid happy memories of the ten-minute drive home from my Grandparents' house at night, where I would squeeze my eyes tightly shut and imagine the lights were blinking (the light on my eyes would dim and brighten as our 306's sunroof passed under each lamp) to show us the way home. Then the unlit section of road around the runway at Cardiff Airport, all of a minute's drive, I would try to doze off so that my Dad would carry me inside to bed. Good times. It's really strange, the things we associate with our childhood good times, be it music, roads, smells, you name it.

I remember falling asleep in the car as a child (in the late 2000 decade), and when my parents woke me up, there would be an LPS light above my head, bathing me in yellow as I tiredly trudged into the house. I remember there would be two LPS lights that had large, brick-like lamps on thick concrete poles, and the rest would be modern tube LPS on steel poles.

Looking at Street View, it was all replaced by LED when we moved out. Our new road has HPS but it's only a matter of time until LED comes here too.

[Patrick Harper]

HID is indeed High Intensity Discharge. SON, SOX, Halide and Mercury are all HIDs, though.

I stand corrected, I used 'HID' in the sense of HPD (high pressure discharge).

[ManomayLR]

HID is indeed High Intensity Discharge. SON, SOX, Halide and Mercury are all HIDs, though.

I stand corrected, I used 'HID' in the sense of HPD (high pressure discharge).

I have never heard of the latter.
Also, what is this so-called white HPS lamp? Never heard of it before.