Low pressure sodium lamps now hard to find.

[whole diary]

[broadgage]

Sometimes known as "sox" lamps.
The last factory making these closed last year and availability is now declining.
Mainly used for outdoor lighting, roads, footpaths, yards, car parks and the like.

If you are involved in a heritage railway, or indeed in any other enterprise that uses these lamps, time to buy a few spares, or consider alternatives.
LED retrofits are available. These are fine for everyday illumination but do not look right if an original appearance is desired.

[Godfrey Tables]

I collect light bulbs. This is not something I thought I'd ever admit to in public, and probably puts me fairly high on the nerd scale.
A few years ago I bought a few SOX lamps, along with a means to drive them, to add to my collection.

With the way LED's are going, I don't think it'll be long before High pressure sodium, Mercury, Metal Halide and even fluorescent go the same way. Although for heritage purposes these might be easier to simulate with cleverly disguised LEDs solutions.

Some time ago at the Peak Rail heritage railway in Matlock I found gas mantles simulated with incandescent pygmy lamps. These are probably LED as well now...

[Bmblbzzz]

Are we talking about the yellow-orange ones? If so, I was thinking about them just the other day. That they used to be everywhere and now they're quite rare. Until a couple of years ago there were still a few streets near here with them, but now they've been replaced with (white) LEDs. For which I'm quite glad. Why would you want to replicate that colour-sapping dull yellow glow?

I collect light bulbs. This is not something I thought I'd ever admit to in public, and probably puts me fairly high on the nerd scale.

But you score highly on self-awareness!  By the way, do you have a brother called Bobby!

[stuving]

Some time ago at the Peak Rail heritage railway in Matlock I found gas mantles simulated with incandescent pygmy lamps. These are probably LED as well now...

For heritage purposes, do you want your new (sustainable?) lamp to simulate HPS or sodium, or the mercury vapour lamps that they replaced (with no attempt at simulation whatever), or the previous incandescent lamps, or the original oil lamps? Or what came before that - presumably darkness?

[broadgage]

Are we talking about the yellow-orange ones? If so, I was thinking about them just the other day. That they used to be everywhere and now they're quite rare. Until a couple of years ago there were still a few streets near here with them, but now they've been replaced with (white) LEDs. For which I'm quite glad. Why would you want to replicate that colour-sapping dull yellow glow?

I collect light bulbs. This is not something I thought I'd ever admit to in public, and probably puts me fairly high on the nerd scale.

But you score highly on self-awareness!  By the way, do you have a brother called Bobby!

The lamps that are no longer manufactured are low pressure sodium, these give a deep orange/yellow light without any colour rendering. Not normally considered to be an attractive light, but some heritage locations may prefer them in order to look traditional, they have been in general use for at least 60 years.
If the original appearance is not required, LED retrofit lamps are available.

High pressure sodium lamps, often known as SON lamps, are still manufactured and remain very popular. They give a lighter golden yellow light, this badly distorts colours but does allow some colour rendering.
I doubt that many new fixtures for SON lamps are being installed, but there is a considerable demand for replacement lamps for existing equipment.

[TonyK]

Many councils are actively changing sodium lighting for LEDs. Some are citing lower maintenance costs, and a 60% saving on electricity. Central government is encouraging this with grants. They are also more versatile, with some having the ability to dim at certain periods of night. All told, it looks like the end for that yellow-orange glow. I wonder if that colour, a very narrow band of the spectrum, can be emulated by a LED light?

[ellendune]

Many councils are actively changing sodium lighting for LEDs. Some are citing lower maintenance costs, and a 60% saving on electricity. Central government is encouraging this with grants.

Swindon currently is currently 6 months into an 18 month program to change all its lights. Not only the saving on electricity but in changing lamps.  When I was last involved in street lighting (ok so 40 years ago now but the SON was the modern technology then) lamps needed changing every 2 years. 

They are also more versatile, with some having the ability to dim at certain periods of night.

Benefits of reduced light pollution which is known to affect wildlife.

All told, it looks like the end for that yellow-orange glow. I wonder if that colour, a very narrow band of the spectrum, can be emulated by a LED light?

Yes it can, as easy as white actually. AIUI^▸ (as I understand it) colours can be produced by mixing native Red Blue and Green, but white light produced this way is not good.  Yellow and White can be better produced with a UV LED by fluorescence. The different coatings can produce a very blue white light or a yellow, mixing them allows a range of whites and if required a yellow.

[stuving]

Many councils are actively changing sodium lighting for LEDs. Some are citing lower maintenance costs, and a 60% saving on electricity. Central government is encouraging this with grants. They are also more versatile, with some having the ability to dim at certain periods of night. All told, it looks like the end for that yellow-orange glow. I wonder if that colour, a very narrow band of the spectrum, can be emulated by a LED light?

Depends how close you look at the light! Astronomers were relatively happy with the light pollution from the original sodium lamps, as the light was confined to the two narrow spectral lines characteristic of sodium. So while the lamps and luminaires may have been quite bad for the amount of light they chucked about, it could be filtered out within instruments leaving most of the spectrum clear for observations. At high pressures, the sodium vapour emits a broad spread of light across much of the visible spectrum that doesn't allow that to be done. Hence the astronomers were really hacked off by that change.

You can't get good colour rendering in a lamp with narrow spectral lines, so the flourescent phosphors are chosen to give the broad spread required for that - leading to more upset astronomers. And then along comes Elon Musk as well ...

LEDs are more directional, which helps, but that's a quite modest factor compared to a good filter. I don't expect we'll see the Milky Way making a return to our urban skies.

[TonyK]

I don't expect we'll see the Milky Way making a return to our urban skies.

One of the bigger advantages of living on the edge of a small Devon village, with a massive amount of sky available to me, is that I can often see the Milky Way. In Bristol, I couldn't often see more that a dozen stars.

[Bmblbzzz]

In Bristol, I couldn't often see more that a dozen stars.

You just need to hang around the Hippodrome. 

[johnneyw]

In Bristol, I couldn't often see more that a dozen stars.

You just need to hang around the Hippodrome. 

Or late night refreshment at Renato's Taverna dell'Artista....The hostelry of preference for the theatre casts and crews after last curtain....or at least it was when I frequented it all those years back.

[Trowres]

My short road currently has one LED, 2 low pressure sodium and one high pressure sodium lamps.

BG^▸ (Brake Gangway (carriage))'s post has caused me to look at the nearest LP example with the same feeling I would reserve for a disappearing locomotive class 

[MVR S&T]

Oh, do those tall posts have a function, having only been allowed out for shopping, then going to/from work, not seen a lit street light since March, though they are stating to come on under the trees on my back from after work shopping now.

[broadgage]

If anyone wants a low pressure sodium lamp, these can still be found on fleabay but stocks are declining and prices increasing.
If you wish to light a low pressure sodium lamp, it is VITAL not to connect it directly to the mains, the correct control gear MUST be used, also available on line.
Low pressure sodium lamps usually have a standard bayonet cap, but this does NOT mean that they should be inserted into standard mains lamp sockets.
Most types must be operated horizontally, or nearly so.

[Electric train]

I am not sure that SOX were that common on station platforms the colour being to close that of a yellow aspect, all the station lighting I was involved back in the 1980's was MBFU or tungsten-halogen with some rare place with plan incandescent tungsten.

LED lamps come in a wide range or colour temperatures and further colour adjustment could be done with photographic / theatre lighting gel. 

The energy saving of LED for a heritage railway could be substantial from a 40W to 100W or higher SON to 11W to 25W LED

Just as a side note the large (1960's) sliver shaded lights at Paddington station (removed in the 1990's) were 1000W MBFU and there was about 100 of them ............... I know I changed a fair few lamps and replace a number of ballasts back in the 80's