Genre: Enclosed Horizontal Traverse Low Pressure Sodium Lantern
The low pressure sodium discharge lamp was developed by Philips in 1932. After two successful trial installations
(including the first low pressure sodium installation in the UK along the Purley Way, Croydon) the first commercial installation
was installed by Liverpool Council in 1933 using specially commissioned lanterns from Wardle.
The development of lanterns continued through the 1930s and accelerated when it was determined that the lamp’s brightness and
its long length made it less susceptible to glare. Lanterns with bare bulbs suspended over an overhead reflector (the so-called "seagull" lanterns)
quickly followed. Glass manufacturers were initially slow as the first plate refractors for low pressure sodium lamps didn’t appear
until the end of the decade.
The advantages and disadvantages of low pressure sodium were readily debated, especially when an alternative (the medium and high
pressure mercury discharge lamp) was also available. The monochromatic light was considered especially useful for arterial
and traffic routes, the lamp’s shape cast a wide beam across the road surface, the light was also considered more penetrating
in foggy conditions and it was the most efficient light source being manufactured. However, the light was also considered
inappropriate for high streets, promenades, civic areas and residential streets and so some lighting engineers
restricted its use to traffic routes only. Therefore low pressure sodium became known as "the drivers’ lamp."
The arrival of plate glass refractors resulted in large lanterns made of metal frames enclosing heavy glass sheets.
These bulky lanterns continued to be made into the 1950s until being usurped by lanterns with plastic bowls and
machined or moulded plastic refractor plates. The lanterns were still large; the size dictated by the bulky
control gear, but their design and construction was becoming simpler.
The 1950s and 1960s saw huge improvements in the construction and efficacy of low pressure sodium. Early two-piece
designs (dubbed SO) were replaced by the one-piece, more efficient integral design (called the SOI). The development of
linear sodium (SLI) broke the one hundred lumens per watt barrier, lead to a radical rewriting of the British Standards
of street lighting and prompted the development of new families of streamlined lanterns. But it wasn’t until the arrival
of a new heat-reflecting technology (called SOX) that a cheap family of extremely efficient bulbs became available.
The energy crisis of the 1970s saw a rethink in street lighting and lamp efficiency became dominant when fuel was both
in short supply and expensive. This saw the large scale removal of colour corrected high pressure mercury, fluorescent and
ancient tungsten lamps by low pressure sodium replacements. The old arguments that the smoky-orange lamps were inappropriate
for residential areas no longer applied. By the end of the 1980s, low pressure sodium was the dominant street lighting lamp used in the UK.
The use of low pressure sodium came under scrutiny again. High pressure sodium, finally developed as a viable technology in the
1960s, was coming of age and offered a compromise of slightly less efficacy with better colour rendering. Questions were
being asked about the physiology of the eye and visual adaptation under low lighting levels; previously the wavelength
of low pressure sodium had been deemed the most suitable, but research now suggested that the eye responded better to white
light. Concerns were raised about light pollution and the low pressure sodium lamp was seen to be the chief culprit
(although it was more to do with older non-cutoff and semi-cutoff optical designs rather than the lamp itself).
By the turn of the century, the age of low pressure sodium was seen as coming to an end. Research in white light technologies,
especially metal halide and a renewed interest in compact fluorescent coupled with the advantages of using white light at
low lighting levels, saw the end of the low pressure sodium lamp’s dominance. Its use was discouraged in the specifications,
lantern manufacturers started to wind down their production and bulb manufacturers followed suit.
By the end of the first decade of the 2000s, low pressure sodium was in stark decline, and less and less of the UK’s
streets were being lit by its characteristic orange glow.
Name: Phosco P125
Date: Mid 1950s - Mid 1960s
Dimensions: Length: 18 7/8", Width: 12 3/8", Height: 9 ¾"
Light Distibution: Non Cut-Off (BSCP 1004 Part Two:1956)
Lamp: 55W SOX
By the mid 1950s, the rebuilding of the UK’s infrastructure was proceeding at full speed, and many new companies
appeared who were eager to pick up the various lucrative relighting contracts. Phosware (later Phosco) were founded by
Concrete Utilities; the firm were experiencing unprecedented demands for their concrete columns (as the use of steel for street lighting
was still restricted) and decided to branch out into lantern manufacturer as well.
Their first low-pressure sodium lanterns were simple open-types, but the firm soon developed a family of enclosed low-pressure sodiums. This
family were typified by their aluminium canopies, wide and deep Perspex bowls (designed to accommodate the huge bulky gear of the era),
vertical refractor grooves at the end of the bowls, and overhanging lip which accommodated the “Oddie Key” (a unique bowl fastening mechanism
only used by Phosco).
The lanterns were initially quite successful and were featured in many of Phosware’s advertisements. The main road version, designed to
take 85W-140W SO/H (later 90W SOX) was the most successful, but the smaller side road versions also saw service.
By modern standards, the lanterns were huge. As soon as gear sizes were reduced, Phosware were quick to replace the range with the P152
series; this shared the characteristics of the earlier family but were smaller. This allowed Phosware to cut down on raw material costs
for manufacturing. For a while, both ranges were advertised side-by-side (particularly in the early 1960s), but the P120 range
was gradually run down and discontinued.
The P125 was the side-entry version of the lantern, designed to take a 60W SO/H bulb.
The Phosco P125 wasn’t a particularly popular lantern. It was used by some local authorities for residential and side-street lighting, but these installations were relatively rare.
The lantern is easily identified by its size and profile. Furthermore the vertical grooves in the end of the bowl and the
use of an Oddie key are unique PhosWare characteristics. The maker’s name and
model number are not cast into the outer lower lip of the canopy unlike its smaller counterparts.
The main beams of the lantern were formed by two large plate refractors which extended down either side of the
plastic bowl. The lamp was mounted centrally so it engaged directly with the refractors (unlike the smaller models
which had a lower mounted lamp and the refractors interacted with flux reflected from the overhead reflector).
The vertical refractors at either end were designed to spread the light in azimuth. This would’ve spread the light back
onto pavements or further across the road.
The lantern didn’t have an overhead reflector. The interior was painted white to reflect back any light emitted above the lamp.
There was no spreading refractor in the base of the bowl. The large flat base simply allowed the light from the lamp to
illuminate the area directly beneath the lantern.
The lantern doesn’t take gear. The gear at the time was large and bulky and would’ve added considerably
to the dimensions of the lantern.
The Phosco P125 In My Collection
This lantern was given to me by Darren and was originally installed somewhere in Northamptonshire.
This shot clearly shows the vertical refractor grooves at the end of the lantern. This was a PhosWare standard
design for all their early lanterns. It was designed to spread the flux in azimuth, spreading the small amount of light
emitted from the ends of the bulb.
Despite years in service, the lantern was still in good condition. The bowl was just starting to go cloudy; the
interior required some repainting and the canopy still bore traces of the original bronze paint. The photocell
was a later addition.
The bowl was secured by one Oddie key situated at the street end of the lantern. As this required space (for both
the key and its engaging mechanism), the end of the canopy extended slightly past the bowl, which gave the lantern its unique appearance.
There were no maker’s marks or logos on the top of the canopy. The original bronze finish had almost completely gone. The lantern had also been painted silver at some point in the past.
The three key areas of the refractor bowl can be seen in this shot: the vertical grooves at the bowl ends to spread
the light emitted; the main refractor panels which fashioned the two main beams; and the frosted base which acted as a diffuser
and scattered the light emitted below the lantern.
This shot clearly shows how the Perspex bowl was placed in a metal holder which was secured by an Oddie
key at the street end of the lantern and hinged at the house end. Sometimes PhosWare added their name
and lantern model number to the extruded lip beyond the canopy of the lantern but this wasn’t the case for this lantern.
The interior of the lantern was extremely simple. The canopy had several extruded lugs for components to be fitted;
interestingly the wide lug to support the lamp holder assembly was cast at either end of the lantern, therefore potentially
offering two lamp positions. Other components included cable ties, terminal strip blocks and cable clamps.
The lantern was secured by two Allen bolts in the spigot.
Phosco P125: As Aquired
The numbering scheme suggests the P125 was one of Phosco's earlier SO/H lanterns, coming between the
first, bulky gear-in-head lanterns (the P120 through P123) and their less bulky replacements
(the P152 and P153).
As a non gear-in-head lantern, it was probably designed for aesthetic appeal, being far more streamline than its contemporaries. However
retains the classic Phosware design choices of vertical grooved refractor patterns on the end of the bowl,
overhanging canopy over the bowl and Oddie key.
This example stood somewhere in the Northamptonshire area and was replaced by Darren in 2008.