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 lampís 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 didnít 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 lampís 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 driversí 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 wasnít 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 lampís 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 UKís
streets were being lit by its characteristic orange glow.
Name: Simplex Aries
Date: Early 1970s - Late 1980s
Dimensions: Length: 54.5cm, Width: 18.4cm, Height: 17.2cm
Light Distibution: Semi Cut-Off (BS 4533)
Lamp: 35-55W SOX
In the early 1970s, Relite introduced two new ranges of residential, side-road sodium lighting. The energy crisis
had prompted many authorities to swap out their inefficient GLS and HPMV stock, and sales of low-pressure sodium lanterns were
steadily growing. Plus new developments in materials, such as glass fibre, and component manufacturing, such as smaller gear,
allowed smaller lanterns to be designed and made.
These two ranges were typical of the time. Both were originally marketed as the New Sodium lanterns. A streamlined
lantern with glass reinforced plastic (GRP) body was offered in two sizes but was limited to side entry only; whilst a more
conventional, blockly lantern with canopy cast from aluminium alloy was available in side and top entry options. Both lanterns
gained their astrological names shortly afterwards, a nod towards a naming scheme originally instigated by REVO over
a decade perilously, and were called the Aries and Gemini.
Both the Aries and Gemini took the same refractor bowl, thus reinforcing the family connection
between them. The Gemini was gear-in-head as standard, whilst the Aries offered it as an option. (The
gear in the Aries was fitted to a hinged gear tray which doubled up an over-reflector). Additionally the
Aries was offered in two different sizes: a tiny and sleek 35W option, and a longer 55W option. Due to its size,
the 35W Aries was fitted with a slightly smaller refractor bowl, which omitted the characteristic vertical groves
of the larger models.
Both lanterns were kept on catalogue, and retained their names, when Relite was sold to Simplex.
During this period, the Aries was also sold as industrial security lighting with integral gear and one-part photocell. This was marketed and
packaged as the Simplex Shadow Shifter Security Lantern.
Both lanterns remained on catalogue until the demise of Simplex. Some of the companyís designs
were later produced by Whitecroft but the Aries and Gemini were discontinued.
It was a relatively popular lantern and could be found installed throughout the country. As one of the
smallest low-pressure sodium lanterns produced, it was obviously popular for its slender outline and size.
The lantern is easily identified by the unique refractor pattern cast along its bowl. A short section of vertical
prisms gives way to the long horizontal prisms which form the main beam. Only the Gemini shared a similar bowl, but
the Gemini had a flatter canopy, and far bulkier appearance.
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.
The vertical refractors at the pavement side of the lantern were designed to spread the light in azimuth. This
wouldíve spread the light back onto pavements. (The smaller 35W version of the lantern omitted this part of the
The lantern didnít have an overhead reflector. The glass reinforced plastic of the canopy was white anyway so it
could reflect back any light emitted above the lamp.
There was no spreading refractor in the base of the bowl. The narrow flat base simply allowed the light from the lamp to
illuminate the area directly beneath the lantern.
Gear was an optional extra and was carried on a hinged gear tray.
The Simplex Aries In My Collection
I purchased this lantern from fellow collector Claire Pendrous. The original installation location of
the lantern was unknown, but it had been in service for many years, and was relatively dirty and unmaintained. The
only restoration required was a strip down, thorough cleaning, and reassembly.
Even though it was the larger 55W version, the lantern appeared extremely small and sleek. It had a very compact design
and itís hard to believe that gear could be accommodated as an option as well.
Despite years in service, the lantern was still in good condition. After a good cleaning, the only indication of the lanternís long service life was its yellowing
The bowl was hinged on the traffic facing side of the lantern with the toggle clips on the other.
The canopy was flat and unadorned with makerís name or logos. A large extruded cylindrical area provided a convenient
mounting place for an optional photoelectric cell.
As this was the larger 55W version, the bowl included the characteristic vertical grooves at the pavement side
of the lantern. These spread the flux emitted from the lamp in azimuth, back onto the pavement, front gardens and
house frontages. Its effect was probably minimal however, as the 35W version didnít have this prisms.
The base of the bowl was flat and clear. Therefore the flux from the lamp was allowed to pass through
the bowl without modification. This ensured the area of road directly beneath the lantern was illuminated.
The interior of the lantern was extremely simple and included just a lamp holder, terminal block and lamp steady.
A sticker simply stating ďSimplex Lighting LimitedĒ was stuck to the underside of the canopy but there was no other
Simplex Aries: As Aquired
I purchased this lantern from fellow collector Claire Pendrous. After years of service, the canopy
was covered in lichen growth, moss and dirt Ė which was to be expected from a GRP lantern.