Urbis ZX 1
Genre: Enclosed Horizontal Traverse High Pressure Sodium Lantern
As soon as the low pressure sodium lamp (LPS) was developed, the race was on to develop a version which would run at high pressure (HPS).
The research was stimulated by the prospect of the spectral broadening of the light emitted from such a bulb and
the improved colour rendering which would result. However the development was hampered by the lack of a translucent material which
could withstand the chemical attack of sodium vapour at extremely high temperatures and pressures.
It wasnít until the early 1960s that General Electric (GE) cracked the problems,
closely followed by the GEC and Philips. A prototype high pressure sodium lamp was
exhibited at the APLE's annual conference in 1963, but it wasnít until 1966 that the GEC erected an experimental installation
along East Lane, Wembley (which, incidentally, also saw the first experimental medium-pressure mercury installation over thirty years before).
The first commercial installation in the UK was erected along the Southend ring road, but it was the City Of London who gained the most
recognition by beginning a radial upgrading of all their lighting to high pressure sodium in 1967. As the early HPS bulbs were designed
to be retrofitted into existing mercury installations, the lanterns chosen by the City Of London were slightly modified versions of
existing mercury lanterns.
The first true HPS lanterns (designed from scratch with the new light source in mind) appeared in the late 1960s and early 1970s. All
these lanterns utilised a cross-over design: whilst this was an adaption of existing mercury lanterns, it also moved the lamp up into
the lanternís canopy (where it could not be directly viewed by drivers, thus minimalising the glare) and allowed designs to cater for
both cut-off and semi-cut-off.
Wider adoption of high pressure sodium was stalled by the energy crisis, as it couldnít match the efficiency of its low pressure sodium brother.
Councils, believing in the simple maximum lumens per watt paradigm, replaced existing tungsten, mercury and fluorescent schemes by
low pressure sodium. So it wasnít until the 1990s that HPS started appearing in greater quantities.
With its efficiency between high pressure mercury and low pressure sodium, HPS became even more attractive when LPS was finally exorcised
from the British Standards of street lighting (as it didn't provide an adequate colour rendering). However, it didn't remain as first choice for
new and replacement lighting schemes for long. Renewed interest in fluorescent (from compact fluorescent sources), the emergence of affordable
metal halide and the possible introduction of LED have all questioned the automatic selection of high pressure sodium for schemes.
Therefore by the end of the first decade of the new century, high pressure sodiumís position as the natural choice for street lighting
was coming under pressure.
Name: Urbis ZX 1
Date: Circa Early 1980s - Mid 2000s
Dimensions: Length: 635mm, Width: 290mm, Height: 147mm (flat glass protector)
Light Distibution: SealSafe 1200, 1543, 1317 system. Conforms with BS 5489-1 / EN 13201.
Lamp: 50W, 70W, 100W SON
Itís probably not inaccurate to state that Urbis came to prominence with this lantern. It embodied
the philosophy of the company; to produce a rugged, well built and aesthetic luminaire combined with the companyís
drive towards totally sealed products. This led to their development of the SealSafe optical systems.
The lantern was first used to light the side-streets of Wandsworth in 1980. It was an extremely successful installation
and gave both the company and the lantern prominence. A SealSafe version of the lantern was developed in
1985, and the lantern became the companyís flagship lantern for side-street lighting for the next twenty years.
After a version with universal mounting was developed (called the ZXU1) in the 2000s, the lantern had another few
years of life, before being replaced in the catalogues by the Opalo in the mid 2000s.
The lantern was moderately popular, becoming the side-street HPS lantern of choice for many authorities. It had stiff
competition from all the other major manufacturers, and their options were probably cheaper, which is probably why
the lantern wasnít taken up in greater numbers.
It was also the lantern of choice for many railway companies, and many platforms were lit by Urbis ZX1s
with modified optics, after fluorescent or tungsten lanterns were removed.
The lantern is extremely easy to identify thanks to its slim-line long two-coloured body (often grey and dark grey),
redundant clip mounts (a vestigial feature which survived a surprisingly long time), embossed grid formation on the
underside of the gear tray (an Urbis design feature) and knurled thumb screws.
The only feature that changed was the optical system. (See below).
Various optical systems were developed for the lantern, ranging from different reflector profiles, through to different
SealSafe optics combined with flat, dished or refractor bowl options. The refractor bowl was especially
interesting as it didnít feature the featureless profiles used by other manufacturers, but resembled the intricate refractor
bowl designs of the previous generation of HPMV lanterns which proceeded it.
The most common options were the:
- Reflector type 1200 (asymmetric) with flat glass, dished polycarbonate or deep-bowl refractor.
- Reflector type 1543 (asymmetric) with flat glass, dished polycarbonate or deep-bowl refractor.
- Reflector type 1317 (asymmetric) with deep-bowl refractor.
The Urbis ZX 1 In My Collection
I obtained this lantern from another collector. I believe it was originally installed on a railway platform.
It was in good condition, given that it had been used, and the label inside the lantern suggested it had been made in 1991.
Its full designation, also printed inside the lantern on a slip of paper, was ZX1/NBC/70T/1211/FG. This
lengthy code fully specified the lantern as a ZX1 which took a 70W tubular SON lamp and was fitted with the
1211 optic with flat glass.
It was coloured the standard "two-tone" grey which was the factory default. The canopy, which lifted off
entirely after undoing the two knurled thumb screws, was dark grey whilst the main lantern body was light grey.
The four extruded "lugs" on either side of the lantern were originally designed for clips to hold the
two halves together. This early design was discontinued Ė and replaced by the knurled thumb screws Ė but Urbis
continued to manufacture the lanterns with these obsolete additions. They were removed on later versions of the lantern.
The canopy of the lantern was smooth with no logo or identifying features. Provision was made for the mounting
position for a NEMA photocell, but this hadnít been installed. (Therefore the lantern was either individually or group
switched, which would be the case for one installed on a railway platform).
The base of the gear tray featured an embossed grid pattern. This was a standard design motif of this family of
lanterns and could be found on the ZX2 and ZX3.
This vertical view of the lantern reveals the 1211 reflector optic which can
clearly be seen through the flat-glass bowl.
The interior of the lantern could be clearly seen once the upper cover had been removed.
This lantern wasnít fitted with the SealSafe optic and instead mounted the lamp within the main lantern body where
it engaged with the reflector which was fitted in the upper cover. This mean that the lamp housing was subject to the
same dust ingress as the main lantern body.
All the gear was mounted on the gear tray towards the back of the lantern. The main magnetic gear was an
Urbis HSG 072 for 70W SON lamps. Alongside this was a 8uF power correction capacitor manufactured by
Cambridge Capacitors and an Urbis B070 50-70W SON starter. Each piece of gear had
the year marked, which ranged from 1990 to 1991.
A printed paper slip enclosed in a plastic wallet was stick to the spigot entry. This fully identified the lantern, its
batch number (91018) and the number produced in the batch (342 of 500). This also confirmed the date of the 19th week of 1991.
Urbis ZX 1 - As Aquired
The smallest of Urbis' current range, the ZX1 is one of their Group B lanterns offering SON and metal halide
This version has the flat bowl. Other options include curved bowls or a prismatic bowl.
The original location of the lantern is unknown, being obtained by swapping with another collector.