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gec z9565

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: GEC Z9565
Date: Late 1960s - Late 1980s
Dimensions: Length: 1314mm, Width: 318mm, Height: 143mm
Light Distibution: Cut-Off (BS 1788:1964 and CP 1004:1963)
Lamp: 180W SOX


The 1960s saw constant upheaval and change in the lighting industry as several new lamp types were developed, necessitating the design of ranges of new lanterns. One of the most frenzied areas of redevelopment was for low-pressure sodium lamps, with the introduction of the SLI/H range in the early 1960s and the unveiling of SOX in the late 1960s.

Developments of SOX included the debut of the 135W and 180W sizes which required new, much larger lanterns. Some manufacturers simply adopted existing SLI/H designs, elongating the bowls to accommodate the larger diameter SOX tubes, but the GEC took the decision to design an entirely new range. Interestingly the firm created a new range of lanterns which included a 90W SOX version. The Z 9545 90W SOX), Z 9555 (135W SOX) and Z 9565 (180W SOX) all had the same boxy apperance and appeared in the late 1960s.

This family of lanterns was designed in accordance with CP 1004:1963 and were capable of lighting Group A1 roads with a mounting height of up to 40 feet. With an eye for lighting motorways, the GEC also produced a gear-in-head version, which accommodated the gear in a large shoe at the spigot end of the lantern. This range, the Z 9543, Z 9553 and Z 9563 was considerably rarer as many lighting authorities picked competing products by Philips and Thorn to light motorways.

Both lanterns remained on the GEC's catalogue for years, up until the company sold its lamps and lighting division to Siemens in the early 1990s.


The Z 9565 quickly found a niche lighting roundabouts, complex junctions and dual carriageways. The cut-off distribution was preferred for roundabouts and junctions where the number and direction of lanterns could be confusing visually if semi-cut-off was used. As a cut-off, it could also be used for lighting major roads near the vicinity of railways and airports where light spill was carefully controlled.


This boxy lantern was very easily identified but its angular, square shape.

Optical System

The optical system was the classic 'cross-over' cut-off distribution which was developed back in the 1930s. Two brightened and anodised reflectors formed the main beams which were positioned on either sides of the lantern. The sides of the lantern were opaque so light emitted above 75° was cut-off. The acrylic bowl was flat and really just enclosed the lantern, keeping dust, dirt and insects out of the luminaire.


The Z 9545, Z 9555 and Z 9565 were gearless lanterns. The GEC produced another range - the Z 9543, Z 9553 and Z 9563 - which included gear shoes.

the gec z 9565 in my collection

facing profile

This lantern was originaly installed on The Keyway, Willenhall, West Midlands.

This side profile shows how sleek and minimal the lantern is - it is really just an aluminium box with a flat profile acrylic bowl with a spigot assembly bolted onto one side.

front profile

The lantern was in good condition and only required minimal cleaning.

The acrylic bowl was still in good condition and was held in place by three hinges and three toggle catches.

trailing profile

The lantern was fitted with a single photocell. This may have been a factory addition given that the wiring in the lantern explicitly supported the provision of a photocell.


The spigot assembly was not integral to the pressed canopy of the lantern. After the pressing, folding and riviting of the thin aluminium alloy into a lengthy box, the spigot assembly was bolted onto the end of the lantern.


Unlike most GEC lanterns, the maker's logo wasn't pressed into the canopy. However, a metal identification plate was fitted inside the ribbing inside the lantern. Internal structures inside the lantern - such as extra strengthening ribbing and lamp steady, were rivited to the canopy.

pedestrian view

The lantern's design remained remarkably constant over its lifespan. As a simplistic cut-off design, there was little scope for fundamentally changing its design.


The lamp was mounted centrally within the lantern. A single lamp steady supported the large 180W SOX lamp at one end whilst the lamp assembly supported the other. The grub screws to lock the spigot into the spigot assembly were mounted on the underside - an attempt to prevent corrosion and seizing.

open bowl

The bowl sat snuggly in a trough around the perimeter of the lantern which was fitted with a felt gasket.

Two polished steel reflectors were rivited to the sides of the canopy, redirecting the light into two beams, which were directed onto the road surface. The wide flat bowl also allowed a large amount of flux to illuminate the area directly beneath the lantern. In addition to the lampholder were two terminal blocks (one for the lamp, one for an optional photocell), earthing screw and cable clamp.

The underside of the canopy was painted white to act as a secondary optical system, reflecting the light emitted above the lamp back down through the lantern, and onto the road surface.

interior #1

An identification plate(as required by British Standards) was rivited to one of the strengthening ribs on the interior of the lantern. This was extremely minimal just stating the manufacturer and the catalogue number.

The two terminal blocks, each with a separate cable clamp, can be clearly seen in this shot.

gec z9565: as aquired

The final cut-off sodium lantern produced by the GEC, the lantern was also the simplest of cut-off design, being just a light-weight box with reflectors mounted on either side of the bulb. Simple, but probably one of the best looking specialised cut-off lanterns ever produced.

This monster was the largest of the range taking 180W SOX.

The lantern was originally installed on The Keyway, Willenhall, West Midlands and was obtained as a swap with Claire Pendrous.