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: GEC Z9564
Date: Late 1960s - Late 1980s
Dimensions: Length: 1232mm, Width: 210mm, Height: 216mm
Light Distibution: Semi Cut-Off (BS 1788:1964 and CP 1004:1963)
Lamp: 180W SOX

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, and the Z 9554 (for 135W SOX) and the longer Z 9564 (for 180W SOX) appeared at the end of the decade.

These massive lanterns were designed in accordance with CP 1004:1963 and were capable of lighting Group A1 roads with a mounting height of up to 40 feet. Gradual improvements in the SOX lamp range meant that the light cast immediately below the lantern was excessive – rather than redesign the bowl with a diffuser or 'V' shaped base (as several other manufacturers did), the GEC simply painted a white stripe along the base of the bowl.

Both the Z 9554 and Z 9564 were later redesigned with a new shallower acrylic bowl which only had one refractor panel instead of the two parallel panels in the original design. The Z 9954 also appeared with a G.R.P. body (and was designated the Z 9554M) but the Z 9564 was always made with its die-cast aluminium alloy canopy.

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. It appears that the Z 9554 survived the Siemens and later Whitecroft acquisitions (where it saw out its days as the MRL 135) but the Z 9564 was quietly dropped from production.

The REVO/Relite Hyperion 135 and Hyperion 180 were extremely similar (further research is required to determine which lanterns were released first). The GEC lanterns had a gap in the refractor panels by the lampholder; the REVO/Relite lanterns had refractors panels which extended the entire length of the bowl.

The base of the bowl was painted white to obscure some of the flux emitted directly below the lantern which prevented the formation of intense pools of light beneath the columns.

facing profile This lantern originally lit the private roads of Norwich University. It was replaced in the early 2000s when the lighting scheme was replaced.

front profile The lantern was in good condition and only required minimal cleaning. Some of the white paint in the canopy and on the base of the bowl had started to peel away, so will require touching up in the future.

trailing profile No photocell was ever installed. The lantern was probably part of a group-switched scheme as it was part of a private installation.

canopy Only two small spring clips were used to secure the bowl which was surprising given the length of the lantern.

logo Unlike most GEC lanterns, the maker's logo wasn't pressed into the canopy. However, an identification sticker was stuck to the underside of the canopy and had survived many years of service.

pedestrian view This lantern was an extremely good example of the first version of this lantern. The 180W SOX lamp was mounted high in the canopy with the deep bowl accommodating two parallel refractor plates. When the lantern was redesigned, the bowl was slimmed down, and the lamp only engaged with one refractor plate on either side of the bowl. This gave these early versions of the lantern a deeper, bulky design than their slimline counterparts.

vertical The lantern was originally designed with a bowl with a flat base. This was used to simply allow light emitted beneath the lamp to simply illuminate the area directly below the lantern. However, continual improvements in the performance of low-pressure sodium lamps, particularly the SOX range, resulted in 'hot-spots' being formed beneath lanterns, spoiling the uniform appearance of the road surface. A change in the British Standards then restricted the amount of light which could be emitted in this area so manufacturers had to rethink their lantern designs. Some went to considerable expense and concocted redirective systems into their bowl designs – this is where the 'V' shaped bowls came from – but the mighty GEC simply painted the bottom of their bowls white to restrict the light. Job done!

open bowl The interior of the lantern was extremely minimal. The lengthy 180W SOX lamp was held in place by a simple lampholder and one lamp steady. 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 sticker (as required by British Standards) was stuck to the interior of the canopy. This was extremely minimal just stating the manufacturer and the catalogue number.

A monster lantern, this was the GEC's 180W lantern with semi-cut-off distribution.

As too much light was distributed immediately below the lantern, the GEC bodged the design by simply painting the bottom of the bowl white (which can be seen here). Other manufacturers put V-grooves to change the distribution, but the GEC just slapped the white paint on!

The lantern was originally installed in the grounds of Norwich University.