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: Relite Hyperion 135 A42.401
Date: Early 1970s - Mid 1970s
Dimensions: Length: 35", Width: 8", Height: 8"
Light Distibution: Semi Cut-Off (BSCP 1004 Part One and Two:1963), BS 1788:1964
Lamp: 135W SOX

History The Relite Hyperion was the third, and final version, of the popular Hyperion lanterns first made by REVO. This lantern was a complete departure and redesign from its REVO forebears and had no resemblance to the early lanterns. Two versions were designed for 135W and 180W SOX respectively and both featured the same aluminium-alloy canopy and slim Perspex bowl. The lantern was extremely compact as it was designed exclusively for the SOX lamp and not the slightly longer SLI version. Adverts for the lantern first appeared in 1972 where the lantern was described as new. However, it isn't known if Simplex continued to manufacture the lantern when it took over Relite in 1975, so the lantern may have only had a short manufacturing run. Popularity Despite its relatively short manufacturing run, the Hyperion 135 and Hyperion 180 were relatively popular lanterns and were installed in large numbers by various authorities around the country. Identification Identification can be tricky as the lantern is very similar to the GEC Z9554 and Z9564 lanterns. The bowl in profile is slightly slimmer on the Hyperions, but the real difference is the refractor panels which are fitted along the entire length of the bowl on the Hyperions. Optical System The semi-cut-off light distribution is provided by the two refractor panels the length of the bowl. The interior was also painted white to redirect flux emitted directly above the lamp within the canopy of the lantern. Gear The gear was too big to mount in the lantern and so had to be provided remotely.

facing profile This lantern came from Newmarket Road, Cambridge. It was probably installed in the mid 1970s so saw over forty years of service. It was not a popular lantern in Cambridge was was used as casual replacements in a couple of places in the city. A small number of these lanterns lit the section of Newmarket Road where it passed over the railway line near the football ground. My thanks to Cambridge County Council and Balfour Beatty for saving this lantern for me.

front profile The lantern was extremely compact with the bowl being just wide and deep enough to surround the large 135W SOX lamp.

trailing profile Each side of the bowl was fitted with two refractor plates. These filled the entire profile of the bowl (unlike the GEC Z9554 which had no refractors near the lamp holder). The design of the refractors is unique. A normal plate refractor is stuck along the length of the bowl but there's also a second refractor (which is only one thick prism) stuck below it.

canopy The lantern used four stainless steel clips to secure the bowl as opposed to the end bowl clips used by the earlier versions of the lantern.

canopy There was no manufacturers’ mark or name on the smooth, slim canopy of the lantern.

pedestrian view The lamp could be accessed by undoing two clips on the side of the lantern with the bowl swinging to the side on two hinges. This had almost become an industry standard by the early 1970s.

pedestrian view The base of the bowl was flat unlike the previous Hyperion B model. This was due to a relaxing of the specification which had been considered too rigid. Interestingly there was also an extra sheet of plastic stuck to the base of the bowl inside the lantern.

vertical The canopy was painted white to reflect any flux emitted above the lamp.

interior #1 The lamp was held in the lantern by the lampholder and a separate hook near the road-side. Two stickers were also stuck near the road-side of the lantern which gave the manufacturer name, a handwritten catalogue number (although this was printed on some other examples) and the BSI Kite Mark.

interior #2 The electrical connections were minimal and included a terminal block for incoming power supply and a separate terminal block for the photocell. The lantern was secured to the bracket by four grub screws – a departure from the clamps used in earlier Hyperions.