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: REVO Silvergold C13192/S
Date: Late 1940s - Early 1950s
Dimensions: Length: TBA, Width: TBA, Height: TBA
Light Distibution: Non Cut-Off (BSCP 1004:1952)
Lamp: 90W SOX (originally 140W SO/H)

The REVO Silvergold range was developed after the Second World War. It comprised a family of two different sized models (each of which could take two different sized low-pressure sodium lamps) which were developed for Group A or Group B use (as specified in the MOT Final Report of 1937).

Furthermore, two different versions were produced of each of these models, as they were available for either side entry or top entry mounting.

The lantern's body was made of aluminium castings, bolted onto the large canopy, with glass refractor plates mounted either side of the lamp. The bottom of the lantern was open - this allowed maximum light output but also allowed the ingress of dust and insects.

It was the first lantern in REVO's range to be called the Silvergold - this name was used for most of its successor lanterns, a quick and easy way to specify the low-pressure sodium option.

The lantern was manufactured until the early 1950s when it was replaced by a fully enclosed version.

facing profile This REVO C13192/S was rescued from Marchington Camp in the late 1990s. They were mounted on the main storage buildings and used to light the entrances and surrounding roads. Original to the camp, which was built in the early 1950s, the lanterns were now derelict, and were supplemented by additional floodlights. Many of the lanterns had pieces missing, but several were still complete, and these were rescued with the permission of the site owners.

front profile The lantern was still in relatively good condition. All the pieces were still intact and there was only minimal rusting to the enamel reflector. It simply required dismantling, a good clean, repainting and reassembling.

trailing profile This lantern was an excellent example of an open low-pressure sodium lantern with glass refractor panels. Unlike many contemporary designs from other manufacturers, which used two small refractor plates side-by-side, REVO utilised single glass refractors. These were constructed from two pieces of glass: a thick piece with horizontal prisms for light control; and a second flat plane which fitted over the prisms to keep dirt and insects away and facilitate cleaning.

canopy By modern standards, the lantern was exceptionally wide. This allowed the refractor plates to be angled inwards to the bottom of the lantern. The canopy was made from a single piece of cast aluminium alloy. The top of the lantern was not completely smooth and dropped slightly to the sides (to allow rainwater to disperse), featured several extruding lugs (to accommodate fixing bolts) and had some ribbed decorating and detailing sections. It was sprayed with yellow etching primer. The lantern was so worn when it was taken down, that most of the original paint had gone, and the original yellow etching primer was exposed. I liked this effect and simply recreated it – this is why the lantern appears light yellow.

logo The top of the lantern featured "REVO" and "Prov Pat" for "Provisional Patent." The underside of the canopy was stamped with the lantern's catalogue number and the various options for the entire family of lanterns. It was clamped to the bracket by two sets of external clamps, bolts and nuts.

pedestrian view Two aluminium endpieces were bolted to either end of the canopy which, in turn, held the refractor plates in position by means of some copper lugs. These end pieces were asymmetrical with a large bulbous piece at the pavement end which accommodated the lamp holder and its associated assembly. The road-side of the lantern simply held the refractor plates in position and had an opening to accommodate the end of the lamp.

vertical A secondary optical system included an enamel seagull reflector over the lamp. This had started to rust at the edges but was otherwise in good condition. This reflected light emitted above the lamp back down to the refractor plates and the road surface. The lantern was also open, which allowed the maximum light to light the road immediately below the lantern – a false economy as the interior of the lantern would get extremely dirty and require more cleaning.

One of the broken lanterns still in-situ at Marchington Camp. The lanterns themselves were mounted on long outreach brackets with decorated steady bar and were bolted to the frame of the building. The control gear was mounted inside the buildings in REVO cast iron boxes.

These lanterns had long fallen out of use and new floodlight had been installed below the redundant lanterns.