revo silvergold c13192/s
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: 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)
REVO was one of the dominant street lighting manufacturers of the post-war period. From their
manufacturing base in Tipton, their columns, brackets and lanterns were installed in quantity throughout the UK as well as the world.
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
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.
The lantern was not popular, probably due to its short lifespan. The successor models were far more popular, suggesting that
this lantern was only available before the post-war rebuilding and relighting really got going.
Early metal framed open sodium lanterns are quite difficult to identify thanks to their novelty and mostly identical construction.
They often comprise large cast canopies to which the end pieces are bolted and identical plate glass refractors. The REVO
example can be identified by its singe piece plate refractors (other manufacturers used two smaller Holophane plate refractors
side-by-side) and the opening on the road side of lantern through which the lamp's end can be seen.
The primary optical system is designed to cast a non-cut-off non-axial asymmetric distribution in accordance with the MOT Report 1937/BSCP 1004:1952.
The two large glass refractor plates mounted on either side of the lamp perform this function. A secondary
optical system comprises a curved "sea-gull" white-enamelled over-reflector which
redirects flux emitted above the lamp back to the street surface.
The lantern had no capacity for gear. This was mounted remotely.
The REVO Silvergold C13192/S In My Collection
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.
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.
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.
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 Ė this is why the lantern appears light yellow.
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.
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.
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 Ė a false
economy as the interior of the lantern would get extremely dirty and require more cleaning.
The REVO Silvergold C13192/S As Aquired
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.