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: Siemens Ediswan Orson Lantern
Date: Late 1950s - Early 1960s
Dimensions: Length: TBA, Width: TBA, Height: TBA
Light Distibution: Non Cut-Off (BSCP 1004 Part Two:1956)
Lamp: 85W SO/H (55W SOX)

facing profile This lantern was installed on an approach road to a timber factor near Inverness in 1961. It was one of an installation of twenty-five Orson lanterns and one Oline lantern; the use of timber columns for the lanterns was of sufficient interest for Public Lighting to write about it.

front profile The front profile clearly shows how enormous this lantern is. The deep bowl dwarfs the relatively slimline canopy. The dark area in the canopy is the space for the huge 1950s control gear, hidden underneath a separate over-reflector.

trailing profile The bowl has been damaged during its years of service. It appears to have been used for target practise by the local youths when the factory area became derelict. Over the years, the refractor plates became unglued and were lying in the base of the bowl, which is why they escaped damage.

canopy The canopy was smooth and featureless. There were no side clips either; the bowl being secured by two large hinges on the path-side of the lantern, and a knurled screw at the other end.

logo There were no makers marks or logos cast into the top of the canopy. This made initial identification difficult.

pedestrian view There is a large hole in the path-side portion of the bowl but due to the rarity of this lantern (only three were saved) then this damaged bowl will have to be retained. The only optical control is via the two refractor plates which are glued onto each side of the bowl.

vertical This shot again shows how large the lantern is. The 55W SOX bowl appears lost inside; the width of the canopy being dictated by the dimensions of the original huge leak transformer.

interior #1 The interior of the canopy is very basic and rigid. There are mounting points for the leak transformer, power correction capacitor, lamp holder assembly and over-reflector.

interior #2 A number "1832" and the hexagonal logo "ADC" are cast into the interior of the canopy but it isn’t known what these refer to.

interior #3 This shot shows the open-coil leak transformer and power correction capacitor installed. The asbestos wiring has been replaced. The power correction capacitor was clearly manufactured by Siemens Ediswan as the oval logo can be seen but the manufacturer of the leak transformer isn’t known. There was an oval mark where a sticker was once placed, and its shape suggests Siemens Ediswan made the leak transformer as well. Older gear tends to work extremely well and the gear lit a new 55W SOX lamp after over fifty years of service.

interior #4 The final shot shows the interior of the lantern with the over-reflector in place. This thin white-painted piece of steel also carries the lamp steady.

A small installation of these lanterns was spotted by John Mitchell. They used to light the approach road to factory which was now derelict. Interestingly, the columns were made of wood, with metal brackets supporting the lanterns.

John arranged the removal of three lanterns with the demolition firm in 2009. Amazingly one was still fitted with an 85W Siemens Ediswan SO/H bulb. Unfortunately all three examples had limited bowl damage but this was acceptable given the rarity of the lanterns. John kept one for himself and the other two were sold to collectors.

Identification of the lanterns was difficult. There was no maker's mark, no identification stickers and a small logo and number cast into the canopy simply confused matters further. The gear (original open-wound leak transformer and capacator) had dark areas where the manufacturer's stickers were, and their oval shape suggested Siemens Ediswan.

The only lantern which fitted the description was the Orson but I didn't have any pictures.

Amazingly, whilst looking through Public Lighting, I found a piece written about their installation. Not only did this finally identify the lanterns, but it gave their installation date of 1961.