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: Simplex Aries
Date: Early 1970s - Late 1980s
Dimensions: Length: 54.5cm, Width: 18.4cm, Height: 17.2cm
Light Distibution: Semi Cut-Off (BS 4533)
Lamp: 35-55W SOX

The vertical refractors at the pavement side of the lantern were designed to spread the light in azimuth. This would’ve spread the light back onto pavements. (The smaller 35W version of the lantern omitted this part of the refractor design).

The lantern didn’t have an overhead reflector. The glass reinforced plastic of the canopy was white anyway so it could reflect back any light emitted above the lamp.

There was no spreading refractor in the base of the bowl. The narrow flat base simply allowed the light from the lamp to illuminate the area directly beneath the lantern.

facing profile I purchased this lantern from fellow collector Claire Pendrous. The original installation location of the lantern was unknown, but it had been in service for many years, and was relatively dirty and unmaintained. The only restoration required was a strip down, thorough cleaning, and reassembly.

front profile Even though it was the larger 55W version, the lantern appeared extremely small and sleek. It had a very compact design and it’s hard to believe that gear could be accommodated as an option as well.

trailing profile Despite years in service, the lantern was still in good condition. After a good cleaning, the only indication of the lantern’s long service life was its yellowing polycarbonate bowl.

canopy The bowl was hinged on the traffic facing side of the lantern with the toggle clips on the other.

logo The canopy was flat and unadorned with maker’s name or logos. A large extruded cylindrical area provided a convenient mounting place for an optional photoelectric cell.

pedestrian view As this was the larger 55W version, the bowl included the characteristic vertical grooves at the pavement side of the lantern. These spread the flux emitted from the lamp in azimuth, back onto the pavement, front gardens and house frontages. Its effect was probably minimal however, as the 35W version didn’t have this prisms.

vertical The base of the bowl was flat and clear. Therefore the flux from the lamp was allowed to pass through the bowl without modification. This ensured the area of road directly beneath the lantern was illuminated.

interior #1 The interior of the lantern was extremely simple and included just a lamp holder, terminal block and lamp steady. A sticker simply stating “Simplex Lighting Limited” was stuck to the underside of the canopy but there was no other identification.

I purchased this lantern from fellow collector Claire Pendrous. After years of service, the canopy was covered in lichen growth, moss and dirt – which was to be expected from a GRP lantern.