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: Whitecroft SRL35A
Date: Late 1980s - Late 2000s
Dimensions: Length: TBA, Width: TBA, Height: TBA
Light Distibution: Semi Cut-Off (BS 4533:1976)
Lamp: 35W SOX

As successful and popular lanterns, there was probably little impetus to change them, but by the 1980s, the GEC introduced the Z9582, a super-slimline lantern for 35W SOX, equipped with gear, and almost half the height of its 1960s ancestor.

This lantern was probably the last designed by the GEC. A succession of internal shuffling (which saw the entire street lighting range transferred to the Osram arm of the company) before two sales of the manufacturing business saw the lantern subsequently produced by four separate companies.

Both GEC, Osram and Siemens (who purchased the street lighting business) retained the lantern’s distinctive GEC catalogue description. When the dwindling range was then purchased by Whitecroft, the lantern was rechristened the SRL 35 (Side Road Lantern) where it remained almost unchanged in the product catalogues for over another ten years.

The underside of the gear tray is painted white and acts as a secondary reflector.

The exterior of the bowl is smooth to facilitate easy cleaning.

facing profile This lantern saw service somewhere in the Brighton area. I don’t know where it was originally installed.

front profile The lantern was in good condition and only required minimal cleaning to freshen it up. A little interior rusting of the gear tray was the only indication of a life in service.

trailing profile The photocell appeared to be original to the lantern and not a later addition whilst in service.

canopy The bowl was still transparent and unclear, suggesting it was made from acrylic.

logo There were no identifying marks on the canopy of the lantern. The only writing was a "Disconnect Supply" warning for potentially careless lighting engineers.

pedestrian view The side refractors produced the main beam and were held in a "V" shape against the side of the bulb. This was a characteristic GEC design which was more pronounced in earlier generation lanterns (such as the Z9530 and Z9480 ranges).

vertical The base of the bowl was also wider than the lantern’s ancestors. These refractor prisms were used to spread the light beneath the lantern, so bright spots wouldn’t form on the road surface under each street light. The bowl still bore its GEC classification: Z6880. None of the companies who manufactured the lantern in turn saw any point in changing the moulds. The bowl also shared a design characteristic only seen in another GEC lantern. The rubber gasket was integral to the bowl rather than glued to the canopy; a design also seen in the GEC Z9494 range.

open bowl The interior of the lantern clearly shows the underside of the gear tray which acts as a secondary reflector.

interior #1 The removal of the gear tray clearly shows the interior of the lantern. The gear is mounted on the underside of the gear tray (the other side is painted white and acts as a secondary reflector). A Whitecroft ballast (SZ355K245), Cambridge Capacitors capacitor (8uF) and Whitecroft Ignitor (ISX36-P) are fitted. The interior of the canopy is standard with grub screws, earth mounting screw, cable clamp and terminal strip. Like with the bowl, the original manufacturing moulds were never changed, and the lantern retains its original GEC part number of ZD7027/A. A Whitecroft sticker in the canopy clearly determines its maker. (This could’ve also been deduced from the gear however).

This lantern was originally installed somewhere in the Brighton area.