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: Wardle Liverpool
Date: 1934 - Early 1950s
Dimensions: Length: TBA, Width: TBA, Height: TBA
Light Distibution: Cut-Off (Pre Specifications)
Lamp: 140 SO/H

facing profile This lantern was originally installed in the West Derby suburb of Liverpool. It was removed in the 2000s and acquired by fellow collector Colin Jackson who gave it to me. After over 50 years of service, the lantern was in dreadful condition and was little more than a shell.

front profile It has been fully restored and painted a dark green. In this shot, the two wing nuts which positioned the mirrors for either 20’ or 25’ mounting height can clearly be seen.

trailing profile The lantern had a substantial aluminium top canopy to which was bolted two frame end-pieces. Onto these were screwed two identical end-caps – so both had lampholder extrusions although only one was occupied – and the two opaque curved thin aluminium side pieces.

canopy The two frame end-pieces were held in place by substantial bolts which screwed through the top of the canopy. The mounting conduit had a tiny diameter and necessitated an adaptor T-piece to allow it to be screwed onto standard diameter brackets.

logo No logo or identification was found on the lantern. The top of the canopy was entirely smooth. However, they were never there and had not corroded away, as various part numbers could be found on the components which made up the lantern.

pedestrian view The base of the lamp can just be seen in this shot. The mirrors were held in curved slotted brass mounts that pivoted by a screw at the top and could be moved slightly by the wing nuts at either end of the lantern.

vertical The whole interior of the lantern was painted white to act as a secondary optical system. The main beams were fashioned by the curved mirrors which were positioned on either side of the lamp. The interior was also extremely basic as there was just one mounting point for a terminal block.

gear box One of the gear boxes was also rescued and this was completely restored. It contained a large leak transformer, square condenser and two fuses. These were all extremely rusted and degraded. Therefore, the restoration here was just to clean everything up, repaint the box and add a new sticker to the leak transformer.

They had been painted grey and were in dreadful condition after being in service for 50 years. They were battered and bent, there were holes in the side panels, the mirrors were long gone, the lamp steady was falling to pieces and all the wiring was hard and brittle.

The best pieces from both lanterns and gear boxes were used to make a complete example. This was then restored.