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: ELECO HW 505
Date: Late 1950s - Early 1960s
Dimensions: Length: 20¼", Width: 11 3/8", Height: 8½"
Light Distibution: Semi Cut-Off (BS 1788:1951)
Lamp: 35W SOX

This lantern was one of the earlier 1950s examples, a huge lantern by later standards. It was primarily designed around the dimensions of the enormous old leak-transformers and capacitors so the canopy was made wide enough to accommodate them. The size of the gear meant the lamp-holder, lamp-steady and lamp were positioned low, necessitating a large Perspex bowl to accommodate everything.

Unfortunately, little is known about this lantern as no documentation has surfaced. It probably appeared in the late 1940s/early 1950s, the first of the firm's aluminium and Perspex lanterns, replacing their old cast-iron and glass refractor lanterns which were their standard design before that.

It was probably the largest lantern ever made for the 45W-60W (later 35W) low-pressure sodium lamp.

The top of the canopy acted as the secondary optical system, being stove enamelled white to reflect further flux. If gear was not fitted, a large stainless steel plate was installed in the canopy, providing a flat reflecting surface.

facing profile This ELECO HW 505 was originally installed somewhere in the Burton area and was obtained from another collector.

front profile This shot shows how wide this lantern is - its dimensions are closer to a 90W low-pressure sodium lantern. This was to accommodate the huge old leak transformers and capacitors of the late 1940s/early 1950s. The bowl was original and made of Perspex. This has started to go milky and opaque over the years but would've originally been transparent.

trailing profile The bowl was also slightly asymmetric with a tapering end at the road side and a vertical end on the pavement side. This gave the lantern a characteristic appearance, a detail lacking in most other smaller wattage low-pressure sodium lanterns. The bowl also had maker and model number cast into the rim. In this case, the text read 'ELECO LTD. ST. ALBANS. HW 505/2.'

canopy The top of the canopy was gently curving with a large lip around its perimeter. This flattened lip engaged with the bowl ring underneath. This was also the earliest ELECO lantern to feature the characteristic twin hinges and single stainless-steel toggle clip on either side of the lantern.

logo The lantern's canopy was completely smooth. The firms logo was not cast into the canopy which would be a feature of their later lanterns. This was one of the first lanterns to feature ELECO's classic arrangement of two hinges and one stainless steel bowl clip on opposite sides of the lantern.

pedestrian view The glue holding the refractor plates in position had reacted with the Perpsex bowl over the years, degrading the plastic and causing it to become brittle and porous. This allowed the ingress of dirt and algae. Attempting to rigorously remove and clean this dirt would probably break the bowl, given its fragile condition.

vertical The view from beneath the lantern showed just how wide the base was. The bowl was clear here as the flux would've naturally been spread by just the lamp and no redirection was required. (Note: The lantern has been mounted the 'wrong-way around' in this shot - the lampholder should be positioned pavement side where the bracket is).

open bowl This shot shows how the bowl was mounted in an aluminium bowl-ring. This was a standard design shared by many manufacturers before they created bowls with oversized edges which engaged the clips so a bowl ring was not required. The stainless steel over-reflector can clearly been seen. Note that the lamp steady had to be bolted through the over-reflector rather than screwing directly into the canopy. The original asbetos wiring can also be seen in this shot. (Note: The lantern has been mounted the 'wrong-way around' in this shot - the lampholder should be positioned pavement side where the bracket is).

restoration The restoration procedure for this lantern was to respray the interior of the lantern, ensure all the screws were greased and to retain as many original features as possible. It is one I intend to return to at some point (the felt gasket needs replacing and the rusted screws on the lampholder need changing). The original cable clamp, terminal block, earthing screw, lampholder assembly and wiring has been kept. The lantern's manufacturer and identification were cast into the underside of the canopy and state "E L E C O ST ALBANS" and "HW 505/1B". The various lugs and screw holds for the optional gear can also been seen.