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 745
Date: Late 1950s - Early 1960s
Dimensions: Length: TBA, Width: TBA, Height: TBA
Light Distibution: Semi Cut-Off (BS 1788:1951)
Lamp: 140W SO/H (90W SOX)

The top of the canopy acted as the secondary optical system, being stove enamelled white to reflect further flux.

facing profile This lantern was originally sited along Cambridge Road, Milton. It was probably installed in the late 1950s or early 1960s; and survived until the Cambridgeshire-Northamptonshire PFI swept it away. I rescued it for the collection.

front profile It still had its original bowl and refractor plates. Given that these had not gone milky with age - a sign of UV exposed Perspex - then I believe this lantern was fitted with the more expensive acrylic bowl and refractors. (All of the lanterns along this stretch of road were in equally good condition but I was only able to save one).

trailing profile The only problem with the bowl was an ancient crack along the end - this can be seen in this photo. The vertical spreading effect of the refractor can also be seen - this would've fashioned the flux from the lamp into a main beam to cast down the road.

canopy It was a very clean and tidy lantern and only required a wash. The stainless steel hinges and catches had performed especially well and even retained their shine.

logo The maker's logo was cast into the lantern’s canopy – which was standard for most ELECO lanterns. The model number was also cast into the underside of the canopy: in this case is was the model number which was HW 745 1A SIDE (the "SIDE" signifying "Side Entry").

pedestrian view The extruded spigot can be clearly seen in this view. This gave the lantern a slightly "dropped" appearence when it was mounted on a bracket and viewed from the street.

vertical The bowl was held in position by a bowl ring which can be seen here. The bottom of the bowl itself was flat; a later version of the lantern had an inverted "V" cast into the base of the bowl to further distribute and diffuse the flux emitted directly below the lantern.

open bowl The interior of the lantern was rather fussy and complex with bosses and flattened extrusions. This suggested the canopy was made for a lantern which did accomodate gear but it was modified as the design evolved. The lantern included a cable clamp, earthing screw, porcelain terminal block, lampholder assembly and lamp steady. The lamp steady was angled so, when turned 180°, could engage with a smaller length lamp. The extruded threaded hole for the lamp steady was marked "POS1"; the two flattened circular areas next to it were labeled "POS2" and "POS3" - this allowed for difficult lamp lenghts until someone came up with the idea of the angled lamp steady. The four corners of the underside of the canopy had extruded screw holes to allow a reflecting plate to be installed, and which formed a secondary optical system. This wasn't fitted in this example.

This example was probably installed in the 1960s and remained standing and unaltered (with the exception of a photocell) until 2016 when it was removed as part of the Cambridgeshire-Northamptonshire PFI. It was then rescued and added to the collection. The only blemish was a slight crack in the bowl - not bad for over 60 years of service.