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: Phosco P153 (Third Version)
Date: Late 1950s - Late 1960s
Dimensions: Length: TBA, Width: TBA, Height: TBA
Light Distibution: Non Cut-Off (BSCP 1004 Part Two:1956)
Lamp: 35W SOX

By the mid 1950s, the rebuilding of the UK’s infrastructure was proceeding at full speed, and many new companies appeared who were eager to pick up the various lucrative relighting contracts. Phosware (later Phosco) were founded by Concrete Utilities; the firm were experiencing unprecedented demands for their concrete columns (as the use of steel for street lighting was still restricted) and decided to branch out into lantern manufacturimg as well. Their first low-pressure sodium lanterns were simple open-types, but the firm soon developed a family of enclosed low-pressure sodium lanterns. This family were typified by their aluminium canopies, wide and deep Perspex bowls (designed to accommodate the huge bulky gear of the era), vertical refractor grooves at the end of the bowls, and overhanging lip which accommodated the "Oddie Key" (a unique bowl fastening mechanism only used by Phosco). The P152 series replaced the firm's first range of enclosed gear-in-head lanterns (which was the P120 series). These were huge by modern standards, and the P152 series was slightly smaller, reflecting the smaller sized control gear being fitted inside the lanterns. The P152 supported top-entry whilst the P153 was designed for side entry. The P153 was one of the smallest lanterns in the range, designed for the early 45-60W SOX lamps. During its lifetime, the lantern was modified, yielding a series of slightly different canopies, bowl styles and bowl locking mechanism. The first version of the lantern was of similar construction and styling to its direct ancestor, the P120 range. The canopy was smooth and the bowl was secured by the familiar "Oddie" key. The second version remodelled the canopy by making it flatter and incorporating a bulge in the centre where the gear was housed. The third version employed the modified canopy and replaced the "Oddie" key mechanism by a bowl ring and a new fastener. All of these versions took a similar style bowl. Whilst the dimensions of the bowls were the same, and all sported the distinctive vertical grooves, some featured refractor plates with widely spaced refractor prisms whilst others used narrower spacings. These lanterns were the staple Phosco product for Group-B low pressure sodium lighting until they were replaced in turn by the even sleeker P223 range in the late 1960s.

The vertical refractors at the end of the lantern are designed to spread the flux in azimuth.

The interior of the canopy is also painted white, but this secondary optical system only reflects a fraction of the flux as most is reflected by the overhead reflector.

facing profile I've never seen this lantern in an installation although I understand they were popular in Edinburgh and Manchester. (The old-style version of the lantern appeared to be much more common; and there are still sizeable installations in Hertfordshire).

front profile This shot clearly shows the vertical refractor grooves at the end of the lantern. This was a PhosWare standard design for all their early lanterns. It was designed to spread the flux in azimuth, spreading the small amount of light emitted from the ends of the bulb.

trailing profile Despite years in service, the lantern was still in good condition. The bowl was still clear; the interior required some repainting and the canopy was painted light-blue. I obtained the lantern from fellow collector Colin Jackson and I understand he'd kept this lantern inside for a number of years.

canopy The profile of the lantern dipped around the edges giving the central area of the canopy a pronounced "bulge." This provided space for the control gear, but also allowed for a slightly smaller sized lantern.

logo There were no maker’s marks or logos on the top of the canopy. And unlike the earlier P120 range, the lantern's name wasn't embossed on any parts of the lantern. Phosco also used silver stickers on the interior of the lanterns. These gave the manufacturer's name, model name and voltage requirements. Unfortunately, if this lantern ever had a sticker, it had long gone.

pedestrian view The three key areas of the refractor bowl can be seen in this shot: the vertical grooves at the bowl ends to spread the light emitted; the main refractor panels which fashioned the two main beams; and the frosted base which acted as a diffuser and scattered the light emitted below the lantern.

vertical This shot shows the metal bowl ring and metal catch required to hold the bowl in place. However, the bowl was exactly the same as the ones fitted to the old P153 lantern, and even included a hole for an "Oddie" key.

interior #1 The interior of the lantern was extremely simple with two screw holes for the bulb assembly, two screw holes for the two securing Allen keys and two screw holds for the gear support chassis and over reflector assembly. The design was changed from the earlier version of the lantern by the central dipped area (which allowed for the control gear and gave the canopy its distictive profile) and the provision of a bowl ring and hinge.

interior #2 The gear chassis originally took a medium sized sodium ballast (a Thorn AME 53182 for 35W and 55W sodium lamps) and a cylindrical capacitor (a Hunts Z8203A rated at 13uF). I beleive these to be original to the lantern.

interior #3 This shot shows the metal chassis in place. The ballast and capacitor are mounted back-to-back (in the same manner as in the earlier P120 range) but the frame is much simpler and simply bolts to the chassis at either end of the lantern.

interior #4 The over-reflector is then mounted over the gear and secured to the canopy by four screws. It is simply a reflective device; it doesn't double-up as a gear-tray as in other lanterns. The lantern has been installed on a Wall Bracket.

I purchased this lantern from fellow collector Colin Jackson. It was originally installed in the Manchester area.