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: REVO Hyperion A
Date: Late 1950s - Early 1960s
Dimensions: Length: 40", Width: 9", Height: 8"
Light Distibution: Semi Cut-Off (BSCP 1004 Part One:1952)
Lamp: 135W SOX (originally 200W SLI/H)

History The REVO Hyperion A was the first SLI lantern developed by REVO in the late 1950s/early 1960s. Like many of the new SLI lanterns appearing on the market, it featured a long extruded canopy, perspex bowl with refractor plates and no option for gear. (Which, at the time, was too big and bulky to put in the lantern's body.) By 1963 the model had been modified to take the newly introduced 200W and 300W SOI/H lamps. This required the removal of the second lamp connection at the street-end of the lantern. The lantern was again modified when 150W SOX became available. The 150W SOX lamp (later re-rated to the 135W SOX lamp) was slightly shorter than the original 200W SLI/H the lantern was designed for and so didn’t illuminate the whole of the refractor panels. The lantern was partially redesigned after the publication of BS 1788:1964 and reappeared in modified form as the REVO Hyperion B. Popularity The lantern was extremely popular and could be found installed throughout the UK. It was also used in many column manufacturers' adverts in the 1960s. Identification The lantern is easily identified by its elongated profile, unique bowl catch at the street-end of the lantern, and characteristic "bulge" of the bowl profile near the lamp holders. Optical System The semi-cut-off light distribution is provided by the two refractor panels the length of the bowl. The interior was also painted white to redirect flux emitted directly above the lamp within the canopy of the lantern. Gear The gear was too big to mount in the lantern and so had to be provided remotely.

facing profile This lantern came from Newmarket Road, Cambridge. It was probably installed in the late 1960s/early 1970s so saw over forty years of service.

front profile The REVO Hyperion A featured a unique bowl catch. Two metal lugs were screwed onto the street-end of the bowl and engaged with a hinged catch at the end of the canopy. It didn't exert much pressure on the bowl but proved to be a good design as I never saw any Hyperions with missing or open bowls.

trailing profile The only modification to the lantern in service was the addition of a photocell. I had to replace the original bowl as it had sheered through by the lamp holder end of the lantern.

canopy The lantern had a wide canopy which tapered upwards where the bracket spigot entered the lantern.

logo The only identification marks on the lantern could be found on the canopy where "REVO Made In England" was cast in raised letters.

pedestrian view The 135W SOX lamp was shorter than the lantern body as the lantern was originally designed for the slightly longer 200W SLI/H lamp.

pedestrian view In this shot, the hinged bowl catch can be clearly seen. By 1963 the lantern was being offered in two slight variations with the hinge being located at either end of the lantern.

vertical This shot shows the slightly rimpled texture of the replacement bowl (which partly diffuses the downward light) and the white painted interior of the canopy.

interior #1 When opened, the bowl swings down to the column side of the lantern. The two lugs at the end of the canopy were for the second lampholder of the SLI/H lamp – these weren't included when SOI/H or SOX/H lamps were fitted.

interior #2 The spigot fixing method used two bolts and a metal clamp to secure the lantern to the bracket. Other internal fixtures were extremely minimal: the incoming power supply was connected to a porcelain terminal block on the lampholder support and there was no provision for an earth connection.

This REVO Hyperion A originally came from Newmarket Road, Cambridge. It was #46 and was probably installed in late 1969 when Newmarket Road was duelled and the Elizabeth Way bridge was built over the Cam.

The Newmarket Road installation was interesting as it appeared that the lighting engineer was trialling 150W SOX lanterns (later 135W SOX). A short run of Thorn Alpha 5s was then succeed by a run of REVO Hyperion As and then Philips/ELECO Goldenray GR150s.

It was removed as part of the Cambridgeshire PFI in late 2012. My thanks to Cambridgeshire County Council and Balfour Beatty for saving this lantern for me.

Unfortunately the bowl had split at one end of the lantern but the rest of the canopy was intact although a little dirty. It cleaned up well and I replaced the now-cloudy and split bowl with a new one.