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ELECO GR501
Genre: Enclosed Horizontal Traverse Low Pressure Sodium Lantern
The low pressure sodium discharge lamp was developed by Philips in 1932. After two successful trial installations
(including the first low pressure sodium installation in the UK along the Purley Way, Croydon) the first commercial installation
was installed by Liverpool Council in 1933 using specially commissioned lanterns from Wardle.
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 GR501
Date: Late 1970s - Late 1980s
Dimensions: Length: 23½", Width: 5 5/8", Height: 6½"
Light Distibution: Semi Cut-Off (BS 1788:1964)
Lamp: 35-55W SOX
History
DAVIS catalogue
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ELECO was one of the most prolific manufacturers of low pressure sodium lanterns producing two separate
families of lanterns each called Golden Ray. The first was a selection of typical deep-bowl "boxy" lanterns,
which originally appeared in the 1950s, the lengthy dimensions were required to hold the cumbersome leak transformers and gear of the period.
By the 1960s, a new family of Golden Ray lanterns appeared, with sleek angular aluminium canopies and equally slim
elegant bowls.
The GR501 was ELECO's specified gearless lantern for Group 'B' roads, and it accepted both 35W
and 55W bulbs. It wasn’t until the 1970s that smaller lanterns were designed just for the 35W SOX bulb: the first were the gear-in-head
GR525 lanterns and these were followed by the gearless GR535.
Unlike other members of the family, this lantern didn't have a ridged spine, instead having a smooth canopy.
The lantern was modified slightly over its lifetime. The bowl securing mechanism was changed (I have a spare bowl which doesn't have hinge extrusions) whilst
the bulb holder position was later moved to the road-side end of the lantern (the GR5011).
When ELECO Holdings transferred the manufacturing of their street lighting to subsidiary
DAVIS, the GR501 remained in the catalogue. But the lantern was finally discontinued when the remnants
of the original ELECO range was absorbed into Whitecroft lighting in the 1990s.
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Popularity
ELECO lanterns were popular throughout the UK, and the GR501 could be found installed on Group 'B'
roads throughout the country. It wasn’t as popular as the contemporary Thorn or Philips lanterns, but still enjoyed widespread use.
Identification
The lantern is easily identified by its size and profile. It also has the ELECO logo cast into the top of the canopy.
Optical System
The primary optical system comprised of two plate refractors positioned either side of the bulb. As the low pressure
sodium lantern already casts a wide beam in azimuth, the horizontal refractors simply alter the flux elevation by
fashioning two main beams in a semi-cut-off distribution (in accordance with BS 1788:1964).
The interior of the canopy is unpainted aluminium. This secondary optical system reflects any flux emitted above
the horizontal back toward the ground.
The exterior of the bowl is smooth to facilitate easy cleaning.
Gear
The lantern was never designed to carry gear – which is why the lantern is so small and sleek.
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facing profile
The ELECO GR501 was Cambridge County Council’s lantern for choice for new developments from the
mid-1970s through to the early 1990s. Several of these lanterns were installed on Concrete Utilities columns in Chivers Way, a new
road driven through the site of the old Chivers jam factory, in 1986.
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front profile
The first column was struck by a lorry turning into the new building site and the column was left standing at a
precarious angle. When the service was disconnected, the column was felled and moved to derelict ground. Therefore I
liberated the lantern; and it was the first lantern in my collection.
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trailing profile
As it was relatively new when I obtained it, the lantern was in excellent condition and didn’t require
any restoration work. The P42 two-part photocell was retained as the lantern was usually supplied with it.
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canopy
The bowl was in very good condition with no appreciable discolouration.
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logo
As with most ELECO lanterns, the maker’s logo was cast into the lantern’s canopy.
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pedestrian view
The bowl’s angled sizes were designed to position the refractor plates in the ideal position with respect to
the bulb. The rest of the area of the bowl was slightly frosted, thus diffusing the light from all the other parts of the bowl.
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vertical
The manufacturer’s name was also cast into the rim of the bowl. It states: "GR 501 ELECO LTD. St. Albans".
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open bowl
The interior of the lantern clearly shows how the untreated aluminium-silicon alloy canopy could act as a secondary reflector. As with
earlier ELECO low-pressure sodium lanterns, the bulb holder was house side. The five block terminal strip was standard
and carried connections for the bulb and photocell; the earth connection was made directly to the canopy.
I have fitted the lantern with the smaller 35W SOX option. This is a nod to Cambridgeshire County Council who also used 35W SOX bulbs in their
larger 55W SOX lanterns.
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ELECO GR501: Night Burning
When I took this shot, the bulb was flickering badly and I think this effected the exposure. (It's much darker than another half-second exposure
taken for the GR535). When I examined the bulb the next morning, the interior of the outer tube was completely black. The inner tube had failed,
hot sodium vapour had escaped into the outer tube, and started attacking the interior of the glass. A fresh bulb was used for all the other shots on
this page.
ELECO GR501: As Aquired
A popular lantern, the ELECO GR 501 borrowed the lines of its larger siblings, scaling itself down
for side road mounting.
This was the lantern of choice for Cambridge County Council in the mid 1980s through to the early 1990s.
It was rescued from a knocked-down column in Chivers Way in Histon, Cambridgeshire in the late 1980s.
This lantern as kept extremely well over the years. Apart from a sporadic clean, it's never required any major work.
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