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Alpha Eight

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Date: Mid 1960s - Mid 2000s

Manufacturers: Atlas/AEI/Thorn

Type: High Pressure Sodium, Mercury Vapour

Successor: Civic


The Alpha 8 was a main road mercury and High Pressure Sodium lantern and the design changed dramatically over the lantern's production run. The Mark I is a completely different lantern to the similar Mark II and III versions.

Contents

Mk I

The Atlas Alpha 8 is described in a cataloguedated post 1964 although it is not known precisely when it first entered production. It is not known when production ceased but it is likely to have been by the mid 1970s.

The Atlas Alpha 8 (not to be confused with the later Thorn variants listed below) was designed as a twin lamp mercury lantern. 2x 250/400W MBF lamps (or any combination of) could be accommodated in the lantern.

The lantern design was unusual in that the bowl was permanently fixed to the canopy, with the lamps being accessed by a hinged opening in the top of the canopy. The canopy was cast in aluminium alloy with a separate shoe (much like the Alpha 1) attaching the canopy to the column spigot.

Anodised aluminium reflectors were located above the lamps.

The control gear for the lamps is remote to the lantern. The individual lamps could be arranged to be switched independently by a time switch to reduce the lighting level and hence power consumption after midnight for example.

Atlas Alpha 8s were used to light Marble Arch in London, although by the end of their lives they had been converted to run SON lamps and fitted with a NEMA cell. One of the few in collections is one of these lanterns.

There are few surviving photographs of Atlas Alpha 8s so little is known where they were used. Derby did use them and one sole surviving disused example is believed to still survive.

Mk II

There was a short gap in the early 70s in which the Alpha 8 was not displayed in the Thorn catalogues[1] but in the mid 70s, the Alpha 8 returned with a new design that was much more compact.

The Thorn Alpha 8 Mk II is a completely different lantern to the original Atlas design.

The MkII can be considered a 1st generation SON lantern although it could also run MBF lamps.

Constructed with a cast aluminium canopy and again using a separate “shoe” (as on the Alpha 1) to attach the lantern to the column. This shoe also contained the control gear for the lantern. A hinged panel on the underside of the shoe allows access to the control gear.

The canopy contains two anodised and dimpled reflectors to produce a cross over beam distribution, this together with the high positioning of the lamp within the canopy reduced glare and allowed either semi or full cut off distributions.

2 types of bowl were available, clear and another with longitudinal refractor grooves on the bottom surface. It is believed that this was the original design of bowl. The bowl is hinged at the column end of the lantern and fastened with a plastic clip “roadside”.

As the lanterns aged, this clip often became brittle and would snap, the bowl would then be lost, leading to lantern replacement.

Early Mark II lanterns were in plain aluminium finish but later versions were available with a white painted canopy and grey painted shoe.

Mk III

In 1986, the Alpha Mk3 was launched and was one of the first lanterns to have a full GRP canopy. It was primarily designed for SON-T as apposed to SON-E lamps though the latter could still be used if preferred.

The lantern was redesigned to have a canopy made of GRP which was also enlarged to house the control gear, meaning there was no separate shoe as on the Mark II.

The control gear is attached to an aluminium base plate which also contains the spigot housing. Opening the canopy, pivots the entire canopy and bowl forwards for access to the gear.

For re-lamping, just the bowl needs to be opened. The optical arrangement is very similar to the Mark II version.

Standard finish for the Mark III is white GRP with a black base plate although all black versions have also been seen. Bowled and flat glass FCO versions are available.

The Mark III was superseded by the Thorn Civic lantern which was of a more modern design and better optical performance. It is believed production of the Alpha 8 was discontinued in around 2004, with WRTL offering it as the MRL 8 for a short period. It is however no longer produced.

Successors

By the millenium the Alpha 8 was being viewed as old technology. Thorn had released the more contemporary Civic and Riviera lanterns which finally put an end to the Alpha 8's production.

External Links

In Situ

Catalogues

In Collection