Abacus AM480

Lantern acquired in June 2006.

This lantern came from around the London Road entrance to the Eagle Shopping Centre (more recently, Westfield and Intu) in Derby; it was one of several installed in the early 1990s as part of the refurbishment of the area known locally as "The Spot"; a wedge of land where London Road, Osmaston Road and St Peter's Street converge. The refurbishment saw a faux Art Deco stone structure incorporating a clock added to the open space above the site's subterranean public toilets, with these far more modern-looking lanterns. This particular lantern was removed from service in the mid-2000s as construction work began to commence on London Road, owing to the extension of the shopping centre at this time. The remainder of the lanterns would be removed around a decade later, when The Spot underwent further (controversial) remodelling, which included the demolition of the toilets and stone structure.

This first photograph, taken in autumn 1996, shows an AM480 (over to the right) attached to its unusual bottle green column, with the clock structure being visible nearby. Taking centre stage in the photograph is Derby City Transport's Volvo Citybus / Northern Counties 149 (E149BTO), freshly refurbished into the short-lived 'City Rider' livery, and travelling along St Peter's Street on route C35 to Blagreaves Lane.


For a while after acquisition, the identity of this lantern was unknown - there are no product labels anywhere on it. I had thought that the lantern may have been a WRTL 2310, which is similar in design, except that the AM480 does not have external vertical support bars as the WRTL product does. The lantern employs aluminium for its canopy and base sections, with a thick polycarbonate cylinder linking the two. The aluminium showed signs of corrosion, where the green paint had flaked off over time. A series of aluminium refractor louvres are angled to direct the majority of the lantern's output downwards, and whilst the transparent cylinder section extends beyond the canopy's widest point, the lantern is not designed in such a way that much light would pass through this 'window' section. A Royce Thompson P9 column-mounted photocell would switch the lantern on and off as necessary - the lantern itself being unable to accommodate a photocell, owing to its construction.


With the canopy, cylinder and refractor assembly removed, the lantern's construction begins to be revealed. An upward-facing Edison Screw Lampholder is surrounded by a tripod, on top of which is welded a short section of pipe. The canopy screws down onto this. An aluminium cylinder below the lampholder conceals the lamp control gear and internal wiring.


Removing this cylinder reveals the ABB-branded Vossloh-Schwabe 50 / 70 W ballast on one side of the base section.


On the other side, the ignitor and capacitor (manufactured in December 1992 and May 1993 respectively) are fitted. A small modification to the incoming wiring has been made - this sees the photocell connected ahead of any other components, in order for the lantern to be switched automatically.


The lantern was disassembled in October 2018 in preparation for the restoration of the corroded external parts. These returned to me on Friday, 16th November. The aluminium was bead blasted and then repainted the same shade of green as had been applied originally. The canopy, base casting ring and photocell casting were included in this work.


The underside of the canopy was repainted gloss white.


The spigot part of the lantern (which also forms part of the lantern's internal assembly) attaches to the base casting ring. As this was free from corrosion, it was not sent away for refurbishment; consequently, its finish is slightly more matted than the rest of the lantern is. After the polycarbonate cylinder was given an extensive cleaning in warm, soapy water, the individual discs that made up the refractor were cleaned and polished. With this work complete, the lantern was reassembled, fitted to a post-top stand and wired up (the photocell no longer being connected)...oh, and a lamp was fitted too!


Once switched on, the lamp warmed up within a few minutes, and the combination of reflector and refractor technology worked in unison to produce a beam that was concentrated largely on the floor below.


Lamp warm-up video:

Testing the lantern with my energy monitoring device revealed the following results:

Test Voltage (V) Current being drawn at full power (A) Measured wattage (W) Apparent Power (VA) Frequency (Hz) Power Factor True Power (W) Difference (W) Percentage Difference
241.7 0.7 97 169 49.8 0.55 93.05 23.05 33%

Philips MU 80 | Revo Diadem




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