Thorn Alpha 2000

Lantern acquired in November 2005.

This example was saved by Claire after a number were removed from the 'south' slip roads of the A38/A50 roundabout, just out of Derby, in mid-2005. Urbis ZX3 lanterns of the same wattage replaced the 2000s, which may raise questions as to why they were replaced in the first place - I believe it was because Philips MA 60s on the main part of the A38 had also been replaced, and so having all the lanterns the same created a uniformity. Despite the replacements, Alpha 2000s remained installed throughout the rest of the A50 through Derbyshire, on both the main carriageway, and on the adjoining sliproads, until the early 2020s, when LED replacements began to see their numbers diminish rapidly. A notable Alpha 2000 scheme elsewhere in the UK was that of the Blackpool Promenade, which was relit with these lanterns (painted maroon) in the mid-1990s. Subsequently, most were replaced with WRTL Vectras. Outside of the UK, the lantern was known as the Thorn Carat.

The lanterns all had flat glass covers, and because of this, the columns were positioned slightly more closely together, owing to the reduced light spread between columns. The Alpha 2000s were, however, some of the first cut-off lanterns to be seen in Derbyshire. This, combined with their all-aluminium construction and unpainted galvanised columns, gave the appearance of absolute modernity in the early days of the A50.

For some reason, Alpha 2000s have a removable panel at the front of the canopy - I thought it might be a way of changing the lamp without having to lift the whole canopy; however, the panel is screwed in place, and so, the canopy would still need to be opened! The lanterns were all group-switched, negating the need for individual photocells. Despite this, the intended position for a NEMA socket is visible on the canopy.

The Alpha 2000 is something of the evolution of the Pilote, and employs a similar satin-effect aluminium reflector. This style of reflector, along with the choices of flat or curved glass, or polycarbonate bowl, are also common to the contemporary Riviera lantern, although I suspect that the Alpha 2000 was a more expensive product, owing to its aluminium construction, compared to the plastic employed in the Riviera.

This view demonstrates the three bolts that hold the removable section of the canopy in position. In fact, a bead of silicone sealant exists in the join between the two parts of the canopy too - just to ensure that the two pieces cannot be separated easily. The internal position of the NEMA socket is visible here too.

The optic is sealed to a tightness of IP65, and the inside of the lantern is slightly lower at IP54; however, the lantern had been up for nine years, and yet very little dirt had gathered inside during that time. Considerable space is available behind the optic to accommodate the lamp control gear and associated wiring.

The lantern's tilt is adjustable, thanks to the two grub screws and a plate carrying indicator arrows that is located at the top of the picture. Here, it is set to zero degrees, which takes the five degree upward tilt of the bracket into account. The control gear components are attached to a removable tray, with the ballast on the left, and the ignitor and capacitor on the right. The black-sheathed rubber flex further to the right has cores of brown, black and grey, and connects the components to the lampholder.

 The ignitor should be secured to the tray, and be positioned beneath the capacitor, but its plastic thread has broken, causing the component to hang loosely within the lantern. Just visible on the capacitor's casing is the date code '5195', representing the 51st week of 1995 - the 18th - 24th December.

Two date wheels on the lower casting indicate that it was produced in February 1996, which tallies with the majority of the A50 opening a year later.

The rubber flex terminates into a sealed connector, which in turn, connects with the bung that seals the optic ordinarily. Rotating this a short distance anticlockwise disconnects the supply to the lampholder, and also allows removal of the assembly, to facilitate lamp replacement, etc.. The '2002' sticker indicates the last time that the lantern was re-lamped when in actual use on the slip road.

The optic rests on the thick gasket that exists around the flat glass cover under normal circumstances, with four clamps spaced around it holding everything together.

The plastic body of the optic includes a lip that presses onto the gasket. Despite the (supposedly) dust-proof nature of this area, the inside of the glass was rather dusty, and so I cleaned both it and the reflector surrounds while the optic was in a state of disassembly.

The lantern was fitted to an AC Ford AC 872 wall bracket on Friday, 27th October 2006. Originally I had planned to install the Holophane Syracuse Medium in this place; however, this proved too fiddly to accomplish and so the Alpha 2000 was chosen as a last-minute replacement. The lantern only just fitted the available space!

It may actually have been a good idea to install this 'Thorn between two roses' in this location - firstly, it means that I get to make up awful puns like that; and secondly, the lantern is just below its (spiritual) ancestor - the Thorn Alpha 3.

To the left is the Urbis ZX3; to the right we have the Philips 'Iridium' SGS 253.

All three lanterns were then powered up - it is interesting to be able to compare the optics in this way.

Lantern warm-up video:

Testing 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 to rated wattage Percentage Difference
237.9 0.8 168 190 50 0.86 163.68 13.68 9%

Atlas Alpha 8 | Holophane Syracuse Medium




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