GEC Z3430
Lantern acquired in April 2004.
This lantern saw life (in every sense of the word) installed atop one of the high masts on Derby's Ring Road, where it was fitted to a cradle supporting three other Z3430s. These lanterns are believed to have replaced older lanterns that each ran 1 kW MBF lamps - imagine the energy saving made when the 400 Watt SON Z3430s were fitted! The reason that this lantern was removed is unknown, although it may have been out of action for a number of years before entering the Collection; indeed, one high mast had its lanterns removed for safety (and security) after the winch employed to raise the cradle up and down the mast became jammed whilst the cradle was situated at the bottom of the mast during a re-lamping session. The only way to release the winch was to hire in an extra-long access platform ("cherry picker"), and carry out repairs to the top of the winch, and such vehicles are neither in abundance, nor are they especially cheap to hire. In the end, the mast was decommissioned completely and several new 10 m columns were installed along the affected section of road. Nowadays, no Z3430s exist on Derbyshire roads at all; the Derby examples all disappearing when the high masts were renewed as part of Derby's Street Lighting PFI in November 2009.
The lantern is highly functional and industrial in appearance, with little in the way of aesthetic embellishment. The main lamp area is a polished aluminium hemispherical dome with a section housing the lamp control gear (literally) bolted to the side. A glass disc seals the bottom of the dome, whilst a cast aluminium lid clips to the top. An adaptor allows the lantern to attach to the wider 76 mm (3 inch) diameter bracket arms of the high mast cradles - the spigot entry of the lantern only allowing brackets with a maximum diameter of 42 mm (1.65 inch) to be accommodated.
The inside of the lamp area is painted white from the top to approximately halfway down the inside of the reflector, when the natural unpainted aluminium finish takes over. This must be a method of controlling glare from the lantern - the white providing slight diffusion from the luminous flux emitted directly from the lamp. A handwritten note on the underside of the gear section suggests that the lantern underwent considerable modification on Friday, 1st August 1997, in order to return it to lighting.
The other side of the gear section is also flat, and could accommodate a NEMA photocell socket. With the Derby installation, the high masts were all group-controlled from the photocell fitted to a Thorn Alpha 3 located near to the switch room that housed the immense distribution boards used in the operation of the Ring Road lighting.
Two stainless steel clips hold the cast aluminium lid in place. Owing to the possibility that the lantern may not be installed perpendicular to an adjacent carriageway, as regular street lighting lanterns tend to be, the lamp can be positioned at any angle within the optic; an arrow cast into the lid indicates the main beam angle.
The method for altering the main beam angle is very simple - with the lid removed, a small screw and clamp is revealed on the inside rim of the optic. Loosening the screw, and then moving the lamp, alters the angle - a slot on the underside of the lid prevents it from rotating once the clips are engaged.
The lamp assembly is also screwed to the inside of the lid. Notice that a relatively narrow lamp support is provided - this is only wide enough to accommodate tubular SON lamps; elliptical lamps would be too wide. This is probably a deliberate action, as the tubular lamps offer a more focused beam than an elliptical lamp would. Incidentally, the lamp seen here is dated to April 1997 (7D), which would be concurrent with the handwritten date seen earlier, though it also suggests that the lantern was never used after being repaired - perhaps, there were a few 'spare' lanterns available, should one become faulty in service. A part code cast into the underside of the lid (ZD4655/C) suggests that spare parts were available, though by 1997, GEC Street Lighting was nothing but a distant memory - the Z3430 did live on for a while, however, but became the WRTL HML 400 lantern.
Another sign that this lantern may have had limited use is the standard "Disconnect supply before servicing" clear adhesive label that GEC applied to many of its lanterns. On lanterns that have seen considerable use, the label may be missing completely, or the colour is missing from the text.
Removing the two (surprisingly, non-captive) screws that hold the cover to the rear section in place reveals the lamp control gear. The original GEC Z1885 ballast appears to have been removed as part of the 1997 refurbishment, with Thorn control gear being fitted instead. The imprint of the Z1885 is still visible on the inside of the cover, however. Despite the capacitor being date-stamped to February 1986, this too carries a handwritten date of August 1997, and so is also likely to have been installed then, probably as new, old stock. The final telltale sign that the lantern never ended up being used after the work was carried out is the lack of any corrosion or dirt to the individual components, and indeed, the lack of any insects or cobwebs within the gear area. Corrosion is visible on the part of the optic area that is surrounded by this section, however.
The lantern was attached to an AC Ford AC 872 Mk II wall bracket on Friday, 13th October 2017. Thanks to the functional nature of this lantern, the easiest way to install it was to disassemble it, and then to rebuild it on the bracket. The reassembly is captured in the animation below.
Conveniently, the lamp focus was already set correctly for the lantern's corner location in the room, and so this was left alone. Despite the 20-year gap between the new gear components being fitted and the lantern receiving a power supply, everything operated perfectly, and the lamp warmed up within a few minutes.
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 to rated wattage | Percentage Difference |
| 245.3 | 2.67 | 502 | 655 | 50 | 0.76 | 497.76 | 97.76 | 24 % |
Thorn Gamma 6 | Philips XGS 103
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