Lantern acquired in May 2004.

This lantern was used to light a section of Derby City Council's Stores Road depot. It dates from 1965 according to a date on the bowl. The replacement lantern was a WRTL MRL 6, and had a metal halide lamp fitted. Archival photographs suggest that Z8430CMs saw moderate usage around Derby, particularly on main roads around the Pear Tree and Normanton areas, where the lanterns were attached to the support poles for the overhead wiring that supplied Derby's trolleybuses, and this lantern could have been installed within the City before being re-used at the depot, particularly as the trolleybus operation ceased in 1967.

These first two pictures show sections the column and bracket that the Z8430CM was on whilst in service. Unfortunately, I didn't manage to get the image of the lantern in the reflection of the new van's window (on the left)!

From the side, the similarities to the later Z8896 side road lantern can be seen. Glass was the default bowl type, rather than polycarbonate, making this quite a heavy lantern. The bowl catch is also slightly different. The 'CM' prefix identifies this lantern as utilising a revised bowl design that was optimised for Corrected Mercury Vapour lamps; the original Z8430 having been designed for uncoated MA/V-type lamps.


The only difference in the appearance to the Z8896 is that, on top of the lantern is the addition of the GEC logo. No hole has been drilled in the canopy for a photocell as the lantern ran on a time switch.


Inside, however, the lantern is very different. Firstly, the lamp is mounted by the cable entry, rather than opposite. Also, the addition of reflector panels on either side of the lantern helps to focus the light out of the lantern. The gasket around the rim of the lantern appears to be some kind of rope - quite possibly made from that wonderful cancer-causing material known as asbestos. This may also be the material that was used to insulate the wires going to the lampholder - great! Of further note is the lamp that was fitted - this is a GEC 'Truelite' 250 Watt MBF dating from April 1978. Needless to say, by the time that the lantern was retired into the Collection, this lamp's arc tube was considerably blackened!


The bowl is offset slightly in relation to its aluminium support ring.


Just for size comparison, I put the Z8896 next to the Z8430CM. Notice that the Z8896 does not have as curved a canopy as the Z8430CM has. Maybe, then, the Z8896 is actually the larger version of the earlier design - the Z8591.


Restoration of the lantern took place on Thursday, 17th June 2005.


The canopy was cleaned and then painted, both inside and out.


The porcelain components were also cleaned, although the marks on the lampholder could not be removed. Notice the new gasket around the rim - better to be safe than sorry!


The bowl required little cleaning although some small specks of dirt had become trapped between the refractors. Once these were removed, the bowl was left to dry out and was then fitted back into the aluminium supporting rim.


The lantern was mounted to an AC Ford AC872 wall bracket on Tuesday, 9th August 2005.


On Thursday, 10th November 2005, the lantern was finally able to be powered up.


Following the acquisition of a second Z8430CM in April 2009, this example was taken out of service, awaiting the day when it could return to service in some form. This day arrived nine years later, in April 2018, when it was fitted to another wall bracket.


This time, however, it was fitted with 250 Watt SON gear, as I was interested to see how the lantern would look whilst running a light source with an output colour that differed greatly from the previous cool-white of the mercury lamp...I suppose that the answer is "much as the below picture illustrates"!


An OSRAM 250 Watt SON-E lamp is fitted here.


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
242.4 1.6 322 388 49.8 0.82 318.03 68.03 27.21%

Thanks to the compatibility between high pressure sodium and metal halide lamp control gear, the Z8430CM is able to run a 250 Watt HQI-E lamp as an alternative. The output appearance is very similar to the lantern's previous MBF incarnation, with a slight reduction in the amount of blue light emitted.


Testing the lantern again 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 1.54 357 378 49.9 0.94 355.10 105.10 42.04%

This video demonstrates the difference in warm-up between the two lamps. Notice that the more modern metal halide lamp is operating at full power within only a few minutes.

WRTL 2015 | GEC Z5670




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