An unusual feature of this lantern is that optical control is provided by a "Dielikon" (acrylic) refractor ring, which is composed of two separate injection-moulded rings that are glued together. The refractor prisms are on the inside of each ring; the outer sides are smooth, in order to allow for easy cleaning.
The lantern's canopy had been painted a dark green colour during its lifetime; this finish is now wearing away, and the aluminium is beginning to show through. Just visible in the canopy are four slightly raised sections - these act as strengtheners for the four screws that secure the refractor to the underside of the canopy.
Turning the lantern over, these four screws can be seen. Interestingly, they are positioned an equal distance apart, so the refractor could, in theory, be positioned in four ways in the lantern. Copper grease has been applied to the screws, in order to reduce the likelihood of them seizing. The ring is bottomless, and the lantern was never designed to be fitted with a bowl - it would never be allowed today, but back in the austere 1950s, the concept of open lanterns was still accepted.
The refractors are arranged in order that the majority of the lamp's luminous flux is, logically, emitted along the carriageway on both sides of the lantern. The lighting centres are the two small clear circles visible above. Some hairline cracks can be seen in the refractor - this is simply due to the age of the plastic. It is believed that the remaining Derby Murray's refractor broke away because of the cracks extending from the screws downwards, rather than through vandalism.
An 'Across Road' marker is also moulded into the plastic - this must be aligned with an arrow on the underside of the canopy to ensure correct orientation of the lantern when installed.
The other side of the refractor states that this is "Wardle No. 9951" - a part code, or date of manufacture? Either is possible.
Although the lampholder support bracket (and its holding screws) is heavily rusted, all can be removed without a problem. With the bracket taken away, the three focal positions can be seen - the lowest setting in the lantern (its current setting) is for 100 Watt GLS lamps; then, the middle setting is for 150 Watt GLS and 80 Watt MB/U lamps, and finally, the highest setting is for 200 Watt GLS and 125 Watt MB/U lamps. Interestingly, in Derby, the lamp setting would need to be set to the 150 Watt/200 Watt position, even for 100 Watt lamps, as the unique "Derby 100" lamps would not be correctly focused in the 100 Watt position, on account of their large size. What cannot be conveyed here is the oil smell that exists in the focusing area - it does not detract from the lantern at all; in fact, I think it adds to the old-fashioned charm of the design.
The lantern was fitted to a wall bracket on Friday, 6th July 2018. The bracket featured a 1′′ BSP right-angled bend fitted with a ¾′′ BSP reducer, and finally, a male-male coupler. Although the lantern's paint finish was worn, it was in good enough condition for the lantern not to require any restoration except for a cleaning of the refractor cylinder - made all the more easier by the prisms being moulded onto the inside of the plastic - a feature highlighted in sales advertisements for the lantern.
A 7 Watt GLS-shaped LED lamp was fitted - this provides a comparable lumen output to a traditional 60 Watt filament lamp. The two photographs below demonstrate the how the refractors help to diffuse the light output.
Lamp operation 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 |
| 240 | 0.04 | 6 | 10 | 49.8 | 0.64 | 6.14 | -0.86 | 12.23% |
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