REVO/Relite/Simplex 'Diadem-Major' 80w/125w MBF Lantern. Originally designed and produced by REVO of Tipton for use on minor roads, this is the geared version of the 'Diadem' side-entry lantern. Of the two lanterns, the 'Diadem-Major' proved to be the least popular, but found favour in suburban and rural locations where it was more difficult to accommodate externally mounted control-gear, for example, on wood pole mounted brackets or on the sides of buildings. The lantern had a reasonably long production run, but manufacture finally ended in the 1980's; the very last models being supplied in a blue painted finish, rather than the natural aluminium finish of the earlier models.

Of cast aluminium construction, the Diadem-Major was almost twice the length of the remote-geared 'Diadem' and much heavier, but shared the same type of lozenge-shaped prismatic bowl. Access to the lamp is identical for both types of lantern, and is made by releasing the toggle-action side catch, allowing the bowl to hinge downward on its side-mounted hinge. Earlier versions of the lantern used prismatic glass bowls, but these were superseded by prismatic plastic look-a-likes; sadly, the plastic versions tend to 'yellow' over time due to the UV rays emitted from the mercury lamps. The hinge that's moulded into the side of the plastic bowl is another weakness; being easily broken if forced. It's understood that replacement plastic bowls for these lanterns were still available from WRTL in 2005.

Access to the control-gear on the Diadem-Major is gained by releasing two captive-screws in the access door mounted beneath the lantern (directly behind the bowl); the door can then be hinged down on its rear mounted hinge to give access to the control-gear. Another problem the Diadem-Major suffers from over time is the corroding of the thin steel door cover; however, later examples had galvanised access doors, which faired better against corrosion. Fortunately, a new and unused access door was acquired with the lantern and a new replacement bowl has also been sourced; these will be used in the lantern's eventual restoration.

The ex Dolgellau Simplex Diadem-Major is seen in acquired condition. The 'yellowed' plastic bowl and badly corroded control-gear access door are clearly visible. The earlier versions of this lantern had a slightly different underside shape to the casting where the door is situated.

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An in-service Diadem-Major lantern in Dolgellau, North Wales. Although dwindling in numbers, some of Gwynedds' Diadem-Majors have been converted to run 50w SON lamps, instead of 125w MBF lamps, so these may see an extended life.