Holophane's Duo-Dome lantern was an open-type luminaire for GLS or MB/U lamps. It featured a simple construction, with a two-piece dome refractor attached to the lanterns body. Two sizes were available: a small size for group "B" lighting, or a large size for group "A" lighting.

Derby

Two Duo-Dome lanterns exist on ornate wall brackets on Nelson street. It appears they are both supplied from the building, if they haven't been disconnected.

They appear to now have SON-I or SON-E lamps in, but previously were fitted with tungsten lamps.

A much larger lamp is situated in the second lantern, perhaps a higher wattage.

The recent retrofit to SON, and the subsequent application of photocell controls means these may still be operational.