Topic: Sowerby glass identification

[Edenside#1]

Can anyone identify this Sowerby glass item, which bears a label stating "Optical stepped 8 3/8 inches with side sector" it has concentric rings with the rings offset in a quadrant shape on one side - presumably the side sector referred to. Thought to be from the 1950's era.

[Mosquito]

It looks like a lens from some kind of light/ lantern to me. The thicker sector presumably being to direct the beam. No idea of where it would be used though -- best guesses would be industrial or maybe maritime.

Steven

[Edenside#1]

yes that was my thought. When Sowerby were bought out by Suntex in the 1950's I think they moved over to the production of lamp lenses and I wondered if this could be one such? Does anyone understand the wording?
I'll post some clearer photos.