Are these shades on their own or complete lamps?

Mostly complete fittings. Lamp appears in 720 of the 1,280 titles, brass in 407 and glass in 278, so the usual thing on offer is a base or a pendant sold with its shade. Bare shades do exist in the category. Shades appears in 125 titles and glass shades in 32, and a pair of shades with no fitting sits at the bottom of the range.

What period does most of this lighting come from?

The 19th and early 20th centuries. Of the listings with a clean year, the range runs 1800 to 1940, and the 1920s and 1930s are the two busiest decades by a clear margin, followed by the 1910s and 1900s. A large slice carries an era label rather than a year: 19th Century in 154 titles, Edwardian in 116, Victorian in 83. Those are approximate, and some sampled titles carry a century label that sits oddly with the description or the dated field.

Which shade glasses get named by dealers?

Ribbed prismatic glass leads, in 44 titles. Moonstone, opaline, cut glass, vaseline and cranberry all recur, and colour gets named often for such short titles: cranberry in 53, vaseline in 35, blue in 32, with amber, ruby and peach in the samples. Where a named glass appears, it tends to sit above a plain frosted equivalent of the same shape.

Do many listings say rewired or PAT tested?

Rewired turns up in 154 titles, PAT tested in 38. Both cluster on the ready-to-hang stock, meaning pendants, ceiling lights and table lamps. They appear far less on unconverted oil lamps and on bare shades, which come to market as objects rather than working fittings.

What are the biggest pieces in this category?

Architectural lighting rather than domestic. Billiard and snooker lights, 26-inch hall lights and a 24-inch rise-and-fall chandelier sit at the very top, along with a pair of porcelain vase lamps standing 90cm. Large appears in 74 titles, and the biggest sampled pieces state their dimensions in the title.

Is this category the province of a few specialists?

No. Around 143 listings a year come to market on Sellingantiques, and 181 different dealers have listed in the category. That breadth shows in the stock. Alongside the brass table lamps and glass pendants sit one-offs: an oil lamp with a terrestrial globe as its shade, a copper railway hanging lantern, a newel-post lamp with an acid-etched shade, and a cast-iron "witches hat" ceiling light from a named country house.