Glass is the part of a ceiling light that decides what the light does. The lamp inside supplies the lumens; the glass decides whether they arrive as a soft wash or as a bright point you cannot comfortably look at. On a ceiling fitting, choose the glass first and everything else second.
A globe throws light in every direction, ceiling included, and makes a low room feel taller. A flat disc or plate sends nearly all of it downward — useful over a worktop, harsh as a room's only source. A dome sits between the two. A cylinder gives a defined column below and a faint ring above.
Under a 2.4 m ceiling, a flush glass fitting of 10-14 cm keeps the walkway clear. A 30 cm globe hangs into the room and belongs over furniture rather than in the middle of a corridor. With 2.7 m or more you can use a semi-flush fitting on a short stem, which lifts the glass off the ceiling and lets light wash upward as well as down.
Glass is heavy: a 40 cm shade reaches 3-4 kg, all of it carried by the ceiling rose fixing. Concrete takes it without comment; plasterboard needs a cavity fixing or a batten across the joists. If the shade is fully enclosed, use a lamp rated for enclosed fittings — trapped heat shortens the life of LED driver electronics long before it dims the light.
Opal. It hides the lamp completely and spreads the output evenly across the whole surface.
Around 1,500-2,000 lm for a 15 m² room, plus roughly ten per cent if the glass is heavily opal.
Isolate the circuit, let the glass cool, wash it in warm water with a drop of detergent and dry it fully before refitting. Abrasives leave a haze you only notice against the light.
For flat, ceiling-hugging shapes only, see the flush ceiling lights.
