Glass is a hard, transparent strong yet brittle material. When it is molten it can be easily shaped and is used for making all kinds of electric lights. Glass is also an insulator.
A light bulb is made by dropping a lump of molten glass into a mould. The mould has the shape of a light bulb. Air is blown into the glass and makes a large bubble that pushes the glass into the sides of the mould. As the glass cools it takes up the shape of the mould and when it is released it has a light bulb shape.
Automated machines can produce a thousand light bulbs a minute.
Although glass is brittle, it is also very strong. Glass is used in windows. It is only liable to break if it is given a hard tap. You can see how strong glass can be when you see it used as television tables and as roofing glass panels.