Electric lighting devices
In an incandescent lamp, a tungsten conductor heats up when current flows and gives light; it is cheap, but its life is up to 1000 hours and most of the electric energy becomes heat, not light. A halogen lamp is also an incandescent type, but its bulb holds bromine or iodine vapour, so it lasts 2000–4000 hours. In a fluorescent lamp a glass tube whose inside wall is coated with phosphor is filled with argon and contains a little mercury; it saves energy, but mercury vapour is poisonous, so the lamp must not go into ordinary rubbish and is handed to a special collection point. A neon lamp is filled with an inert gas, needs a high-voltage transformer and is fragile. An LED lamp contains no mercury, is very economical, lasts tens of thousands of hours and withstands shocks, but costs more at first. Before replacing a lamp, switch it off, let it cool and ask an adult for help; do not pick up a broken tube with bare hands.
List the lamps at home: which type is in which room and roughly what power. Collect them in a class table and discuss which types are economical. Changing lamps and touching sockets is for adults: do not do it by yourself.