Lighting and heating


When you switch on a light, have you ever wondered what is inside a light bulb?
The part of the light bulb which gives out light is called the filament. This is a coil of thin wire. The metal used to make the filament is called tungsten. If the filament was open to the air it would soon burn out, so it is placed in a glass bulb and the bulb filled with a gas called argon. The filament does not burn out quickly in this gas. The argon is held in place by the glass bulb. Glass is used because it is transparent and strong and does not let the gas pass through it and escape. Even when the filament is surrounded by argon it eventually burns out but it may give a thousand hours of light before it does.


Who invented the light bulb?
The light bulb was invented by two men between 1878 and 1879. They were the American Thomas A. Edison and the Englishman Sir Joseph Swan.


The world's first light bulb was produced by Sir Joseph Swan.
They each made a light bulb which had a carbon filament. The carbon filament was not successful because it burnt out quickly. So the search was on to find a longer-lasting filament otherwise light bulbs would not be useful. A range of metals was tried, but finally a filament made of tungsten was invented by the American William D. Coolidge in 1910. This worked for hundreds of hours an was reasonably cheap. It is the one we still use today.

Why are some light bulbs clear and some have got clouded glass?
The light bulbs which are clear are the traditional form of bulb. In the past this was what everyone had. Today they are often used in a glass lamp shade. The light passes thought the clear walls of the bulb and makes the lamp shade sparkle.
There are two kinds of clouded glass. One kind is called pearl and is used to make the light scatter more with less sparkle. It spreads out the light fairly evenly. The second kind of clouded glass makes the bulb white. This makes the light even less dazzling. It can be used in lamps without shades.

Do strip lights work in the same way as bulbs?
The answer to this depends on the kind of strip light.
The strip lights used in many bathroom lights above mirrors are simply tungsten wires inside long glass tubes instead of pear-shaped bulbs.
Larger and brighter strip lamps are called fluorescent lamps. They work completely differently from ordinary light bulbs.


A fluorescent lamp is a tube filled with gases that conduct electricity. The inside of the tube is coated with a fine layer of a chemical that can give out light when an electric current flows through the gas. So when a fluorescent lamp is lit, we do not see the gas inside glowing, but instead we see the coating on the glass glowing. This is why you cannot have a clear fluorescent tube.
The first fluorescent lights came into use in 1933.

Why are fluorescent lights used in schools instead of light bulbs?
Ordinary light bulbs (called incandescent bulbs) have a life of about 1000 hours. Fluorescent lights last for 7500 to 10,000 hours.
Although fluorescent lights are more expensive to buy than a light bulb they last much longer and use only a fifth as much electricity for the same light. This means they are much cheaper to use than light bulbs. Fluorescent lights are also used in kitchens because they give a brighter more even light for preparing meals. You will also find them in offices and factories, in bus and train stations and many other places.


Why does electricity produce heat in some wires and not in others?
The electricity flowing through the wires in a cable to a kettle produce little heat. When the current flows through the wires inside the kettle element a great deal of heat is produced.
The reason for this is that the wire in the kettle makes the flow of electricity slower and the current has to push harder to get through. As it pushes harder more heat is produced.
You can feel how heat is produced by gently opening the palm of your hand and rubbing the knuckles of your other hand gently across it. Now press harder with your knuckles and rub again. You should feel more heat.

Are the wires in an electric element made from the same metal as in cables?
No. The wires in cables are made of copper. Copper lets electricity flow easily. The wires in heating elements are made from metals such as tungsten which do not let electricity flow as easily but which also do not melt at high temperatures.

You can see the element in an electric bar fire but not in a convector heater. Has it got one?
Yes. The element is at the bottom of the convector heater. As the wire gets hot it heats the air and the air rises out of the top. Cooler air is sucked in from below. This also becomes hot and rises. Eventually the heater will fill the room with warm air.


Does an electric bar fire warm you in the same way as a convector heater?
No. The electric fire or radiator sends out rays of heat which strike your skin and warm it. The convector warms the air in contact with it. The warmed air then circulates around the room.

Does a microwave oven have a heating element?
No. It uses a kind of radio wave called microwaves. These enter the food and heat it up.