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Glossary terms used on this page

CFL bulbs

CFLs are compact fluorescent lamps. They operate on the same principle as fluorescent lights but the tube is folded into a more compact design so they are more versatile and can be used in devices designed to take traditional incandescent bulbs. They use about 80% less electricity than traditional bulbs to produce the same light and last considerably longer. Their mercury content means disposal, especially of broken bulbs, requires extra care. Also referred to as low-energy lightbulbs.

CO₂

CO₂, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO₂ to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO₂ is important. Burning fossil fuels releases CO₂ into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.

CO₂

CO₂, or carbon dioxide, is made up of the elements carbon and oxygen. It exists quite naturally in our atmosphere, as part of the carbon cycle. Everyday processes in the plant and animal world both add CO₂ to the atmosphere and take it out. However, because it is a greenhouse gas - meaning it affects the temperature of the earth - the exact level of CO₂ is important. Burning fossil fuels releases CO₂ into the atmosphere, hence the anxiety that extensive use of these fuels is causing climate change.

Carbon

Carbon is the fourth most common chemical element in the universe, and carbon compounds - in other words, carbon chemically combined with other elements - are the basis of all known life forms on earth. Pure carbon appears in many apparently diverse forms, from diamond to graphite to charcoal, but it is much more commonly found in substances such as coal, oil, natural gas, wood and peat that we use for fuel. When we burn these substances to provide energy - either directly in our homes as heat, or in power stations to produce electricity - the combustion process produces 'oxides' of carbon, including the gas CO₂.

Embodied energy

Embodied energy - sometimes referred to as 'embedded energy' - is the energy used (and therefore the CO₂ emissions) in manufacturing, packaging and transporting a product, material or service. So when calculating the CO₂ savings from a new energy-efficient product such as a boiler or washing machine, its embodied energy needs to be taken into account. Usually the energy saved in use will quickly compensate for the embodied energy, but in some cases - such as small urban wind turbines - it may be that a product will use more energy in its manufacture than it will save across its lifetime.

Energy efficient

definition to follow

Fluorescent lights

A fluorescent bulb or tube uses the flow of electricity to excite mercury vapour in an inert gas (argon or neon), which creates invisible ultraviolet light. A coating of phosphor on the inside of the glass then converts this into visible light - a process known as fluorescence. They have higher energy efficiency and longer life than traditional incandescent bulbs. See also CFLs/low-energy lightbulbs.

Greenhouse gases

Greenhouse gases raise the earth's temperature through the greenhouse effect. There are six main examples. As well as carbon dioxide, they include: water vapour, methane, nitrous oxide, ozone and CFCs (which include sulphur hexafluoride, HFCs, and PFCs). Of these, carbon dioxide, methane, nitrous oxide, sulphur hexafluoride, HFCs, and PFCs are controlled under the Kyoto Protocol to limit their concentration in the atmosphere. The heat warming capacity of each gas is measured by its 'global warming potential': how much heat it traps depends on its chemical make-up and how long it stays in the atmosphere.

Incandescent bulbs

Incandescents are traditional lightbulbs that use a filament (a thin thread of metal, usually tungsten wire) inside a glass bulb that glows white hot as electricity passes through it. The filament is prevented from burning either by creating a vacuum inside the bulb or filling it with inert gas. They are far less energy efficient than fluorescents/CFLs or LEDs because most of their radiation is given off as heat rather than visible light.

Kilowatt-hours (kWh)

A kilowatt-hour is an amount of energy equivalent to a power of one kilowatt (a thousand watts) running for one hour. The unit is commonly used on electricity meters. If you know how many kilowatt-hours of energy your household uses, you can translate this into kilograms of CO₂ emitted by multiplying it by 0.527. A megawatt hour (MWh) is an amount of energy equivalent to the power of one megawatt (a million watts) running for one hour. Similarly, a gigawatt hour (GWh) is a billion watts for one hour, and a terawatt hour (TWh) is a trillion. While your domestic gas bill will be set out in kWh, the output for a power station, for example, will obviously be expressed in one of these much larger units.

Mercury

Mercury (chemical symbol Hg) is a metal that is liquid at standard temperature and pressure. It is used in the manufacture of low-energy lightbulbs (CFLs and other fluorescent lights), and extra care must be taken in their disposal, especially when they are broken, because of mercury's toxicity.

Toxins

A toxin is a chemical compound from one organism that is harmful to another organism.

Watt

A watt is a unit of power. Power is the rate at which energy is used, and a watt is equal to a rate of one joule of energy per second. Watts are commonly used when referring to the energy consumption of relatively small things like lightbulbs, while kilowatts (a thousand watts) are used for larger machines. Megawatts (a million watts) are used to measure the electricity generation of power stations. See also kilowatt-hours.