Prior to the mid-19th century, most candles were made from tallow (a byproduct of beef-fat rendering). Nowadays, they are usually made from wax. Paraffin wax is the most common, but there are also candles made from gel, soya and beeswax.
The heat of the match used to light the candle melts and vaporizes a small amount of fuel. Once vaporized, the fuel combines with oxygen in the atmosphere to form a flame. This flame provides sufficient heat to keep the candle burning via a self-sustaining chain of events: the heat of the flame melts the top of the mass of solid fuel, the liquified fuel then moves upward through the wick via capillary action, and the liquified fuel is then vaporized to burn within the candle's flame.
The burning of the fuel takes place in several distinct regions (as evidenced by the various colors that can be seen within the candle's flame). Within the bluer regions, hydrogen is being separated from the fuel and burned to form water vapor. The brighter, yellower part of the flame is the remaining carbon being oxidized to form carbon dioxide.
As the mass of solid fuel is melted and consumed, the candle grows shorter. Portions of the wick that are not evaporating the liquid fuel are consumed in the flame, limiting the exposed length of the wick and keeping the temperature and rate of fuel consumption even. Some wicks require manual trimming with scissors or a wick trimmer for even burning.
In Rome, around the first century, candles were made out of tallow and the pith of rushes. The Latin word "candere" means to flicker. The Egyptians and Cretans made the candle from beeswax, as early as 3000 BC. The early candle was made from various forms of natural fat, tallow, and wax. In the 18th century, spermaceti, oil produced by the sperm whale, was used to produce a superior candle. Late in the 18th century, colza oil and rapeseed oil came into use as much cheaper substitutes. Paraffin was first distilled in 1830, and revolutionized candle-making, as it was an inexpensive material which produced a high-quality, odorless candle that burned reasonably cleanly. The industry was devastated soon after, however, by the distillation of kerosene (confusingly also called paraffin oil or just paraffin). Recently resin based candles that are freestanding and transparent have been developed, with the claim that they burn longer than traditional paraffin candles.
Before the advent of electricity, candles and oil lamps were used for illumination. Until the 19th century, candles were more common in northern Europe. In southern Europe and the Mediterranean, oil lamps predominated. Today, candles are used mainly for their aesthetic value and scent, particularly to set a soft, warm, or romantic ambiance, and for emergency lighting during electrical power failures. Scented candle are used in aromatherapy.
Candles are used in the religious ceremonies of many faiths.
Candles are a traditional part of Buddhist ritual observances. Along with incense and flowers, candles (or some other type of light source, such as butter lamps) are placed before Buddhist shrines or images of the Buddha as a show of respect. They may also be accompanied by offerings of food and drink. The light of the candles is described as representing the light of the Buddha's teachings, echoing the metaphor of light used in various Buddhist scriptures. See Ubon Ratchathani Candle Festival for an example of a Buddhist festival that makes extensive use of candles.
A diya, or clay lamp, is frequently used in Hindu celebrations and forms an integral part in many social rites. It is a strong symbol of enlightenment and prosperity.
Traditional diyas have now evolved into a form wherein waxes are being used as replacements for oils.
In Christianity the candle is commonly used in worship both for decoration and ambiance, and as a symbol that represent the light of God or, specifically, the light of Christ. The altar candle is often placed on the altar, usually in pairs. Candles are also carried in processions, especially to either side of the processional cross. A Votive candle or taper may be lit as an accompaniment to prayer.
Candles are lit by worshippers in front of icons in Eastern Orthodox, Oriental Orthodox, Eastern Catholic and other churches. This is referred to as "offering a candle", because the candle is a symbol of the worshiper offering himself or herself to God (and proceeds from the sale of the candle are offerings by the faithful which go to help the church). Among the Eastern Orthodox, there are times when the entire congregation stands holding lit tapers, such as during the reading of the Matins Gospels on Good Friday, the Lamentations on Holy Saturday, funerals, Memorial services, etc.
In the Roman Catholic Church a liturgical candle must be made of at least 51% beeswax, the remainder may be paraffin or some other substance. In the Orthodox Church, the tapers offered should be 100% beeswax, unless poverty makes this impossible. For this reason, the stumps from burned candles are usually saved and melted down to make new candles.
In some Western churches, a special candle known as the Paschal candle, specifically represents the Resurrected Christ and is lit only at Easter, funerals, and baptisms. In the Eastern Orthodox Church, during Bright Week (Easter Week) the priest holds a special Paschal trikirion (triple candlestick) and the deacon holds a large candle during all of the services at which they serve.
In Judaism, a pair of candles are lit on Friday evening prior to the start of the weekly Sabbath celebration. On Saturday night, a special candle with several wicks is lit for the Havdalah ritual marking the end of the Sabbath and the beginning of the new week.
The eight-day holiday of Hanukkah, also known as the Festival of Lights, is celebrated by lighting a special candelabrum or Hanukkiyah each night to commemorate the rededication of the Temple in Jerusalem.
A memorial candle is lit on the Yahrtzeit, or anniversary of the death of a loved one according to the Hebrew calendar. The candle burns for 24 hours. A memorial candle is also lit on Yom HaShoah, a day of remembrance for all those who perished in the Holocaust.
With the fairly consistent and measurable burning of a candle, a common use was to tell the time. The candle designed for this purpose might have time measurements, usually in hours, marked along the wax. The Sung dynasty in China (960–1279) used candle-clocks. By the 18th century, candle-clocks were being made with weights set into the sides of the candle. As the candle melted, the weights fell off and made a noise as they fell into a bowl. A form of candle-clock was used in coal-mining until the 20th century.
In the days leading to Christmas some people burn a candle a set amount to represent each day, as marked on the candle. The type of candle used in this way is called the Advent candle, although this term is also used to refer to a candle that decorates an Advent wreath.
A candle typically produces about 13 lumens of visible light and 40 watts of heat, although this can vary depending primarily on the characteristics of the candle wick. For comparison, note that a 40 watt incandescent light bulb produces approximately 500 lumens for the same amount of power. The modern SI unit of luminous intensity, the candela, was based on an older unit called the candlepower, which represented the luminous intensity emitted by a candle made to particular specifications (a "standard candle"). The modern unit is defined in a more precise and repeatable way, but was chosen such that a candle's luminous intensity is still about one candela.
It is commonly believed that the candle made of beeswax burn more cleanly than petroleum based paraffin waxes. However highly-refined paraffin wax can burn as or more cleanly (with regards to particulates created during combustion) than natural waxes. The type of wick and inclusion of any scents and/or dyes have a much greater impact on the release of compounds, particulates, and smoke, regardless of the base material. The cleanest burning candle will therefore be unscented, undyed, and a well constructed candle burning in a draft free area. Furthermore, a candle will function well when formulated waxes are blended together (soy, paraffin and other waxes) and fragrance oils along with wick selections are balanced properly.
A smoke film can be a concern to those who frequently burn a candle indoors and is also referred to as ghosting, carbon tracking, carbon tracing. Smoke can be produced when a candle does not burn the wax fuel completely. A scented candle can be a source of candle smoke deposits. Trimming candle wicks to about 6 millimeters (¼ in) or shorter is recommended to keep smoking at a minimum. A flickering flame will produce more smoke, therefore a candle should be burned in an area free from drafts. (See for more details.)
Additional debate on the use of wax in a candle exist on what is "natural". Proponents of the soy wax candle will note the material is biodegradable and "all natural". However, most soy beans that result in the ultimate manufacture of soy wax in the candle are genetically modified. Paraffin wax, as used in candle making, is also biodegradable. It also often meets the United States' Food and Drug Administration criteria for use in foods and in contact with food.
Decorative candle holders, especially those shaped as a pedestal, are called candlesticks; if multiple candle tapers are held, the term candelabrum is also used. The root form of chandelier is from the word for candle, but now usually refers to an electric fixture. The word chandelier is sometimes now used to describe a hanging fixture designed to hold multiple tapers.
Many candle holders use a friction-tight socket to keep the candle upright. In this case, a candle that is slightly too wide will not fit in the holder, and a candle that is slightly too narrow will wobble. Any candle that is too large can be trimmed to fit with a knife; a candle that is too small can be fitted with aluminum foil. Traditionally, the candle and candle holders were made in the same place, so they were appropriately sized, but international trade has combined the modern candle with existing holders, which makes the ill-fitting candle more common. This friction tight socket is only needed for the federals and the tapers. For tea light candles, there are a variety of candle holders, including small glass holders and elaborate multi candle stands. The same is true for votives. Wall sconces are available for tea light and votive candles. For pillar type candles, the assortment of candle holders is broad. A fireproof plate, such as a glass plate or small mirror, is a candle holder for a pillar style candle. A pedestal of any kind, with the appropriate sized fire proof top, is another option. A large glass bowl with a large flat bottom and tall mostly vertical curved sides is called a hurricane. The pillar style candle is placed at the bottom center of the hurricane. A hurricane on a pedestal is sometimes sold as a unit.
The liquid wax is hot and can cause skin burns, but the amount and temperature are generally rather limited and the burns are seldom serious. The best way to avoid getting burned from splashed wax is to use a candle snuffer instead of blowing on the flame. A candle snuffer is usually a small metal cup on the end of a long handle. When placed over the flame the oxygen supply is cut off. They were used daily when the candle was the main source of lighting a home, before electric lights were available.
Glass candle holders are sometimes cracked by thermal shock from the candle flame, particularly when the candle burns down to the end.
A former worry regarding the safety of candles was that a lead core was used in the wicks to keep them upright in container candles. Without a stiff core, the wicks of a container candle could sag and drown in the deep wax pool. Concerns rose that the lead in these wicks would vaporize during the burning process, releasing lead vapors — a known health and developmental hazard. Lead core wicks have not been common since the 1970s. Imported candles may still be found to have some lead core wicks. Today, most metal-cored wicks use zinc or a zinc alloy, which has become the industry standard. Wicks made from specially treated paper and cotton are also available.
The hottest part of the flame is just above the very dull blue part to one side of the flame, at the base. At this point, the flame is at 1,400°C.