A candle is a light source usually consisting of an internal wick which rises through the center of a column of solid fuel. Prior to the mid 19th century, the majority of candles were tallow (a byproduct of beef fat rendering). The fuel now is nearly always some form of wax, with paraffin wax being the most common. Soy and vegetable-based candles are also available, however.
Prior to the candle being ignited, the wick is saturated with the fuel in its solid form. The heat of the match or other flame being used to light the candle first melts and then vaporizes a small amount of the fuel. Once vaporized, the fuel combines with oxygen in the atmosphere to form a flame. This flame then 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, hotter 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 soot being oxidized to form carbon dioxide.
As the mass of the solid fuel is melted and consumed, the candle grows shorter. Portions of the wick that are not evaporating the liquid fuel are, ideally, consumed in the flame, limiting the exposed length of the wick and keeping the temperature and rate of fuel consumption even. Some wicks required manual trimming with scissors or a wick trimmer for even burning, but these are rarely found in modern candles.
Candles were developed independently in many countries. The Egyptians and Cretans made candles from beeswax, as early as 3000 BC. Early candles were made from various forms of natural fat, tallow, and wax. In the 18th century, spermaceti, an oil produced by the sperm whale, was used to produce superior candles. 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 high-quality, odorless candles that burned reasonably cleanly. The industry was devastated soon after, however, by the distillation of kerosene (confusingly also called paraffin oil or just paraffin). This excellent fuel for lamps relegated candles to their current status as primarily decorative items.
Today, candles are usually used for their aesthetic value, particularly to set a soft, warm, or romantic ambience, and for emergency lighting during electrical power failures. Scented candles are common in aromatherapy. Small candles are often placed on birthday cakes.
Candles were traditionally used to light up Christmas trees before the advent of electric lights. They are still, even today, commonly used to decorate Christmas trees in Denmark and other European countries. They are also used in Advent wreaths.
In Sweden (and other Scandinavian countries), St. Lucia Day is celebrated on December 13 with the crowning of a young girl with a ring of candles.
In the days leading to Christmas some people burn a candle a set amount to represent each day, as marked on the candle. Candles used in this way are called Advent candles, although this term is also used to refer to the candles which decorate 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 roughly one candela.
It is commonly believed that candles made of beeswax and/or soy burn more cleanly than petroleum based paraffin waxes. However highly-refined paraffin wax will 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 volatile compounds, particulates, and soot. Any of these will increase the amount of particulates put into the air by any candle regardless of construction materials. The cleanest burning candles will therefore be unscented, undyed, and well constructed candles burning in a draft free area.
Black Soot Deposition (BSD) can be a concern to those who frequently burn candles indoors and is also referred to as ghosting, carbon tracking, carbon tracing, and dirty house syndrome. Soot can be produced when candles do not burn the wax fuel completely. Scented candles are the major source of candle soot deposition. Trimming candle wicks to one fourth of an inch is recommended to keep soot production at a minimum. A flickering flame will produce more soot, therefore candles should be burned in an area free from drafts. (see http://web.ksl.com/dump/news/cc/series/candepa.htm for more details)
Decorative candle holders, especially those shaped as a pedestal, are called candlesticks; if multiple candles 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 candelier is sometimes now used to describe a hanging fixture designed to hold multiple candles.
Many candle holders use a friction-tight socket to keep the candles 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. Traditionally, candles and candle holders were made in the same place, so they were appropriately sized, but international trade has combined modern candles with existing holders, which makes ill-fitting candles more common.
Electric candle warmers are now being sold so that candle wax can be melted to release the fragrance without requiring an open flame.
A former worry regarding the safety of candles was that a lead core is used in the wicks in order to keep the wicks upright in container candles. Without a stiff core, the wicks of container candles would sag and drown in the deep wax pool. Concerns rose that the lead in these wicks would vaporize during the burning process, releasing lead vapours - a known health and developmental hazard. Lead core wicks have not been common since the 1970s: some candles may still be found to have lead core wicks, but these are extremely rare. Most metal-cored wicks use zinc or a zinc alloy. Wicks made from specially treated paper and cotton are also available. These wicks eliminate the need for metal in the wick.
شمعة Свещ Kerze Vela (iluminación) Kandelo Bougie Candea Lilin Candela (illuminazione) נר Lilin Kaars ろうそく Levande lys Świeca Vela (iluminação) Свеча Candle Sveča Свећа Kynttilä Stearinljus 蜡烛