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The term candlepower was originally defined in England by the Metropolitan Gas Act of 1860 as the light produced by a pure spermaceti candle weighing one sixth of a pound and burning at a rate of 120 grains per hour. Spermaceti is found in the head of Sperm Whales, and once was used to make high quality candles.At this time the French standard of light was based upon the illumination from a Carcel Burner. The unit was defined as that illumination emanating from a lamp burning pure colza oil (obtained from the seed of the plant Brassica campestris) at a defined rate. It was accepted that ten Standard Candles were about equal to one Carcel burner.In 1909 a meeting took place to come up with an international standard. It was attended by representatives of the Laboratoire Central de l’Electricité (France), the National Physical Laboratory (UK), the Bureau of Standards (United States) and the Physikalische Technische Reichsanstalt (Germany). The majority redefined the candle in term of an electric lamp with a carbon filament. The Germans, however, dissented and decided to use a definition equal to 9⁄10ths of the output of a Hefner lamp.In 1921, the Commission Internationale de l’Eclairage (International Commission for Illumination, commonly referred to as the CIE) redefined the international candle again in terms of a carbon filament incandescent lamp.In 1937, the international candle was redefined again against the luminous intensity of a blackbody at the freezing point of liquid platinum which was to be 58.9 international candles per square centimeter.Since 1948 the term candlepower was replaced by the international unit (SI) known as the candela. One old candlepower unit is about 0.981 candela. Less scientifically, modern candlepower now equates directly (1:1) to the number of candelas -- an implicit increase from its old value.
If the source emits light uniformly in all directions, the flux can be found by multiplying the intensity by 4π: a uniform 1 candela source emits 12.6 lumens.
Comparison of efficiency by wattage (120 Volt lamps)Power (W) Output (lm) Efficiency (lm/W)40 500 12.565 1000 15.070 1100 15.7
"It is not the wax that burns (generates energy) but the wick. The wax is more of a moderator to ensure it does not burn too fast."Nonsense, just for a start there were oil lamps with asbestos wicks.
What is 12.6 lumens in watts?
It is not the wax that burns (generates energy) but the wick. The wax is more of a moderator to ensure it does not burn too fast.
QuoteIt is not the wax that burns (generates energy) but the wick. The wax is more of a moderator to ensure it does not burn too fast.Where did you get that idea from?
Quote from: Karen W. on 20/01/2008 21:31:44What is 12.6 lumens in watts?A lumen is a measure of perceived light falling on a given area.Wattage is a measure of power. In the calculation above, I looked at the amount of power required to generate the given amount of light using an incandescent light bulb radiating equally in all directions. This makes assumptions about the inefficiencies of the incandescent light bulb (even with incandescent bulbs, higher rated bulbs were more efficient at emitting light for a given unit of power). A different assumption for those inefficiencies (e.g. if one assumed a compact fluorescent light bulb, rather than an incandescent light bulb, and the correlation would be different).Another assumption here is with the way that the human eye absorbs light (since it is perceived light intensity that is measured), so the amount of light for a given wattage would be perceived differently for different species of animal (and may even be slightly different for different individual human beings).Another way of looking at the power is by looking at the power actually contained in light (this is often quoted for sunlight, since this figure is used to look at the potential power available for solar energy converters, but the figures are not usually adapted for human perception, which is not evenly distributed across the spectrum).
When the average candle burns, how does one calculate how much heat energy it is producing per weight of wax, and what is the equivalent light output, in watts, from an electric lightbulb?Chris
Hmm, having recently bought a solar powered robot, I was wondering (what with it being winter) whether it would be possible to use the photons from a candle to power the robot. The instructions suggest a 50W halogen bulb can be used on cloudy/wintry days, but I was going to try candles instead (plus some mirrors) instead.What do you reckon as to my chance of success?