from The American Heritage® Dictionary of the English Language, 4th Edition

  • n. The quality or property of being efficient.
  • n. The degree to which this quality is exercised: The program was implemented with great efficiency and speed.
  • n. The ratio of the effective or useful output to the total input in any system.
  • n. The ratio of the energy delivered by a machine to the energy supplied for its operation.
  • n. An efficiency apartment.

from Wiktionary, Creative Commons Attribution/Share-Alike License

  • n. The extent to which time is well used for the intended task.
  • n. The quality of producing an effect or effects.
  • n. The extent to which a resource, such as electricity, is used for the intended purpose; the ratio of useful work to energy expended.
  • n. A one-room apartment.

from The Century Dictionary and Cyclopedia

  • n. The quality of being efficient; effectual agency; competent power; the quality or power of producing desired or intended effects.
  • n. Specifically— The state of being able or competent; the state of possessing or having acquired adequate knowledge or skill in any art, profession, or duty: as, by patient perseverance he has attained a high degree of efficiency.
  • n. In mech., the ratio of the useful work performed by a prime motor to the energy expended. Synonyms Efficacy, etc. See effectiveness.
  • n. Angström's method. Another method of measuring the radiant efficiency of a source of light is due to Knut Ångström. An opaque screen is mounted in such a position as to cut off all rays lying beyond the red end of the visible spectrum, and the remaining radiation is assembled upon the face of a bolometer by means of a cylindrical lens. The ratio of this quantity to the total radiation, measured by the same instrument, gives the radiant efficiency of the source of light. The radiant efficiency of such sources of light as have been measured by the two methods thus described is given in the following table. The values obtained by the integration of the energy-curves and by Ångström's method are marked respectively L and A.
  • n. While other sources of light have not as yet been measured by these methods, their relative efficiencies are approximately known, and by comparison with the above data we know that the radiant efficiency of ordinary oil- and gas-flames is about .01, that of the glow-lamp from .01 to .03, and that of the electric arc from .04 to .08. Gross efficiency. The term efficiency is likewise used to express the ratio of the energy in light-giving form developed in unit time by a source to the energy of combustion of the fuel which it is necessary to consume in order to maintain the source during that time. The efficiency thus defined takes into account the total heat-losses in the production of light. In the case of the flames of candles and of oil-lamps the heat lost by convection and conduction is very large compared with the total radiation from the flame. In the case of gas-flames the heat of combustion of the coal necessary to produce the gas to maintain the flame, as compared with the luminous energy emitted by the flame, gives the gross efficiency. In computing the gross efficiency of electric lights the heat of combustion of the fuel used to generate the current supplied to the lamps or the equivalent amount of energy, whatever be its source, is to be taken. In the case of a steam-plant for electric lighting the losses by dissipation of heat in the boiler, engine, dynamo, and lead-wires, together with the loss by convection and conduction in the electric lamp itself, all enter into the computation of the gross efficiency. Whatever process for the production of light may be employed, the amount of energy dissipated for the purpose of obtaining luminous radiation is very great, and the gross efficiency of luminous flames used in lighting ranges from .001 to .002, while the gross efficiency of electric lamps under the best existing conditions for the production of power is little if any above these figures. Electric efficiency. It is convenient in the case of the electric light to express the efficiency in watts per candle—a method not comparable with the energy-ratio defined above, but useful for the comparison of the various types of lamp used in electric lighting. The electric efficiency of the ordinary lamp ranges between four watts per candle and three watts per candle, according to the temperature of the filament, that of the arc-light from two watts per candle to one watt per candle (mean spherical candle-power), while the efficiency of the Nernst lamp is intermediate between that of the arc and the glow-lamp.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

  • n. the ratio of the output to the input of any system
  • n. skillfulness in avoiding wasted time and effort


Latin efficientia (Wiktionary)



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  • Let's hope this car is better.

    August 4, 2009

  • "This article documents and analyzes the changes in fuel efficiency of vehicles on US roads between 1923 and 2006. Information about distances driven and fuel consumed was used to calculate the on-the-road fuel efficiency of the overall fleet and of different classes of vehicles. The overall fleet fuel efficiency decreased from 14 mpg in 1923 to 11.9 mpg in 1973. Starting in 1974, efficiency increased rapidly to 16.9 mpg in 1991. Thereafter, improvements have been small, with efficiency reaching 17.2 mpg in 2006."
    - Sivak, M. & Tsimhoni, O., Fuel efficiency of vehicles on US roads: 1923–2006.

    August 4, 2009