Energy conversion efficiency (η) is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The input, as well as the useful output may be chemical, electric power, mechanical work, light (radiation), or heat.

Energy conversion efficiency depends on the utility of the output. All or part of the heat produced by a heat exchanger, for example, is the desired output of a thermodynamic cycle. Energy converter is an example of an energy transformation. For example a light bulb falls into the categories energy converter. Even though the definition includes the notion of usefulness, is considered a technical or physical term. Goal or mission oriented terms include effectiveness and efficacy. Generally, energy conversion efficiency is a dimensionless number between 0 and 1.0, or 0% to 100%. Efficiencies may not exceed 100%, eg, for a perpetual motion machine. However, other measures that can exceed 1.0 are used for heat pumps and other devices that move heat rather than convert it. When talking about the efficiency of heat engines and power stations the convention should be stated, ie, HHV (Gross Heating Value, etc.) or LCV (aka net heating value), and whether gross output (at the generator terminals) or net output (at the power station fence) are being considered. The two are separate but both must be stated. Failure to do so causes endless confusion. Related, more specific terms include

In Europe, the use of fuel oil is of a higher fuel efficiency (LHV) than that of fuel, the definition of which fuel is used during fuel combustion (oxidation), remains gaseous, and is not condensed to liquid water. so the latent heat of vaporization of that water is not usable. Using the LHV, a condensing boiler can achieve a “heating efficiency” in excess of 100% (which does not violate the first law of thermodynamics as long as the LHV convention is understood, but does cause confusion). This is because the apparatus recovers part of the heat of vaporization, which is not included in the definition of the lower heating value of fuel. In the US and elsewhere, the higher heating value (HHV) is used, which includes the latent heat for condensing the water vapor,

In optical systems such as lighting and lasers, the energy conversion efficiency is often referred to as a wall-plug efficiency. The wall-plug efficiency is the measure of radiative-energy output, in watts (joules per second), for the total of the electrical input-energy in watts. The output-energy is usually measured in terms of absolute irradiance and the wall-plug efficiency is given as a percentage of the total input-energy, with the inverse percentage representing the losses. The wall-plug efficiency differs from the luminous efficiency in that wall-plug efficiency describes the direct output / input conversion of energy (the amount of work that can be performed) how well it can illuminate a space). Instead of using watts, the power of a light source to produce wavelengths proportional to human perception is measured in lumens. The human eye is most sensitive to wavelengths of 555 nanometers (greenish-yellow) but the sensitivity decreases dramatically to that side of this wavelength, following a Gaussian power-curve and dropping to zero sensitivity at the red and violet ends of the spectrum. To to the…………………… Yellow and green, for example, make up more than 50% of what the eye perceives as being white, even though in terms of radiant energy white-light is made from equal parts of all colors (ie: a 5 mw green laser appears brighter than a 5 mw red laser, yet the red laser stands out better against a white background). Therefore, the radiant intensity of a light source may be much greater than its luminous intensity, meaning that the source emits more energy than the eye can use. Likewise, the lamp’s wall-plug efficiency is usually greater than its luminous efficiency. The effectiveness of a light source to convert electrical energy into visible light, in the light of the light of the human eye, is referred to as luminous efficacy, which is measured in units of lumens per watt (lm / w) of electrical input -Energy. Characterized by efficiency, which is a unit of measurement, Therefore, The luminous efficiency of a light source is the percentage of luminous efficacy for the theoretical-maximum efficacy at a specific wavelength. The amount of energy carried by a photon of light is determined by its wavelength. In lumens, this energy is offset by the eye’s sensitivity to the selected wavelengths. For example, a green laser pointer can be greater than 30 times the apparent brightness of a red pointer of the same power output. At 555 nm in wavelength, 1 watt of radiant energy is equivalent to 685 lumens, thus a monochromatic light source at this wavelength, with a luminous efficacy of 685 lm / w, has a luminous efficiency of 100%. The theoretical-maximum efficiency lowers for wavelengths at 555 nm. For example, low-pressure sodium lamps produce monochromatic light at 589 nm with a luminous efficacy of 200 lm / w, which is the highest of any lamp. The theoretical-maximum efficacy at that wavelength is 525 lm / w, so the lamp has a luminous efficiency of 38.1%. Because the lamp is monochromatic, the luminous efficiency nearly matches the wall-plug efficiency of <40%. Calculations for luminous efficiency become more complex for lamps that produce white light or a mixture of spectral lines. Fluorescent lamps have higher wall-plug efficiencies than low-pressure sodium lamps, but only have half the luminous efficacy of ~ 100 lm / w, thus the luminous efficiency of fluorescent is lower than sodium lamps. A xenon flashtube has a typical wall-plug efficiency of 50–70%, exceeding that of most other forms of lighting. Because the flashtube emits large amounts of infrared and ultraviolet radiation, only a portion of the energy output is used by the eye. The luminous efficiency is typically around 50 lm / w. However, not all applications for lighting involve the human eye nor are they restricted to visible wavelengths. For laser pumping, the efficacy is not related to the human eye so it is not called “luminous” efficacy, but rather simply “efficacy” as it relates to the absorption lines of the laser medium. Krypton flashtubes are often chosen for pumping, even though their wall-plug efficiency is typically only ~ 40%. Krypton’s spectral lines of neodymium-doped crystal, thus the efficacy of krypton for this purpose is much higher than xenon; able to produce up to the laser output for the same electrical input. All of these terms refer to the amount of energy and lumens as they exit the light source, disregarding any losses that might occur within the lighting fixture or subsequent output optics. Luminaire efficiency refers to the total lumen output of the fixture for the lamp output. With the exception of a few light sources, such as incandescent light bulbs, most light sources have multiple stages of energy conversion between the “wall plug” (electrical input point, which may include batteries, direct wiring, or other sources) and the final light-output, with each stage producing a loss. Low-pressure sodium lamps are widely used in the electrical energy market, and are usually used in the ballast. Similarly, fluorescent lamps also use electronic ballast (electronic efficiency). Electricity is then converted into light energy by the electrical arc (electrode efficiency and discharge efficiency). The light is then transferred to a fluorescent coating that only absorbs suitable wavelengths, with some losses of those wavelengths due to reflection off and transmission through the coating (transfer efficiency). The number of photons absorbed by the coating will not match the number then reemitted as fluorescence (quantum efficiency). Finally, due to the phenomenon of the Stokes shift, the reemitted photons will-have to go short wavelength (THUS lower energy) than the absorbed photon (fluorescence efficiency). In very similar fashion, lasers aussi Many internship experience of conversion entre les wall plug and the output aperture. The terms “wall-plug efficiency” or “energy conversion efficiency”