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Luminous efficacy can be normalized by the maximum possible luminous efficacy to a dimensionless quantity called luminous efficiency.The distinction between efficacy and efficiency is not always carefully maintained in published sources, so it is not uncommon to see "efficiencies" expressed in lumens per watt, or "efficacies" expressed as a percentage.
The same 1,000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux. In equation form, 1 lx = 1 lm/m 2. A source radiating a power of one watt of light in the color for which the eye is most efficient (a wavelength of 555 nm, in the green region of the optical spectrum) has luminous flux of 683 lumens.
Power ratings are usually given in watts for real power and volt-amperes for apparent power, although for devices intended for use in large power systems, both may be given in a per-unit system. Cables are usually rated by giving their maximum voltage and their ampacity . [ 4 ]
In a climate-controlled environment, like a home or office, heat generated by appliances may reduce heating costs or increase air conditioning costs. Impedance bridging connections have a load impedance much larger than the source, which helps transfer voltage signals at high electrical efficiency.
The sensitivity of the human eye to various wavelengths. Assuming each wavelength equals 1 watt of radiant energy, only the center wavelength is perceived as 683 candelas (1 watt of luminous energy), equaling 683 lumens. The vertical colored-lines represent the 589 (yellow) sodium line, and popular 532 nm (green), 671 nm (red), 473 nm (blue ...
The luminous efficacy of a typical CFL is 50–70 lumens per watt (lm/W) and that of a typical incandescent lamp is 10–17 lm/W. [38] Compared to a theoretical 100%-efficient lamp ( 680 lm/W ), CFL lamps have lighting efficiency ranges of 7–10%, [ 39 ] versus 1.5–2.5% [ 40 ] for incandescents.
A typical 100 watt incandescent lamp has an efficiency of no more than 17.5 lumens per watt (l/W) and will therefore produce 1750 lumens at its rated voltage. A typical modern LED lamp has an efficiency of about 150 lumens per watt, and therefore requires no more than 12 watts for the same light output.
As of 2010 some LED lamps replaced higher wattage bulbs; for example, one manufacturer claimed a 16-watt LED lamp was as bright as a 150 W halogen lamp. [71] A standard general-purpose incandescent bulb emits light at an efficacy of about 14 to 17 lm/W depending on its size and voltage. (Efficacy of incandescent lamps designed for 230 V ...