發光效能

發光效率 是一个光源的参数。他是光通量與功率的比值，依照文字來源此功率指的是光源輸出的輻射通量，或者是提供光源的電能 ，前者的定義有時叫輻射發光效率，後者稱電源發光效率。 電源發光效率為一種：測量電能提供光源發出可見光的效率。 輻射發光效率描述：光源提供可見光的效率，也就是光通量對輻射通量的比值。 因人眼的結構，並非所有波長的光能見度都一樣。紅外光和紫外光的光譜對於發光效率不造成影響。光源的發光效率与光源把能量转化为电磁辐射的能力以及人眼感知所发出的辐射的能力有关。

效率的不同表示方法

在一些單位制中, 光通量和輻射通量的單位是一樣的, 這時的輻射發光效率無法被量化, 在這種情況下發光效率可以被用百分比來表示。一個普遍的做法是選擇最大的效率, 683 lm/W, 作為發光效率100%的標準。在絕大部份例子中採用百分比表示和lm/W來表示沒有特殊的限制。

輻射發光效率

定義

The response of a typical human eye to light, as standardized by the CIE in 1924. The horizontal axis is wavelength in nm

波長位於可見光譜以外的輻射對於照明來說是沒有用的, 因為它們無法被人眼感知。即使在可見光譜的波段里, 人眼對於一些光的敏感度會高於另外一些光, 眼睛的這種特性可由視見函數所表示。它表示了一個標準觀測者在亮度比較高的環境(明視覺)條件下所表現出來的觀測能力。同樣我們也可以定義在比較暗的環境(暗視覺)條件下的函數曲綫。如果沒有特別指出的話，通常都是指的明視覺的視見函數。

Luminous efficacy of radiation measures the fraction of electromagnetic power which is useful for lighting. It is obtained by dividing the luminous flux by the radiant flux. Light with wavelengths outside the visible spectrum reduces luminous efficacy, because it contributes to the radiant flux while the luminous flux of such light is zero. Wavelengths near the peak of the eye's response contribute more strongly than those near the edges.

In SI, luminous efficacy has units of lumens per watt (lm/W). Photopic luminous efficacy of radiation has a maximum possible value of 683 lm/W, for the case of monochromatic light at a wavelength of 555 nm (green). Scotopic luminous efficacy of radiation reaches a maximum of 1700 lm/W for narrowband light of wavelength 507 nm.

Mathematical definition

The dimensionless luminous efficiency measures the integrated fraction of the radiant power that contributes to its luminous properties as evaluated by means of the standard luminosity function. The luminous coefficient is

${\frac {\int _{0}^{\infty }y_{\lambda }J_{\lambda }d\lambda }{\int _{0}^{\infty }J_{\lambda }d\lambda }},$

where

y_λ is the standard luminosity function,

J_λ is the spectral power distribution of the radiant intensity.

The luminous coefficient is unity for a narrow band of wavelengths at 555 nanometres.

Note that $\int _{0}^{\infty }y_{\lambda }J_{\lambda }d\lambda$ is an inner product between $y_{\lambda }$ and $J_{\lambda }$ and that $\int _{0}^{\infty }J_{\lambda }d\lambda$ is the one-norm of $J_{\lambda }$.

例子

Spectral radiance of a black body. Energy outside the visible wavelength range (~380–750 nm, shown by grey dotted lines) reduces the luminous efficiency.

File:Blackbody efficiency.png

Type	Luminous efficacy of radiation (lm/W)	Luminous efficiency
Class M star (Antares, Betelgeuse), 3000 K	30	4%
ideal black-body radiator at 4000 K	47.5	7.0%
Class G star (Sun, Capella), 5800 K	80	12%
ideal black-body radiator at 7000 K	95	14%
ideal 5800 K black-body, truncated to 400–700 nm (ideal "white" source)	251	37%
ideal monochromatic 555 nm source	683	100%

Lighting efficiency

Artificial light sources are usually evaluated in terms of luminous efficacy of a source, also sometimes called overall luminous efficacy. This is the ratio between the total luminous flux emitted by a device and the total amount of input power (electrical, etc.) it consumes. It is also sometimes referred to as the wall-plug luminous efficacy or simply wall-plug efficacy. The overall luminous efficacy is a measure of the efficiency of the device with the output adjusted to account for the spectral response curve (the “luminosity function”). When expressed in dimensionless form (for example, as a fraction of the maximum possible luminous efficacy), this value may be called overall luminous efficiency, wall-plug luminous efficiency, or simply the lighting efficiency.

The main difference between the luminous efficacy of radiation and the luminous efficacy of a source is that the latter accounts for input energy that is lost as heat or otherwise exits the source as something other than electromagnetic radiation. Luminous efficacy of radiation is a property of the radiation emitted by a source. Luminous efficacy of a source is a property of the source as a whole.

Examples

The following table lists luminous efficacy of a source and efficiency for various light sources:

Category	Type	Overall luminous efficacy (lm/W)	Overall luminous efficiency
Combustion	candle	0.3	0.04%
	gas mantle	1–2	0.15–0.3%
Incandescent	100–200 W tungsten incandescent (230 V)	13.8–15.2	2.0–2.2%
	100–200–500 W tungsten glass halogen (230 V)	16.7–17.6–19.8	2.4–2.6–2.9%
	5–40–100 W tungsten incandescent (120 V)	5–12.6–17.5	0.7–1.8–2.6%
	2.6 W tungsten glass halogen (5.2 V)	19.2	2.8%
	tungsten quartz halogen (12–24 V)	24	3.5%
	photographic and projection lamps	35	5.1%
Light-emitting diode	white LED (raw, without power supply)	4.5–150	0.66–22.0%
	4.1 W LED screw base lamp (120 V)	58.5–82.9	8.6–12.1%
	5.4 W LED screw base lamp (100 V 50/60Hz)	101.9	14.9%
	6.9 W LED screw base lamp (120 V)	55.1–81.9	8.1–12.0%
	7 W LED PAR20 (120 V)	28.6	4.2%
	8.7 W LED screw base lamp (120 V)	69.0–93.1	10.1–13.6%
	Theoretical limit	260.0–300.0	38.1–43.9%
Arc lamp	xenon arc lamp	30–50	4.4–7.3%
	mercury-xenon arc lamp	50–55	7.3–8.0%
Fluorescent	T12 tube with magnetic ballast	60	9%
	9–32 W compact fluorescent	46–75	8–11.45%
	T8 tube with electronic ballast	80–100	12–15%
	PL-S 11W U-tube with traditional ballast	82	12%
	T5 tube	70–104.2	10–15.63%
	Spiral tube with electronic ballast	114-124.3	15–18%
Gas discharge	1400 W sulfur lamp	100	15%
	metal halide lamp	65–115	9.5–17%
	high pressure sodium lamp	85–150	12–22%
	low pressure sodium lamp	100–200	15–29%
Cathodoluminescence	electron stimulated luminescence	30	5%
Ideal sources	Truncated 5800 K blackbody	251	37%
	Green light at 555 nm (maximum possible luminous efficacy)	683.002	100%

Sources that depend on thermal emission from a solid filament, such as incandescent light bulbs, tend to have low overall efficacy compared to an ideal blackbody source because, as explained by Donald L. Klipstein, “An ideal thermal radiator produces visible light most efficiently at temperatures around 6300 °C (6600 K or 11,500 °F). Even at this high temperature, a lot of the radiation is either infrared or ultraviolet, and the theoretical luminous [efficacy] is 95 lumens per watt. Of course, nothing known to any humans is solid and usable as a light bulb filament at temperatures anywhere close to this. The surface of the sun is not quite that hot.” At temperatures where the tungsten filament of an ordinary light bulb remains solid (below 3683 kelvins), most of its emission is in the infrared.

參看

• 光污染

外部連結

• Hyperphysics has these graphs of efficacy that do not quite comply with the standard definition
• Energy Efficient Light Bulbs
• Other Power
• CIPCO Energy Library