Lux[1](lux, legal symbol lx) isillumination(luminance).The object that is evenly illuminated by light is obtained on an area of 1 square meterLuminous fluxYes 1LumenIts illuminance is 1 lux.The illumination suitable for reading and sewing is about 60-100 lux.[5]
Lux is the international unit of illuminance (SI), also known as meter candle.The object that is evenly illuminated by light is obtained on an area of 1 square meterLuminous fluxWhen it is 1 lumen, its illuminance is 1 lux.It can be labeled as Le [x], or Le for short.Lux in English, or lx in short[2]。
Lux is the unit of derivation, which is derived from lumens (lm).Lumens are measured in standard unitsCandela(cd) Lead out.
Illumination is a reflectionLight intensityA physical quantity of, its physical meaning is the luminous flux on the unit area. The unit of illuminance is the number of lumens (lm) per square meter, and its unit is lux (or lx), that is, 1lux=1lm/mtwo[3]。
relationship
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1lux=1lm/m2=1cd × sr/m2
Lumen
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Lumen, the unit of luminous flux.For a point light source with luminous intensity of 1 candela (cd), the luminous flux emitted within the unit solid angle (1 spherical degree) is "1 lumen", which is abbreviated as lm.
In short, the so-called lumen refers to the brightness of a candle at a distance of one meter (1 meter=1 meter).An ordinary 40 watt incandescent bulb has a luminous efficiency of about 10 lumens per watt, so it can emit 400 lumens of light.The luminous flux of a 40 watt incandescent lamp is 340 lumens at 220 volts.Luminous flux refers to the ability of light source radiation to produce visual response in unit time. Its unit is lumen, also called brightness.The projector represents the luminous flux in ANSI lumens,ANSI lumen is the standard for measuring the luminous flux of the projector developed by the American National Institute for Standardization. It measures the illuminance of each point on the nine intersections of the screen "Tian", multiplies the area, and then calculates the average value of the nine points, which is the ANSI lumen of the projector. The higher the lumen value, the brighter it is. The higher the brightness, the less need to turn off the light during projection.ANSI is American National Standards Institute（National Bureau of Standards）Abbreviation of.Similarly, for the light source, this quantity describes the size of the total amount of light emitted by the light source and is equivalent to the light power.The greater the luminous flux of the light source, the more light is emitted.For isotropic light (that is, the light from the light source emits at the same density in all directions), F=4 π * l, that is, if 1 of the light source is 1 cd, the total luminous flux is 4x=12.56lm. Compared with the mechanical unit, the luminous flux is equivalent to pressure, and the luminous intensity is equivalent to pressure.To make the irradiated point look brighter, we need not only to increase the luminous flux, but also to increase the means of convergence, which is actually to reduce the area, so that we can get greater intensity.You should know that the luminous flux is also an artificial quantity, which may be different from other animals, and even less natural, because this definition is completely based on the response of the human eye to light.The human eye's perception of light of different colors is different, which determines the conversion relationship between luminous flux and optical power.For the yellow green light at 555nm, which is the most sensitive light to the human eye, 1W=683lm, that is to say, the power of 1W is all converted into light at 555nm, which is 683 lumens.This is the maximum light conversion efficiency and the calibration value, because the human eye is most sensitive to 555nm light.For other colors of light, such as 650nm red, 1W light is only equivalent to 73 lumens, which is because the human eye is not sensitive to red light.For white light, it depends, because many light with different spectral structures are white.For example, the white light of LED, the white light on TV and sunlight are very different, with different spectra.As for the luminous efficiency of the electric light source, it is another related topic, that is, how much luminous flux can 1W electric power be converted into.If all the light is converted to 555nm, it is 683 lumens per watt.However, if one half is converted to 555nm light and the other half is lost in heat, the efficiency is 341.5 lumens per watt.It is very good if the incandescent lamp can reach 1W=20Im, and the rest will become heat or infrared.Measuring the luminous flux of an irregular illuminant requires an integrating sphere, which is professional and complex.
Luminous flux and lumen
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The light energy emitted by the light source radiates in all directions. The light energy passing through a certain area in unit time is called the radiant energy flux passing through this area.The frequency of each color light is different, and the mosquito sensitivity of the eyes to each color light is also different. Even if the radiant energy flux of each color light is equal, it cannot produce the same brightness visually. Among all colors of light, yellow and green light can stimulate the greatest brightness.If the green light is used as the level, and its luminous flux is equal to the radiant energy flux, then for other colored lights, the ability to stimulate a bright feeling is smaller than the green light, and the luminous flux is also smaller than the radiant energy flux.The unit of luminous flux is lumen, which is transliteration of English lumen. It is abbreviated as Im absolute black body at platinum solidification temperature, ranging from 5.305 * 10 ³ cm ²;The luminous flux radiated from the area is 1m.To show the relationship between light intensity and luminous flux, the luminous flux emitted by a point light source with luminous intensity of 1 candela is 1 lumen within the unit solid angle (1 spherical degree).The output luminous flux of a 40W fluorescent lamp is about 2100 lumens[3]。
Illumination and lux
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The illuminance can be measured directly with an illuminometer.The unit of illuminance is lux, which is a transliteration of lux in English, and can also be written as x.When the luminous flux of an object evenly illuminated by light is 1 lumen over an area of 1 square meter, its illuminance is 1 lux.Sometimes, in order to make full use of the light source, a reflector is often attached to the light source, so that more luminous flux can be obtained in some directions to increase the illuminance on the illuminated surface.For example, car headlights, flashlights, photography lights, etc.
Site/Environment
Illuminance
night
0.001-0.02lux
moonlit night
0.02~0.3lux
Street lamp at night
0. 1lux
Indoor fluorescent lamp
100lux
TV studio
1000lux
Illumination required for reading books
50-60lux
Reference source:[4]
Illuminance standard
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Illuminance is the luminous flux received by the surface of the object to be illuminated on the unit area.The illuminance is generally expressed as "foot candles".1 foot candle refers to the illuminance generated by a light source with a luminous intensity of 1 candle on a vertical plane one foot away from the light source and one square foot in area.The average illuminance of foot candles is 1 lumen per square foot, so it can be written as 1 lumen per square foot.The illuminance can also be expressed in "meter candles", called "lux", that is, an area of one square meter is illuminated by candles one meter away.The illuminance of a light source with the same intensity on the object is related to its distance from the light source, so the illuminance of foot candles is greater than that of meter candles.Illumination of 1 foot candle=10.76 meter candle;The illuminance of 1 meter candle=0.093 foot candle illuminance is a unit that reflects the light intensity. Its physical meaning is the luminous flux that shines on the unit area. The unit of illuminance is the number of lumens (Lm) per square meter, also called Lux: 1Lwx=1Lm square meter. In the above formula,Lm is the unit of luminous flux, which is defined as the amount of light radiated by the 160 square meter surface area of pure platinum in a solid angle of 1 spherical degree at the melting temperature (about 1770 ℃).General situation: 100000lx in summer sunshine;10000lx outdoor in cloudy days;100lx for indoor fluorescent lamp;300lx from the table top 60cm away from the 60W desk lamp;1000lx for TV studio;10lx indoors at dusk;0.1lx for street light at night;Candlelight (20cm away) 10~15lx.The illumination at 1m under 40W incandescent lamp is about 30im;After adding a porcelain umbrella cover, the illuminance will increase to 731k;The outdoor illuminance at noon on cloudy days is 8000~20000k;The outdoor illuminance in sunny noon can be as high as 8000~012000w[3]。
