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Wednesday, November 25, 2020

What is Luminaire Luminous Flux (Φ) ?

Light intensity is a physical term that refers to the luminous flux of visible light received per unit area . Referred to as illuminance , the unit is Lux (Lux or lx). It is used to indicate the intensity of light and the amount of illumination of the surface area of the object.

In photometry , luminance is the density of luminous intensity in a specified direction , but it is often misunderstood as illuminance . The international unit of luminosity is the candle light per square meter (called candela in Mainland China, Hong Kong and Macau ).

The light intensity has a great influence on the photosynthesis of organisms. It can be measured by an illuminance meter .


Illumination intensity refers to the energy of visible light received per unit area, referred to illuminance, , unit lux (Lux or lx). It is a physical term used to indicate the intensity of light and the amount of light that the surface area of ​​an object is illuminated.

In photometry , ” luminance ” is the density of luminous intensity in a specified direction , but it is often misunderstood as illuminance . The international unit of luminosity is the candle light per square meter (called candela in Mainland China, Hong Kong and Macau ).

Illumination /illuminance on a surface illuminated by light is defined as the luminous flux illuminating a unit area .

Suppose the luminous flux on the surface element dS is d Φ , then the illuminance E on this surface element is: E=d Φ /dS.

1 lx=1 lm/㎡. For an object that is uniformly illuminated by light, when the luminous flux obtained on an area of ​​1 square meter is 1 lumen , its illuminance is 1 lux . Lumen is a unit of luminous flux.

A point light source with a luminous intensity of 1 candela has a luminous flux of “1 lumen” per unit solid angle (1 steradian ) .

Candlelight (Candela), transliteration ” Candela “. The concept of candlelight was first invented by the British, and it is a unit of luminous intensity.

At that time, the British used a pound of white wax to make a one-foot-long candle to define the unit of candlelight. But today’s definition has changed: heating with a black luminous body of one cubic centimeter, until the luminous body melts into liquid, 1/60 of the amount of light emitted is the standard light source , and candlelight is the standard light source. The unit of light emitted.

The term

1. Natural lighting and artificial lighting

Sunlight is natural lighting, and light lighting is artificial lighting.

2. Light cycle and light time

In nature, 24 hours a day and night is a light cycle. The time with light is the bright period, and the time without light is the dark period. In natural light, the sunshine time is usually calculated as the sunshine time (bright period); in artificial light, the time of light exposure is the light time, and the 24h light cycle is the natural light cycle; the longer or shorter than 24h is called unnatural light Cycle; if there is only one bright period and one dark period in 24h, it is called single-period illumination; if there are two or more bright or dark periods in 24h, it is intermittent illumination. The sum of the bright periods in a photoperiod is the photoperiod.

3. Luminous intensity

The amount of luminous flux transmitted by a light source within a solid angle in a certain direction . Unit: Candela (candela, cd).

4. Luminous flux

The light energy radiated by the light source per unit time is called the luminous flux of the light source, and its unit is lumens (the amount of light on a 1 square foot area that is 1 foot away from the 1 candle light source is 1 lumen).

5. Related definitions

Illuminance is the degree to which an object is illuminated. That is, the ratio of the luminous flux obtained on the surface of the object to the illuminated area, the unit is lux Ix ( 1 lux is the illuminance produced by a luminous flux of 1 lumen evenly illuminated on an area of ​​1 square meter ) or foot candle fc ( 1 foot candle is 1 The luminous flux of lumens uniformly illuminates the illuminance produced on 1 square foot area ), 1 fc=10.76 lx.

Under direct sunlight in summer, the light intensity can reach 60,000 to 100,000 lx, outdoor with no sun 10,000 to 10,000 lx, bright indoor 100 to 550lx in summer, and 0.2lx under the full moon at night.

Incandescent lamps can emit approximately 12.56 lx of light per watt, but the value varies with the size of the bulb. Small bulbs can emit more lumens and large bulbs are less. Fluorescent lamp of the luminous efficiency three to four times the incandescent lamp, the incandescent lamp life is 9 times, but higher prices. In the light emitted by an incandescent bulb without a lampshade, about 30% of the lumens are absorbed by walls, ceilings, equipment, etc.; the poor quality and darkness of the bulb will reduce many lumens, so only about 50% of the lumens can be used. Generally, when there is a lampshade and the lamp height is 2.0~2.4m (the distance between the bulbs is 1.5 times the height), 1W bulbs are needed for every 0.37㎡ area, or 2.7W bulbs are needed for 1㎡ area, which can provide 10.76 lx. The height of the bulb installation and the presence or absence of the lamp cover have a great influence on the light intensity.

Calculation formula

Average illuminance (Eav) = total luminous flux of light source (N*Ф)*utilization factor (CU)*maintenance factor (MF) / area area (㎡)

(Applicable to indoor or stadium lighting calculation)

Utilization factor: 0.4 for general indoor, 0.3 for sports

Maintenance factor: generally 0.7~0.8

Example 1:

Indoor lighting: 4×5m room, using 9 sets of 3×36W grid lights,

Average illuminance=total luminous flux of light source×CU×MF/area=(2500×3×9)×0.4×0.8÷4÷5 =1080 Lux

Conclusion: The average illuminance is above 1000 Lux.

Example 2: Stadium lighting: 20×40m venue, using 60 sets of POWRSPOT 1000W metal halide lamps,

Average illuminance=total luminous flux of light source×CU×MF/area=(105000×60)×0.3×0.8÷20÷40 =1890 Lux

Conclusion: The average horizontal illumination is above 1500 Lux.

An office average illuminance design case:

Design conditions: The office is 18.2 meters long, 10.8 meters wide, the ceiling height is 2.8 meters, the desktop height is 0.85 meters, the utilization factor is 0.4, the maintenance factor is 0.8, and the number of lamps is 33 sets. What is the average illuminance in the office?

Lamp solution: The lamp adopts DiNiT 2X55W anti-glare daylight lamps, with a luminous flux of 3000Lm, a color temperature of 3000K, and a color rendering of Ra90 or more.

According to the formula: Eav = (33 sets X 6000Lm X 0.4 X 0.8) ÷ (18.2 meters X 10.8 meters)

= 110880.00 ÷196.56 ㎡

= 564.10Lux

Remarks: The lighting design must require accurate utilization factor, otherwise there will be a big deviation, which will affect the size of the utilization factor. There are mainly the following factors: the light distribution curve of the luminaire, the light output ratio of the luminaire, the indoor reflectivity , Such as ceiling, wall, work desk, etc., indoor index size.

Standard value


Maintain the average illuminance on the working surface or reference plane, and the average illuminance on the specified surface shall not be lower than this value. It is the average illuminance on the specified surface at the time when the lighting device must be maintained. This is the illuminance required to ensure visual safety and visual efficacy at work.


The standard values of illuminance are graded according to 0.5, 1, 2, 3, 5, 10, 15, 20, 30, 50, 75, 100, 150, 200, 300, 500, 750, 1000, 1500, 2000, 3000, 5000lx.

lx ( lux ) is the unit of illuminance .

The illuminance standard value classification is based on the subjective effect that the smallest change in illuminance is clearly felt. The illuminance difference is about 1.5 times. This classification is roughly consistent with the classification of the CIE International Luminous Lighting Committee standard “Indoor Workplace Lighting” S008/E-2001.

Lighting national standard data

The National Standard of the People’s Republic of China “Architectural Lighting Design Standard” GB 50034-2013 stipulates the general illuminance standard values ​​for newly built, rebuilt and expanded residential, public and industrial buildings.

Room (place)Reference plane and its heightStandard value of illuminance (lx)
Residential building living room (general activity)0.75m horizontal plane100
Residential building living room (writing and reading)0.75m horizontal plane300 suitable for mixed lighting
Residential building restaurant0.75m dining table150
Library General Reading Room0.75m horizontal plane300
Office building general office0.75m horizontal plane300
General supermarket business hall0.75m horizontal plane300
Hospital waiting room, registration hall0.75m horizontal plane200
School classroomClass desktop300
School classroom blackboardBlackboard surface500
Common corridors and mobile areas in public placesground50
Public places escalatorground50
Industrial construction machinery processing rough machining0.75m horizontal plane200
Industrial construction machinery processing general processing tolerance ≥ 0.1mm0.75m horizontal plane300 should add local lighting
Industrial construction machinery processing precision machining tolerance <0.1mm0.75m horizontal plane500 should add local lighting

When one or more of the following conditions are met, the illuminance of the working surface or reference plane can be increased by one level according to the standard value of degree.

  1. Fine workplaces with high vision requirements, when the distance from the eyes to the recognition object is greater than 500 mm;
  2. When continuous long-term intense visual work has adverse effects on the visual organs;
  3. Recognize moving objects, when the recognition time is short and it is difficult to recognize;
  4. When visual work has an important impact on operational safety;
  5. When the brightness contrast of the recognition object is less than 0.3;
  6. When the operation accuracy is high, and errors will cause great losses;
  7. When the visual ability is lower than normal;
  8. When the building level and function requirements are high.

When one or more of the following conditions are met, the illuminance of the working surface or reference plane can be reduced by one level according to the standard value of degree.

  1. When doing homework for a short time;
  2. When operation accuracy or speed is not important;
  3. When the building level and function requirements are low.

In general, the design illuminance value is compared with the standard illuminance value, and there may be a deviation of -10%—+10%.

Related equipment

Illuminance meter

The illuminance meter is a special equipment used to measure the level of light intensity. In some specific environments, there are strict requirements on the illuminance of light. For example, the inspection of drugs by manual has strict requirements on the illuminance of light.

Related principles

Germanium photocell as probes, current due to the different light intensity of light generated by the cell is different, then the DC current amplification, then after digital to analog conversion circuit of the DC signal into the light intensity of the reaction straightforward digital signal is displayed.


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