Calculation formulas for luminous flux and illuminance|flood light supplier|Sunshinelux

July 10, 2022

Illuminance calculation formula: average illuminance (Eav) = total luminous flux of light source (N*Ф) * utilization factor (CU) * maintenance factor (MF) / area area (㎡)


(for indoor or stadium lighting calculations)

Utilization coefficient: 0.4 for general indoor use and 0.3 for sports

Maintenance factor: generally take 0.7 to 0.8

Example: Indoor lighting: 4 x 5 meters room, use 9 sets of 3 x 36W grille 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 more than 1000Lux.

Light intensity refers to the energy of visible light received per unit area, referred to as illuminance, in lux (Lux or Lx). A physical term used to indicate the intensity of light and the amount of light on the surface area of an object.


The luminous flux is equivalent to the water flow, the water flow is how much water flows out, flows or flows in one second, and the luminous flux is how much light flows out, flows or flows in one second, and the unit is lumens (Lm).

The illuminance is equivalent to how many lumens of light flow into a square meter area. Whether the water flow is urgent or not, not only the water flow rate, but also the water flow rate per unit area. That is to say, the cross-sectional area of the big river is 10 square meters, and the water flow is 10 cubic meters per second; the cross-sectional area of the small river is 1 square meter, and the water flow is 3 cubic meters per second; then the water flow of the small river is rapid. Illuminance means this, whether it is bright or not depends on the illuminance, and its unit is lux (Lx).


Illuminance, commonly referred to as lux, represents the luminous flux per unit area of the subject's surface. 1 lux is equivalent to 1 lumen/square meter, that is, the luminous flux irradiated vertically by a light source with a distance of one meter and a luminous intensity of 1 candle per square meter of the subject. Illuminance is an important indicator to measure the shooting environment.


Indoor lighting utilization coefficient method to calculate the average illuminance:

When we usually do illuminance calculation, if we know the utilization coefficient "CU", we can easily use an empirical formula to quickly calculate to find the average illuminance value of the indoor working surface we want. We usually refer to this calculation method as "using the coefficient method to find the average illuminance", also known as the lumen coefficient method.

There are two types of illuminance calculation: rough calculation and precise calculation.


For example, suppose that the overall illuminance should be 100 lux (lx) like a house, and even 90 lux (lx) will not have a big impact on life. However, if it is road lighting, the situation is different. Assuming that the road illuminance must be 20 lux (lx), if it is 18 lux (lx), it may cause frequent traffic accidents.

The same is true for stores. For example, the overall optimal illuminance of the store is 500 lux (lx). Since the illuminance of 600 lux (lx) is used, the number and power of lighting fixtures will increase, and it will have an economic impact.


Whichever illuminance calculation is used is important. Although it is only a rough estimate, there will be a 20%-30% error. Therefore, it is recommended that in general, it is best to use professional lighting design software for accurate simulation calculation to control the error within the minimum range.

But sometimes we cannot use lighting software to simulate calculation due to special circumstances or limited site conditions, the following basic formula can be used to calculate the average illuminance of the floor, desktop and work surface, and the illuminance of the lamp (lux lx) = luminous flux ( Lumen lm)/area (square meter m^2) is the average illuminance of 1 lux (lx), which is the brightness of a luminous flux of 1 lumen (lm) illuminated on an area of 1 square meter (m^2). When using this method to find the average illuminance of the room floor, in the case of integral lighting, the following formula can be used to calculate.

Average illuminance (Eav) = luminous flux of a single lamp × number of lamps (N) × space utilization coefficient (CU) × maintenance coefficient (K) ÷ floor area (length × width) Formula Description

1. The luminous flux Φ of a single lamp refers to the total luminous flux value of the bare light source of the light source contained in the lamp.

2. The space utilization coefficient (CU) refers to the percentage of the light beam emitted from the lighting fixtures that reaches the floor and work surface, so it is related to the design, installation height, room size and reflectivity of the lighting fixtures. The rate also changes accordingly. For example, when the common lamp panel is used in a space of about 3 meters high, its utilization factor CU can be between 0.6-0.75; and when the aluminum cover of the lamp is suspended and the space height is 6-10 meters, its utilization factor CU can be in the range of 0.7- -0.45; when the downlight lamps are used in a space of about 3 meters, the utilization factor CU can take 0.4--0.55; and when the lamps such as light strip brackets are used in a space of about 4 meters, the utilization coefficient CU can take 0.3--0.5 . The above data are empirical values and can only be used for rough estimation. If you want to accurately calculate the specific values, you need to provide the company in writing. The relevant parameters are here for reference only.

3. It means that with the aging of the lighting fixture, the light output capacity of the lighting fixture decreases and the use time of the light source increases, and the light source decays; or due to the accumulation of dust in the room, the space reflection efficiency is reduced, resulting in a decrease in illuminance. Coefficient. Generally clean places, such as living rooms, bedrooms, offices, classrooms, reading rooms, hospitals, high-end brand stores, art galleries, museums, etc., the maintenance coefficient K is 0.8; while general stores, supermarkets, business halls, theaters The maintenance coefficient K of places such as machining workshops and stations is 0.7; and the maintenance coefficient K of places with a larger pollution index can be taken to be about 0.6. Using the coefficient method

This method is used to calculate the average illuminance

(Light source luminous flux) (CU) (MF) / irradiated area area

Suitable for indoor, sports lighting

Utilization coefficient (CU): generally indoors take 0.4, sports take 0.3

1. Illumination distribution of lamps

2. Lamp efficiency

3. The relative position of the lamps in the irradiation area

4. Reflected light in the enclosed area Maintenance factor MF=(LLD)X(LDD) generally takes 0.7~0.8

Example 1: Indoor lighting, 4 x 5 meters room, use 9 sets of 3 x 36W grille lights

Calculation formula: average illuminance = total luminous flux of light source × CU × MF / area



Conclusion: The average illuminance is above 1000Lux

Example 2: Gymnasium lighting, 20×40 meters field,

Use POWRSPOT 1000W metal halide lamp 60 sets

Average illuminance = total luminous flux of light source × CU × MF / area



Conclusion: The average level of illumination is above 1500Lux

Vertical illuminance above 1000Lux (depending on installation location)


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