Understanding how the units of measurement "lumen" and "lux" are correctly related to each other, as well as where they are used, is necessary to successfully solve the following everyday situations:
- determination and verification of illumination in a residential area for compliance with the norm;
- the location of the fixtures in order to create the same illumination anywhere in the room;
- prevention of overexpenditure of electricity for lighting devices;
- prevention of eye diseases arising from lack of light, and negative bodily conditions caused by a violation of biorhythms.
Content
What is lumen and lux
Any light source can be characterized by the strength of the emitted light. In the international metric system, it is measured in candelas (cd). The derivative of the candela is a value that directly characterizes the luminous flux - lumen, abbreviated - lm.
Important: on modern lamps and products with LEDs, the value of the light flux emitted by them in lumens or the value of light output in lumens per watt (lm / W) is indicated.
Luminous efficiency in specific figures describes the efficiency of converting electrical energy into light and characterizes the efficiency of the lamp. To get only lumens, you need to multiply the value in lm / W by the value of the power of the product in watts. For example, the light output of a 100-watt incandescent lamp is 15 lm/W. So theoretically it emits light of 1500 lumens. In reality, there are always losses in aperture ratio. First of all, this is due to the material of the lamp itself.
Consideration of the movement of light waves in space inevitably leads to the concept of illumination, because light does not shine into itself, it is always directed outward from the source and makes other objects visible to the human eye. Obviously, in this case, it falls on the surface of a certain area, which makes it illuminated.
Lux is a unit of measure for illuminance. If a luminous flux of 1 lumen falls perpendicularly and uniformly on a surface area of a unit area (1 m²), its illumination will be 1 lux.
The absolute value of illumination in lux will always be a multiple of the value of the luminous flux in lumens for each specific light source, since the relationship between these values is inversely proportional. The larger the illuminated area, the worse the illumination characteristics. So, for example, an incandescent lamp of 1500 lm, placed in an opaque cube with a face area of 1 m², strictly in its center, that is, equidistant from all its sides, will illuminate only 6 m² (4 sides of 1 m², 1 bottom + 1 top). So the illumination inside such a cube will be:
1500 lm / 6 m² = 250 lx.
Now let the same light bulb in the chandelier illuminate a square - for ease of calculation - room with a wall length of 4 m. This will be the same cube with an area of \u200b\u200beach side of 16 m², and the total area will be 96 m². At the same time, for the purity of the calculation, the light bulb should be hung in the center of the room at a mark of 2 m from the floor and ceiling. Then the illumination at each point in the room would be:
1500 lm / 96 m² = 15.625 lx.
In practice, no one does this, the maximum length of the chandelier suspension is only 0.5 m. Focusing on visual sensations, a person will feel that there is more light directly under the light bulb than in the corners of the room, and a small area on the ceiling at the place where the lamp is attached is best illuminated provided that its design is open at the top.
In everyday life, in addition to luminosity, the following factors affect the illumination of the surface:
- distance to the light source;
- the location of the light source;
- its form;
- angle of incidence of light (rotation and inclination of the socles);
- the curvature of the surface itself;
- change in spatial characteristics;
- reflective surface properties (for example, a black velvet surface and mirrors should be illuminated differently).
Therefore, in practice, theoretical calculations are useless, and a luxmeter is used to measure illumination.
How to convert lux to lumens
However, if you know the desired value of illumination in lux and the area of the illuminated surface, you can calculate the required amount of luminous flux in lumens. At the same time, it should be understood that the calculation will be performed with many assumptions, since it is not possible to bring the conditions for its implementation closer to physically ideal ones. When calculating, it should be assumed that:
- the light source is located in the center;
- the illumination is uniform over the entire area, which is almost impossible;
- light falls at the same angle over the entire surface area;
- the surface is illuminated from within the thought sphere assumed to be around the source.
Important! The practical formulation of this task sounds much simpler: there is a norm of illumination in lux for a particular room, for example, for an office - 300 lux. How many lamps need to be placed to comply with it? To do this, the required value in lumens is first calculated. The inevitable unevenness in illumination can be corrected with additional backlighting.
In order to get the value in lumens, you need to multiply the norm in lux by the value of the area that needs lighting.
Example: Let an office with a norm of 300 lux have a wall length of 10 meters and a ceiling height of 4 meters. It is required to calculate the minimum number of lumens required to comply with the standard.
The floor and ceiling area will be: 10 x 10 = 100 m².
Area of each wall: 4 x 10 = 40 m².
Theoretically, with the assumption of uniform illumination and the location of the source, equidistant from all points on the surface, the problem is solved as follows:
300 lux x (4 x 40 + 100 + 100) m² = 300 x 360 = 108,000 lm.
If this astronomical value is "translated" into ordinary 100-watt incandescent lamps, then only ... 72 pieces are needed.
The practical approach will be different. There is absolutely no need to illuminate the ceiling - the workplaces of employees are below. Moreover, the design of many ceiling lights makes it impossible for the light to spread upwards. So from the calculations you need to remove the area of \u200b\u200bthe ceiling:
300 lx x 260 m² = 78,000 lm.
Modern ceiling lights with LEDs can produce 5,000 lumens.Accordingly, they will need 16 pieces (78,000/5000), rounded to the nearest whole number.
This number can be reduced. According to SanPiN 2.2.1 / 2.1.1.1278-03, the illumination is measured above the work surface, as well as at control points 1 m away from walls and light openings. It is enough to place lighting devices above the workplaces of employees. Mathematically reducing the geometric characteristics of the floor by 1 m on each side, we get:
300 lux x (160 + 64) m² = 300 x 224 = 67200 lm.
What in ceiling lights will be: 14 pieces rounded to the nearest whole number.
Lumen values for different lighting fixtures
Modern requirements for the packaging of lighting fixtures oblige to bring to the consumer their technical characteristics in full. Therefore, finding the value in lumens under the abbreviation "lm" or "lm" will be easy. For example:
- incandescent lamp 100 W - 1300-1500 lm;
- incandescent lamp 60 W "General Electric" - 660 lm;
- energy-saving lamp "NetHaus", halogen 13 W - 250 lm;
- LED lamp (LED) "Gauss Elementary" 12 W "as in 100 W" - 1130 lm;
- light-emitting diode (LED) lamp "Gauss Elementary" 6 W "as in 60 W" - 420 lm;
- LED lamp Elektrostandard LTB0201D 60 cm 18V - 1200 lm;
- LED table lamp Maytoni Nastro, 15 W - 900 lm;
- office lamp TL-ECO on LEDs 48.5 W - 4530 lm (final luminous flux after all losses).
As can be seen from the ratio of luminous flux to the power of the device, LED lighting devices are the most economical and efficient in terms of luminous efficiency.
Attention! Since all compact, tubular and industrial fluorescent lamps containing mercury and other hazardous metals have been banned in the Russian Federation since January 1, 2020, they were not included in the list.
Illumination standards
Sanitary rules SanPiN 2.2.1/2.1.1.1278-03 regulate the average illumination of buildings, structures and institutions for various purposes, as well as the illumination of stations, roads, pedestrian crossings, parks and stadiums.
Standards for artificial lighting in residential premises are as follows:
- office - 300 lx;
- children's room - 200 lux;
- living rooms and kitchen - 150 lux;
- dressing room - 75 lux;
- bathroom and bathroom - 50 lux;
- corridor - 50 lux;
- pantry - 30 lux.
However, in most cases, the illumination of rooms and residential areas is selected based on the personal preferences of the residents themselves, and compliance with the standard is carried out only in relation to production and work premises.
As a conclusion, it is worth remembering the following:
- The numerical value of the luminous flux is indicated on the packaging of the lighting product in lumens.
- To get the value of illumination in lux, it must be divided by the value of the area to be illuminated, expressed in square meters. meters.
- There are sanitary standards for the illumination of any type of room.
- Light-emitting diode (LED) lamps are the most economical and efficient in terms of light output.
