Detailed description of the luminous flux of LED bulbs
When designing room lighting systems, certain values need to be guided in order to unify calculation procedures. These same universal values are required for general consumers to navigate through the different types of light sources. For a long time, for incandescent bulbs, that value was one watt of electrical power consumption. But these devices are leaving the scene, so something else is needed.
What is the luminous flux
In fact, to calculate the illuminance designers previously used another value - candela (candle), which also has a direct correspondence to the watts consumed by the incandescent lamp. In the technical literature of the beginning of the second half of the last century you can find the expression "thousand-candle lamp", etc. Candela brightness refers to the power of light in watts emitted in a certain direction. As a visual association, this brightness is provided by an ordinary burning paraffin or stearin candle. Hence the name. This approach provides a visual representation of brightness as the number of candles burning.
Important! The watts used to calculate candela have nothing to do with electrical power - the light source may not be electric (the same candle).
For the concept of light flux, there is a definition - the power of radiation energy, which is evaluated by the light sensation. Or the number of photons emitted per unit time. Mathematically it looks like this: if a point source with power of 1 candela radiates flux to a solid angle equal to one steradian, it creates luminous flux of 1 lumen (lm).
The concept of the steradian needs clarification. In order to represent a solid angle of 1 cfu, we have to take a cone with the vertex in the center of a sphere of radius R, which cuts an area equal to R2 . The opening angle of such a cone is about 65 degrees.
If a point light source of 1 candela, radiating equally in all directions, is placed in a sphere with a radius of 1 m, on its inner surface will be created illumination equal to 1 lux (lx). This value is used to set norms of illumination. So, for different rooms, according to SNIP, the conditions must be met:
- classrooms of secondary schools - 500 lux;
- classrooms of higher educational institutions - 400 lux;
- gymnasiums - 200 lux.
Norms of illumination are also set for other rooms.
If the light flux of 1 lm falls on 1 sq.m. surface, it creates illumination of 1 lux. Hence the relation between lumen and lux: 1 lux = 1 lm/sq.m. For example, to provide sufficient illumination in an auditorium of 100 sq.m., a luminous flux of 40000 lumens is required. Also it should be taken into account that luminance decreases in proportion to the square of the distance from the light source, so the height of the luminaire suspension makes a difference.
Principle of operation
To understand the usability of all these quantities, it is necessary to consider the direction of emission of the LED, and related concepts.
The design of a light-emitting diode is such that it does not send light evenly in all directions - the lower hemisphere is covered by a substrate, and the lens design is such that it does not provide uniform radiation in the upper hemisphere. As a result, the main light flux is concentrated in the upper direction and weakens to the periphery of the light cone. At a certain angle of view the luminous intensity is reduced by half, and at an even greater angle the light becomes invisible. The first angle (bac) is called the angle of half luminance, and the second angle (fah) is called the full angle of luminescence.
The same points apply to the phosphor LED. There, the emission angle is limited by the substrate and the angle of the greatest activity of the initiating radiation of the p-n junction. It should be understood that it is impossible to accurately determine these angles by eye - you need special devices. But you can visually compare the two LEDs - which one has a larger opening angle.
Light output of LED lamps
The light output of LED lamps does not depend on the degree of heating of the crystal. Virtually all white LED lights are made on the basis of LED phosphor, so the light output depends on the quality of the phosphor, the technology by which it is produced. Also of importance is the light emission of the initiating crystal and the ability of this radiation to cause the phosphor to glow in the visible part of the spectrum.
The strength of the luminous flux of outdoor lighting
To calculate the outdoor lighting should be based on minimum lighting standards, which can also be found in the relevant SNiP (SP). For example, for playgrounds, the minimum illumination should not be less than 10 lux.
In the standards are given the minimum values of illumination, in the calculations they can be increased.
In order to get the required number of luminaires (N) to obtain the required illuminance, you should specify the initial data:
- minimum illumination (E), lux;
- area of the territory (S), sq.m;
- Lighting irregularity factor (z), for LED lights it is equal to 1.2;
- multiplier, taking into account the weakening of the luminous flux at the end of life of the luminaire (k), for LED fixtures it is equal to 1.2;
- luminous flux of one lamp (F), lm;
- is a factor that takes into account the reflection of objects located nearby (n), for asphalt it can be taken at 0.3.
These values are related by the formula N=E*S*z*k/(F*n).
Let us need to illuminate the playground area of 150 sq.m. There are fixtures that emit a luminous flux of 1500 lm each. Having substituted values in formula we get N=10*150*1,2*1,2/(1500*0,3). You get 4.8 or 5 luminaires. This is the minimum number, in fact, you can install more.
You can ask not the luminous flux of the existing lights, but the number of lights that can be installed in the area. In this case, you need to calculate the luminous flux of each lamp. The formula will look like F=E*S*k*z/(N*n). If the final result does not fall into the standard series of the characteristics of the lampsyou have to round it up.
Relationship of lumens and watts
Consumers around the world for decades of dominance of incandescent lamps used to correlate the brightness of lighting with the electric power consumption. For these outdated devices it was reasonable - the development of technology in this direction has long been at a standstill. The ratio of power to light intensity settled and got into the habit.
For LED lighting there is no direct correlation between power consumption in watts and light output in lumens. More precisely, it exists, but only at the moment. Technology does not stand still, crystal production is improving, new phosphors with higher light output are being developed. Ratios of the present time tomorrow will be hopelessly outdated.
Table of luminance
At the moment the correspondence of the luminous flux of modern LED lamps and their power consumption is as follows:
| Luminous flux, lm | 250 | 400 | 650 | 1300 | 2100 |
| Power consumption of LED lamp, W | 2-3 | 5-7 | 8-9 | 14-15 | 22-27 |
| Equivalent power of incandescent lamp, W | 25 | 40 | 60 | 100 | 150 |
In the table above are approximate rounded values, since the lamps that are on the market produced in a few years different manufacturers with different technologies. To the perception "by eye" this variation is practically invisible.
To conclude the video: Distinction and correlation of watts, lumens and Kelvin.
With a clear understanding of the relationship of the characteristics of light radiation, you can independently perform a calculation of the lighting of a room or territory. To do this, you need to know the standards of illumination and technical characteristics of LED-lamps.