How to determine the required power of an LED lamp

When designing a lighting system, after repair or construction of an office or residential premises, it is necessary to make calculations so that there is enough light. It does not matter whether conventional incandescent lamps, compact fluorescent lamps or LED lamps are used, it is required to obtain such a luminous flux as a result so that it provides comfortable conditions for a person.

If we are talking about replacing incandescent lamps with LED ones, then in principle there is no problem in choosing LED lamps for the corresponding luminous flux, there are tables for this, since the average luminous flux for typical incandescent lamps for each specific rating is known, and the luminous flux of LED lamps can also be easily recognized simply by reading the inscription on the package.

But what to do if you want to get a modern lighting system based on LEDs, which can significantly save money when paying electricity bills?

How to choose LED lamps of the right power, in the right amount, and still not miss the light? How many lamps and how much power to install in a particular room? How to determine the required power of an LED lamp for a particular room?

This will be discussed further. We will figure out how to calculate the power correctly to get high-quality and comfortable lighting.

When it is necessary to provide illumination of a room or, say, an office of square or rectangular shape, the calculations are quite simple. If the shape of the room is a complex figure, then simply divide it into rectangles, at least approximately, and for each individual part, calculate the necessary illumination. So you get a pretty accurate picture of what power you have to rely on when buying LED lamps, and how many of these lamps will be needed.

Recall that Illumination is measured in lux (Lx)and the luminous flux of the lamp is in lumens (Lm). Therefore, first, the total luminous flux is calculated based on SNiP, where you can find out the standard illumination in suites for various rooms, and on room parameters, such as the area and height of the ceilings, and then the light flux is distributed between the LED lamps, and the power of each of them is determined.

Simplified formula for calculating luminous flux:

Φ = E * S * K,

where f is the total luminous flux in lumens; E - standard illumination in suites; S is the area of ​​the premises in square meters; K is the coefficient associated with the height of the ceilings.

The coefficient K is the greater, the higher the ceilings (the higher the lamp is located above the illuminated surface), since the light flux scatters with increasing area under the lamp, and the higher the ceiling, the wider the light cone, the larger the diameter of the light spot and its area. So, depending on the height of the ceilings, the coefficient K takes the following values:

• K = 1 with a ceiling height of 2.5 to 2.7 meters;

• K = 1.2 with a ceiling height of 2.7 to 3 meters;

• K = 1.5 with a ceiling height of 3 to 3.5 meters;

• K = 2 with a ceiling height of 3.5 to 4.5 meters.

The standard illumination E is taken from SNiP 23-05-95 (initially) "Natural and artificial lighting." Here are some lighting values ​​in suites for residential and office buildings:

• E = 500 Lx - for offices where drawing work is carried out;

• E = 300 Lx - for general-purpose offices using computers;

• E = 300 Lx - for classrooms and libraries;

• E = 200 Lx - for conference rooms, meeting rooms, children's rooms;

• E = 150 Lx - for living rooms and kitchens;

• E = 100 Lx - for saunas, pools, stairs, escalators;

• E = 75 Lx - for dressing rooms, archives, office corridors and halls;

• E = 50 Lx - for bathrooms, bathtubs, apartment halls and corridors;

• E = 20 Lx - for lighting stairs.

Area S is taken in square meters, in relation to the room that will be lit with LED lamps, based on your needs.

As a result, by calculating the value of Ф, it is possible to easily select the LED lamps in the right amount, simply dividing the Ф by the luminous flux of each selected lamp, and determine its power by the luminous flux of each LED lamp. A table is provided for this. How many lamps will provide the total luminous flux, each one decides for himself, based on individual conditions.

Let's consider the following problem as an example. The living room has dimensions of 3 by 5 meters, that is, its shape is a rectangle, and the area S = 3 * 5 = 15 square meters. The ceiling height is 2.4 meters, respectively, we take K = 1. We take illumination equal to 150 Lux, in accordance with the regulations on SNiP.

So, we have for our example: E = 150; S = 15; K = 1. Total: Ф = Е * S * К ​​= 150 * 15 * 1 = 2250 Lm.

Knowing the total luminous flux in lumens, it is not difficult to choose LED lamps. For example, we decided to use 6 lamps, then the luminous flux of each of them should be equal to 2250/6 = 375 Lm. We choose 5 watt LED bulbs in the amount of 6 pieces, which we will evenly place over the ceiling area.

Meanwhile, it is important to remember that the more light sources are placed in the room, the more even and comfortable the light will be. If the lighting should be uniform, then the bulbs are placed at the same distance from each other. If you want to get a more dense light in a particular area, then the bulbs are combined so that this area is emphasized.

In fairness, we note that the standards regulated by SNiP do not always give the result that everyone would like. For example, someone will have little light calculated according to SNiP, someone likes a brighter light, someone more dim. For this reason, you should focus on your preferences. If you like it to be very light, feel free to multiply the standard value of E by 2.

To achieve finer tuning for different times of the day, use zoning lighting, or use dimmable LED lamps in conjunction with special dimmer.