Calculation of room illumination by hand to hand
I will try to very briefly and simply explain the method of manual calculation of lighting in rooms, which I was taught on the course “Calculation of lighting” of the LiDS lighting design school.
What should be the light
When planning the lighting, first of all you need to determine the target illumination corresponding to the norms and calculate the total luminous flux that the lamps should give in the room.
It is easy to determine the standards - either we are looking for our type of room in the tables SanPiN 2.21 / 2.1.1 / 1278-03 “Hygienic requirements for natural, artificial and combined lighting of residential and public buildings” and SP 52.13330.2011 “Natural and artificial lighting” , or We agree with the basic requirement for the illumination of residential premises - 150lk or office premises with computers - 400lk.
Rough estimate of the required luminous flux
By default, the calculation of light is done in the program Dialux . But the result is at least approximately necessary to know in advance in order to verify the data with the estimate "by eye".
As written even in Wikipedia, the average illumination of the surface is the ratio of the luminous flux falling on it to the area. But in a real room, a part of the luminous flux of the lamp does not reach the working planes, disappearing on the walls. Room illumination is the ratio of the total luminous flux of luminaires to the area of a room with a correction factor “η”.
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The proportion of light "η", which reaches the working surfaces, can be estimated by eye. In the most general approximation, for some very average room with some kind of luminaire, about half of the light reaches the working surfaces, which means that for a very rough estimate, you can use the coefficient η = 0.5.
For example, in a room with an area of 20m 2, a luminaire with a luminous flux of 700lm ( equivalent to an incandescent lamp of 60W ) will create illumination E = 0.5 × 700lm / 20m 2 = 18lx. And this means that to achieve a standard of 150 lk, you need F = 700 lm × (150 lk / 18 lk) = 5800 lm, or the equivalent of 8 incandescent bulbs of 60W each!
(A half-kilowatt incandescent lamp for a small room! It is clear why the illumination standards for residential premises are much lower than for institutions, and why no one has been illuminating incandescent lamps for a long time.)
More accurate manual calculation method
But since the premises come with different walls, different shapes, with high or low ceilings, the correction factor is not necessarily 0.5 and for each case it is different: in practice, from 0.1 to 0.9. Despite the fact that the difference between η = 0.3 and η = 0.6 already means a run-up of the results in two times.
The exact value of η must be taken from the tables of the utilization of the luminous flux developed in the USSR. In full view with explanations of the table cite in a separate document . Here we will use an excerpt from the tables for the most popular case. For a standard bright room with the reflection coefficient of the ceiling of the walls and floor in 70%, 50%, 30%. And for ceiling-mounted luminaires that shine by themselves and a little sideways (that is, they have a standard, so-called "cosine" light intensity curve).
Tab. 1 The coefficients of the use of the luminous flux for ceiling lamps with a cosine diagram in the room with the reflectances of the ceiling, walls and floor are 70%, 50% and 30%, respectively.
In the left column of the table is the index of the room, which is calculated by the formula:
where S is the area of the room in m 2 , A and B is the length and width of the room, h is the distance between the luminaire and the horizontal surface on which the illumination is calculated.
If we are interested in the average illumination of working surfaces (table) in a room with an area of 20m 2 with walls 4m and 5m, and the height of the suspension of the lamp above the tables 2m, the index of the room will be i = 20m 2 / ((4m + 5m) × 2.0m) = 1.1. Making sure that the room and the lamps correspond to those indicated in the caption for the table, we obtain the utilization factor of the luminous flux - 46%. The factor η = 0.46 is very close to the assumed offhand η = 0.5. The average illumination of working surfaces with a total luminous flux of 700 lm will be 16 lk, and to achieve the target 150 lk, you will need F = 700 lm × (150 lk / 16 lk) = 6500 lm.
But if the ceilings in the room were half a meter higher, and the room was not “light”, but “standard” room with the reflectance of the ceiling, walls and floor 50%, 30% and 10%, the utilization factor of the light flux η would be (see . Extended version of the table ) η = 0.23, and the illumination would be exactly half as much!
Checking calculations in dialux
Let's build a room in the roomyx 4 × 5m, height 2.8m, with the height of the working surfaces 0.8m and the same reflection coefficients as with manual counting. And we will hang up 9 pieces of small lamps with a classical cosine diagram of 720 l each (6480 l per circle).
Fig. 1 Taken as an example, the Philips BWG201 luminaire with a luminous flux of 720 lm, and its classic "cosine" light distribution
Will we have an average illumination of working surfaces in 150lk, as we estimated manually? Yes, the result of the calculation in Dialux is 143lk (see fig. 2), and in an empty room without furniture and a human figure - 149lk. In light engineering, values that differ by less than 10% are considered to be coincident.
Fig. 2 The result of the calculation in dialux is the average illumination of the working surface (with a safety factor of 1.0) was 143 lx, which corresponds to the target value of 150 lx.
Fig. 3 Beautiful pictures that people believe in.
Conclusion:
A rough estimate by the primitive method using the formula E = 0.5 × F / S will take 1 minute, another 3 minutes to refine the utilization rate according to the tables, about 20 minutes to the project in the dialux after some training, and another 20 minutes if you want to “bring beauty. Dialux gives out very beautiful pictures (see fig. 3), which are worth the labor, because people believe in them. But in terms of the ratio of efficiency and labor, the evaluation of illumination by hand to hand is out of competition. Manual counting is simple, reliable and effective as a sapper blade, gives confidence and understanding.
What should be the light
When planning the lighting, first of all you need to determine the target illumination corresponding to the norms and calculate the total luminous flux that the lamps should give in the room.
It is easy to determine the standards - either we are looking for our type of room in the tables SanPiN 2.21 / 2.1.1 / 1278-03 “Hygienic requirements for natural, artificial and combined lighting of residential and public buildings” and SP 52.13330.2011 “Natural and artificial lighting” , or We agree with the basic requirement for the illumination of residential premises - 150lk or office premises with computers - 400lk.
Rough estimate of the required luminous flux
By default, the calculation of light is done in the program Dialux . But the result is at least approximately necessary to know in advance in order to verify the data with the estimate "by eye".
As written even in Wikipedia, the average illumination of the surface is the ratio of the luminous flux falling on it to the area. But in a real room, a part of the luminous flux of the lamp does not reach the working planes, disappearing on the walls. Room illumination is the ratio of the total luminous flux of luminaires to the area of a room with a correction factor “η”.
')
The proportion of light "η", which reaches the working surfaces, can be estimated by eye. In the most general approximation, for some very average room with some kind of luminaire, about half of the light reaches the working surfaces, which means that for a very rough estimate, you can use the coefficient η = 0.5.
For example, in a room with an area of 20m 2, a luminaire with a luminous flux of 700lm ( equivalent to an incandescent lamp of 60W ) will create illumination E = 0.5 × 700lm / 20m 2 = 18lx. And this means that to achieve a standard of 150 lk, you need F = 700 lm × (150 lk / 18 lk) = 5800 lm, or the equivalent of 8 incandescent bulbs of 60W each!
(A half-kilowatt incandescent lamp for a small room! It is clear why the illumination standards for residential premises are much lower than for institutions, and why no one has been illuminating incandescent lamps for a long time.)
More accurate manual calculation method
But since the premises come with different walls, different shapes, with high or low ceilings, the correction factor is not necessarily 0.5 and for each case it is different: in practice, from 0.1 to 0.9. Despite the fact that the difference between η = 0.3 and η = 0.6 already means a run-up of the results in two times.
The exact value of η must be taken from the tables of the utilization of the luminous flux developed in the USSR. In full view with explanations of the table cite in a separate document . Here we will use an excerpt from the tables for the most popular case. For a standard bright room with the reflection coefficient of the ceiling of the walls and floor in 70%, 50%, 30%. And for ceiling-mounted luminaires that shine by themselves and a little sideways (that is, they have a standard, so-called "cosine" light intensity curve).
Tab. 1 The coefficients of the use of the luminous flux for ceiling lamps with a cosine diagram in the room with the reflectances of the ceiling, walls and floor are 70%, 50% and 30%, respectively.
In the left column of the table is the index of the room, which is calculated by the formula:
where S is the area of the room in m 2 , A and B is the length and width of the room, h is the distance between the luminaire and the horizontal surface on which the illumination is calculated.
If we are interested in the average illumination of working surfaces (table) in a room with an area of 20m 2 with walls 4m and 5m, and the height of the suspension of the lamp above the tables 2m, the index of the room will be i = 20m 2 / ((4m + 5m) × 2.0m) = 1.1. Making sure that the room and the lamps correspond to those indicated in the caption for the table, we obtain the utilization factor of the luminous flux - 46%. The factor η = 0.46 is very close to the assumed offhand η = 0.5. The average illumination of working surfaces with a total luminous flux of 700 lm will be 16 lk, and to achieve the target 150 lk, you will need F = 700 lm × (150 lk / 16 lk) = 6500 lm.
But if the ceilings in the room were half a meter higher, and the room was not “light”, but “standard” room with the reflectance of the ceiling, walls and floor 50%, 30% and 10%, the utilization factor of the light flux η would be (see . Extended version of the table ) η = 0.23, and the illumination would be exactly half as much!
Checking calculations in dialux
Let's build a room in the roomyx 4 × 5m, height 2.8m, with the height of the working surfaces 0.8m and the same reflection coefficients as with manual counting. And we will hang up 9 pieces of small lamps with a classical cosine diagram of 720 l each (6480 l per circle).
Fig. 1 Taken as an example, the Philips BWG201 luminaire with a luminous flux of 720 lm, and its classic "cosine" light distribution
Will we have an average illumination of working surfaces in 150lk, as we estimated manually? Yes, the result of the calculation in Dialux is 143lk (see fig. 2), and in an empty room without furniture and a human figure - 149lk. In light engineering, values that differ by less than 10% are considered to be coincident.
Fig. 2 The result of the calculation in dialux is the average illumination of the working surface (with a safety factor of 1.0) was 143 lx, which corresponds to the target value of 150 lx.
Fig. 3 Beautiful pictures that people believe in.
Conclusion:
A rough estimate by the primitive method using the formula E = 0.5 × F / S will take 1 minute, another 3 minutes to refine the utilization rate according to the tables, about 20 minutes to the project in the dialux after some training, and another 20 minutes if you want to “bring beauty. Dialux gives out very beautiful pictures (see fig. 3), which are worth the labor, because people believe in them. But in terms of the ratio of efficiency and labor, the evaluation of illumination by hand to hand is out of competition. Manual counting is simple, reliable and effective as a sapper blade, gives confidence and understanding.
Source: https://habr.com/ru/post/375931/
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