Light is that without which nothing could exist on Earth. Like all physical quantities, it can be calculated, which means that there is a unit of measurement of luminous flux. What is it called and what is it equal to? Let's find the answers to these questions.
What is called a "light stream"
First of all, it is worth understanding what is called this term in physics.
Luminous flux - the power of light emission, estimated by the light sensation it produces from the point of view of the human eye. This is a quantitative characteristic of the radiation of a light source.
The numerically considered quantity is equal to the energy of the light flux passing through a certain surface per unit time.
Unit of measurement of luminous flux
What is the physical quantity under consideration measured in?
According to the current norms of SI (International System of Units), a specialized unit called lumen is used for this.
This word was formed from a Latin noun meaning "light" - lΕ«men. By the way, the name also came from the name of the secret organization, the Illuminati, which became a subject of general interest several years ago.
In 1960, lumen officially began to be used around the world as a unit of measurement of luminous flux, and remains so until today.
In abbreviated form in Russian, this unit is written as βlmβ, and in English - lm.
It is worth noting that in many countries the power of light bulbs is not measured in watts (as in the open spaces of the former USSR), but in lumens. In other words, overseas consumers do not consider the amount of energy consumed, but the power of the emitted light.
By the way, because of this, on the packages of most modern energy-saving light bulbs there is information about their characteristics both in watts and in lumens.
Formula
The considered unit of measurement of luminous flux is numerically equal to light from a point isotropic source (with a force in candela) radiated into a solid angle equal to one steradian.
In the form of a formula, it looks like this: 1 lm = 1cd x 1 cf.
If we take into account that the full sphere forms a solid angle of 4P sr, it turns out that the total luminous flux of the above source with a power of one candela is 4P lm.
What is a candela?
Having learned that lumen is what, it is worth paying attention to the unit associated with it. It's about cd - that is, candela.
This name was derived from the Latin word "candle" (candela). From 1979 to this day, it has been a unit of measurement of luminous intensity, according to SI (International System of Units).
In fact, one candela is the power of light emitted by one candle (hence the name). It is worth noting that in the Russian language for a long time instead of the term "candela" the word "candle" was used. However, this name is outdated.
From the previous paragraph it is clear that lumen and candela are interconnected (1 lm = 1 cd x 1 sr).
Lumens and Suites
Considering the features of such a luminous quantity as a lumen, it is worth paying attention to such a concept close to it as "lux" (lux).
Like candelas with lumens, suites also belong to lighting units. Lx is a unit of measurement of illumination used in the SI system.
The relationship between lux and lumen is as follows: 1 lux is equal to 1 lm of the light flux evenly distributed on the surface of 1 square meter. Thus, in addition to the above lumen formula (1 lm = 1cd x 1 sr), this unit has one more: 1 lm = 1 lx / m 2 .
In simpler terms, a lumen is an indicator of the amount of light emitted by a particular source, for example, the same light bulb. But the suite shows how real light is in the room, since not all light rays reach the illuminated surface. In other words, lumen is light coming out of a source, lux is the amount of it that really reached the illuminated surface.
As already mentioned, not all the emitted light always reaches the illuminated surface, because often in the way of such rays there are obstacles that create shadows. And the more they are on the way, the less light.
For example, during the construction of the library hall, a lot of light bulbs were hung in it. The total illumination of this empty room was 250 lux. But when the repair work was completed and furniture was brought into the room, the light level dropped to 200 lux. This despite the fact that the bulbs, as before, gave out as many lumens of light energy. However, obstacles in the form of shelving with books and other library furniture, as well as visitors and workers, now appeared on the path of each of its rays. Thus, they absorbed part of the emitted light, reducing the total amount of illumination to the hall.
The situation given as an example is not an exception of its kind. Therefore, when building any new buildings or decorating existing ones, it is always important to consider its illumination. For most institutions, there is even a system of lighting standards, of course, it is measured in suites.
In the modern world there are several programs in which you can not only simulate your own room design, but also calculate how bright it will be. Indeed, the vision of its inhabitants depends on this.
Lumen and watt
In the past, in our country, when choosing a bulb, they were guided by the number of watts that it consumes. The more of the more, the better this device shone.
Today, even in domestic spaces, its radiation power is increasingly measured in lumens. In this regard, some believe that lm and W are values ββof the same kind, which means that lumens into watts and vice versa can be freely converted, like some other units of the SI system.
This opinion is not entirely true. The fact is that both units under consideration are used for different quantities. So, a watt is not a light, but an energy unit showing the power of a light source. While the lumen shows how much light is emitted by a particular device.
For example, an ordinary incandescent lamp, consuming 100 watts, produces 1340 lumens of light. At the same time, its more advanced (today) LED "sister" when consuming only 13 watts produces 1000 lm. Thus, it turns out that the aperture ratio of a bulb is not always directly dependent on the amount and power of energy absorbed by it. An important role in this matter is played by the substance used for lighting in the device. So, there is no direct relationship between lumens and watts.
Moreover, these quantities are indeed interconnected. Luminous efficiency of any light source (the interdependence of energy consumed to the amount of light emitted) is measured in lumens per watt (lm / W). This unit is a testament to the effectiveness of a particular lighting device, as well as its efficiency.
It is worth noting that with great need, you can still convert lumens to watts and vice versa. But for this you need to consider several additional nuances.
- The nature of the light source. Which lamp is used in the calculations: incandescent, LED, mercury, halogen, fluorescent, etc.
- The luminous efficiency of the device (how many watts it consumes and how many lumens it emits at the same time).
However, in order not to complicate your life, to carry out such calculations, you can simply use the online calculator or download a similar program to your computer or other device.
Multiple Lumens
Lumen, like all its "relatives" in the SI system, has a number of standard multiple and fractional units. Some are used for simplicity of calculations, when you have to deal with either too small or too large quantities.
If we are talking about the latter, then they are written in the form of a positive degree, if about the former - in the form of a negative. So, the largest multiple unit of lumen - iottalumen - is equal to 10 24 lm. It is most often used in characterizing cosmic bodies. For example, the luminous flux of the Sun is 36300 Ilm.
Most often, four multiple units are used: kilolumen (10 3 ), megalumen (10 6 ), gigalumen (10 9 ) and teralumen (10 12 ).
Fractional units of lumen
The smallest fractional unit of lumen is ioctolumen - ilm (10 -24 ), however, like ottumumen, it is practically not used in real calculations.
The most commonly used units are millillumen (10 -3 ), microlumen (10 -6 ) and nanolumen (10 -9 ).