Today we will tell you all about the illumination formula for open areas and indoors, as well as give the magnitude of the luminous flux under different circumstances.
Candle and spinning wheel
Before widespread electrification, the source of light was the sun, the moon, the fire and the candle. Scientists already in the fifteenth century knew how to create a system of lenses to enhance illumination, but most people worked and lived by candlelight.
Some felt sorry for spending money on wax lights, or this way to prolong the day was simply not available. Then they used alternative fuel options - oil, animal fat, wood. For example, Russian peasant women of the middle zone wove flax all their lives by the light of a splinter. The reader may ask: "Why did this have to be done at night?" After all, the coefficient of natural light during the day is much higher. The fact is that during the daytime, peasant women had many other worries. In addition, the weaving process is very painstaking and requires peace of mind. It was important for women that no one stepped on the canvas, so that the children would not confuse the threads, and the men would not distract.
But with such a life there is one danger: the luminous flux (we formulagive a little lower) from the torch is very low. Eyes strained and women quickly lost their sight.
Lighting and learning
When first graders go to school on the first of September, they expect miracles with excitement. They are captured by the ruler, flowers, beautiful shape. They are interested in what their teacher will be like, with whom they will sit at the same desk. And a person remembers these feelings for the rest of his life.
But adults, when sending their children to school, should think about more prosaic things than delight or disappointment. Parents and teachers are concerned about the comfort of the desk, the size of the classroom, the quality of the chalk, and the lighting formula in the room. These indicators have norms for children of all ages. Therefore, schoolchildren should be grateful that people thought out in advance not only the curriculum, but also the material side of the issue.
Lighting and work
It is not for nothing that schools conduct inspections in which a formula for calculating the illumination of rooms for classes is applied. Children of ten or eleven do nothing but read and write. Then they do their homework in the evening, again not parting with pens, notebooks and textbooks. After that, modern teenagers are also stuck in a variety of screens. As a result, the whole life of a schoolchild is associated with a load on vision. But school is only the beginning of life. Further, all these people are waiting for a university and work.
Each type of work requires its own light output. The calculation formula always takes into account thata person does 8 hours a day. For example, a watchmaker or jeweler must consider the smallest details and shades of colors. Therefore, the workplace of people in this profession requires large and bright lamps. A botanist who studies the plants of the rainforest, on the contrary, needs to constantly stay in the twilight. Orchids and bromeliads are used to the fact that the upper tier of trees takes almost all the sunlight.
Formula
Coming directly to the illumination formula. Her mathematical expression looks like this:
Eυ=dΦυ / dσ.
Let's take a closer look at the expression. Obviously, Eυ is the illumination, then Φυ is the luminous flux, and σ is a small unit of area on which the flux falls. It can be seen that E is an integral value. This means that very small segments and pieces are considered. That is, scientists sum up the illumination of all these small areas to get the final result. The unit of illumination is lux. The physical meaning of one lux is such a luminous flux, for which there is one lumen per square meter. Lumen, in turn, is a very specific value. It denotes the luminous flux emitted by a point isotropic source (hence the light is monochromatic). The luminous intensity of this source is equal to one candela per solid angle of one steradian. The unit of illumination is a complex value that includes the concept of "candela". The physical meaning of the last definition is as follows: the intensity of light in a known direction from a source thatemits monochromatic radiation with a frequency of 540 1012 Hz (wavelength lies in the visible region of the spectrum), and the energy intensity of light is 1/683 W/sr.
Light concepts
Of course, all these concepts at first glance look like a spherical horse in a vacuum. Such sources do not exist in nature. And the attentive reader will certainly ask himself the question: “Why is this necessary?” But physicists have a need to compare. Therefore, they have to introduce certain norms that must be guided by. The illumination formula is simple, but a lot can be unclear. Let's break it down.
Index "υ"
Index υ means that the value is not quite photometric. And this is due to the fact that human capabilities are limited. For example, the eye perceives only the visible spectrum of electromagnetic radiation. Moreover, people see the central part of this scale (refers to green color) much better than the marginal areas (red and purple). That is, in fact, a person does not perceive 100% of photons of yellow or blue color. At the same time, there are devices that are devoid of such an error. The reduced values that the illuminance formula operates on (luminous flux, for example) and which are denoted by the Greek letter "υ", are corrected for human vision.
Monochromatic Radiation Generator
At the very basis, as mentioned above, is the number of photons with a certain lengthwaves that are emitted in a certain direction per unit of time. Even the most monochromatic laser has some wavelength distribution. And he certainly has to be on to something. This means that photons are not emitted in all directions. But in the formula there is such a thing as a "point source of light." This is another model designed to unify a certain value. And not a single object of the universe can be called that. So, a point light source is a photon generator that emits an equal number of electromagnetic field quanta in all directions, its size is equal to a mathematical point. However, there is one trick, it can make a real object a point source: if the distance over which the photons reach is very large compared to the size of the generator. Thus, our central star the Sun is a disk, but distant stars are points.
Arbor, well, park
Surely an attentive reader noticed the following: on a bright sunny day, an open area seems much more illuminated than a clearing or lawn closed on one side. Therefore, the seashore is so alluring: it is always sunny and warm there. But even a large clearing in the forest is darker and colder. And the shallow well is poorly lit on the brightest day. This is because if a person sees only part of the sky, fewer photons reach his eye. The coefficient of natural illumination is calculated as the ratio of the flux of light from the entire sky to the visible area.
Circle, oval, angle
All theseconcepts are related to geometry. But now we will talk about a phenomenon that is directly related to the illumination formula and, consequently, to physics. Up to this point, it was assumed that light falls on the surface perpendicularly, strictly downwards. This, of course, is also an approximation. Under this condition, the distance from the light source means the fall in illumination in proportion to the square of the distance. Thus, the stars that a person sees with the naked eye in the sky are either located not so far from us (they all belong to the Milky Way galaxy) or very bright. But if the light strikes the surface at an angle, things are different.
Think of a flashlight. It gives a round spot of light when directed strictly perpendicular to the wall. If you tilt it, the spot will change shape to an oval. As you know from geometry, an oval has a larger area. And since the flashlight is still the same, it means that the light intensity is the same, but it is, as it were, “smeared” over a large area. The intensity of light depends on the angle of incidence according to the law of cosine.
Spring, winter, autumn
The title sounds like the title of a beautiful movie. But the presence of seasons directly depends on the angle at which the light falls at its highest point on the surface of the planet. And at the moment it's not just about the Earth. Seasons exist on any object in the solar system whose axis of rotation is tilted relative to the ecliptic (for example, on Mars). The reader has probably already guessed: the greater the angle of inclination, the fewer photons per square kilometer of surface per second. So thatthe season will be colder. At the moment of the greatest deviation of the planet in the hemisphere, winter reigns, at the moment of the least - summer.
Figures and facts
In order not to be unfounded, here are some data. We warn you: they are all averaged and are not suitable for solving specific problems. In addition, there are directories of surface illumination by different types of sources. It is better to refer to them when making calculations.
- At a distance from the Sun to any point in space, which is approximately equal to the distance to the Earth, the illumination is one hundred and thirty-five thousand lux.
- Our planet has an atmosphere that absorbs some of the radiation. Therefore, the surface of the earth is illuminated with a maximum of one hundred thousand lux.
- In summer, mid-latitudes are illuminated at noon by seventeen thousand lux in clear weather and by fifteen thousand lux in cloudy weather.
- On a full moon night, the illumination is two-tenths of a lux. Starlight on a moonless night is only one or two thousandths of a lux.
- Reading a book requires at least thirty to fifty lux of illumination.
- When a person watches a movie in a cinema, the luminous flux is about one hundred lux. The darkest scenes will have an indicator of eighty lux, and the image of a bright sunny day will “pull” one hundred and twenty.
- Sunset or sunrise over the sea will give an illumination of about one thousand lux. At the same time, at a depth of fifty meters, the illumination will be about 20 lux. Water absorbs sunlight very well.
