Is there a difference between brightness and light? Luminous flux is the light energy emitted by a point source. Since it depends on the distance, it is expressed in spatial angles.

Lumen - a unit of measurement of the power of light radiation, which is estimated by the light sensation in the human eye.

In what units is the luminous flux measured? The unit of measurement of luminous flux can be considered as the total amount of light. For example, a 40 W incandescent lamp will create a luminous flux corresponding to 415 lumens, luminous - a flux of 3200 lumens. Put any optical system around the light source, the amount of light (lumens) will be the same. Thus, if the number of lumens is not written on the undirected light source, it is not clear how it will illuminate.


  • 1 Illumination and brightness
    • 1.1 The difference between the concepts of brightness and light
  • 2 Lux and candela units
  • 3 Photometer
    • 3.1 Safe light flow at work
    • 3.2 Luminous flux and museum exhibits
    • 3.3 Luminous flux in horticulture and crop production

Illumination and brightness

Illumination is the amount of light, it

determines the amount of light, which falls on a particular surface area of ​​the body. It depends on the length of the light wave, because the human eye perceives differently the brightness of different lengths of light waves, in other words, different colors.

Illuminance is calculated for different wavelengths separately. People perceive as the brightest colors:

  • green - light with a wavelength of 550 nanometers;
  • yellow orange. Located next to him in the spectrum.

Light emanating from red, blue and purple has a short or long wave, so they are perceived as darker. The concept of light is often correlated with the concept of brightness.

When lighting the area with the same lamp, a large area will be less illuminated than a small one.

The difference between the concepts of brightness and light

Photometer measures the amount of lightRussian language gives two answers to the question of what is brightness. Brightness means the characteristics of luminous bodiesthat is a physical quantity. It also defines a subjective concept that depends on many factors, for example:

  • features of the structure of the human eye;
  • the amount of light in the room.

The less light in the environment, the brighter the light source seems to be. It is necessary to distinguish brightness with light and remember the following:

  • brightness is the light that is reflected from the surface of a luminous object;
  • Illumination is the light that falls on the illuminated surface.

In astronomy, brightness includes two concepts where stars emit and planets reflect. In this science, stellar brightness is measured by photometric scale, with the greater brightness of the star correlate with a smaller value. The brightest stars have a negative magnitude.

Lux and candela units

Unit of measurement of luminous flux - lumenThe unit of measurement of brightness (candela per square meter) is used for applied or physiological purposes.

The unit of measure is used to calculate the level of illumination. One suite equals one lumen per square meter. Also, to measure the light used foot candela. She is approached in the field of cinema and photography and some others. The foot is present in the title because the foot candela means candela square foot illuminationmeasuring in the range of one foot.


What is Lumen and how to measure it?The photometer is a device measuring light. The light enters the photo detector, then is converted into an electrical signal and measured. There are photometers operating on a different principle. Basically photometers show the light level in suites, but there are those who use other units. Those photometers, also called exposure meters, are involved in determining shutter speed and aperture, thereby helping photographers and cameramen. In addition, photometers are used to determine the level of safe illumination in other areas, for example, in plant growing, in museums, where it is necessary to maintain the desired illumination.

Safe light flow at work

When working in a dark or dimly lit room, various health problems may arise, be it a deterioration of vision, depression or other physiological and psychological disorders. For this reason, the workplace, within the framework of labor protection regulations, includes requirements for minimum safe illumination. The final measurement result, which gives the photometer, includes the area of ​​propagation of light. These indicators provide sufficient illumination of the entire room.

Luminous flux and museum exhibits

Units of lightFrom the light and power flow from the light source depends on the speed with which the exhibits of the museum will fade and fade. Museum workers are working to determine the lighting of exhibits. This is done in order to ensure a safe amount of light flux on the museum units, as well as to ensure a sufficient level of illumination to visitors during viewing exhibit.

The light level can be measured with a photometer, which is not easy to implement, since it should be installed as close as possible to the exhibit, and this requires removing the protective glass, turning off the alarm and obtaining permission. This task is facilitated by another method that is often used by museum staff. Instead of a photometer, a camera is used, which is not a substitute for a photometer in situations where more accurate measurements of the problem found with the lighting, but in order to identify a deviation from the norm it is quite enough

Determine the exposure of the camera can be based on indications of the level of illumination. The level of exposure light is easy to determine by simple calculations. Museum staff resort to the formula or use the tablewhere exposure is in units of light. When making calculations, you should not forget that the camera absorbs a certain amount of light, so you should take this into account.

Luminous flux in horticulture and crop production

One lux is equal to one lumen per square meterBefore you provide the plant with the light that is needed for photosynthesis, you need to know how much it requires for each crop. Gardeners and growers know this. They measure the light level to make sure that each plant receives the amount of light it needs. Often photometers are used for such procedures.

Photometers are also widely used in laboratory practice. For example, the spectrum of samples is determined by which the chemical composition is determined. A special class of such devices is a flame photometer. is he detects alkali metals in samples, such as sodium, lithium, potassium. To detect them, you need to burn the sample at a high temperature and use a photometer to analyze the spectrum of the flame. This problem is solved in other ways much more difficult.

Modern photometers convert light radiation into electrical pulses, they are recorded on the principle of an ammeter and a voltmeter, and then converted into a computer format.

A photometer is a device that covers many areas of knowledge, such as chemistry, molecular biology, physics, materials science, and others. The photometer is widely used in industry, in laser and optical products. In addition to the chemical laboratory, the photometer is used in forensic laboratories.

Thus, from the foregoing, you learned about the units of light that lamps are better to buy with the specified number of lumensthat the concepts of light and brightness differ, and the amount of light can be measured with a special device.