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Cheat sheet of light engineering terms

  • 20 April 2018 10:12:00
  • Views: 1005

When choosing fixtures, you need to focus not only on the design trends, but also on the technical characteristics. The functionality of the room directly depends on the lighting fixtures, therefore we offer a short crib of terms that will help to communicate with light engineering in one language.

Visible and optical radiation

The visible radiation that a person perceives is concentrated in the spectrum of electromagnetic waves from 380 to 760 nm. To this spectrum is added ultraviolet (UV), which has a biological effect and is used for the healing, and infrared radiation (IR), which produces thermal effects.

Light flux

This characteristic is the most important when choosing an illuminator. It determines the power of visible radiation exposure to the human eye. The value is measured in lumens (lm).

Yes, light flux:

• incandescent lamps E27 75 W = 935 lm;

• Halogen G9 at 75 W = 1100 lm;

• luminescent T5 at 35 W = 3300 lm;

• warm metal-halogen G12 at 70 W = 5300 lm;

• warm LED E27 9.5 Watts = 800 lm.


The lumen corresponds to the light flux from the light source, which was measured under reference conditions.


The illumination (E) is measured in lux (lx) and is determined by the formula: E = F / A, where A is the area. This indicator is the ratio of the light flux that falls on the surface element to the area of ​​this element.

The power of light

The force of light (I) is the magnitude of light energy, which is transmitted in a definite direction per unit time. It is calculated according to the formula: I = F / ω and is measured in candles (cd). So, the average light intensity of a 100W incandescent lamp is about 100 cd.

There is another important characteristic when choosing lamps - the curve of the force of light (KSS). This is the distribution of the force of light in space.


Brightness (L) or light density is associated with a level of visual sensation (visual comfort). Measured in cd / m2. A person, in absolute darkness, reacts to the brightness of one millionth of a cd / m2. The discomfort causes a light flux with a brightness above 500 cd / m2.

Light output

Speaking about the energy-efficiency of a light source, you need to pay attention to the luminous efficiency (H). This is the ratio of the light flux of the lamp to its power. Unit of measurement - lm / W.

The higher the light output, the more energy is saved. If you replace the incandescent lamp 7-22 lm / w with luminescent (50-90 lm / W), the power consumption will be reduced by 5-6 times, with the level of illumination not changed.

Color temperature

The color temperature (Tc) is related to the color of the light sources and the color tonality of the illuminated space. Measured in Kelvin (K).

• Flame of candle - 1900 K.

• Incandescent lamp: 2500-3000 K.

• Fluorescent lamps: 2700 - 6500 K.

• Sun: 5000-6000 K.

• Cloudy sky: 6000-7000 K.

• Clear day: 10,000 - 20,000K

Color rendering index

The color rendering index (Ra, CRI) is the degree of reproduction of colors of various materials when they are illuminated by a light source, when compared with a reference source. The maximum value is Ra = 100. Comfortable for the human eye value CRI = 80-100 Ra.

• Ra = 90 and more - very good (color rendering 1A)

• Ra = 80-89 - very good (degree of color rendering 1B)

• Ra = 70-79 - good (degree of color rendering 2A)

• Ra = 60-69 - satisfactory (degree of color rendering 2B)

• Ra = 40-59 - sufficient (degree of color rendering 3)

• Ra = less than 39 - low (color rendering 3)


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