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Enciclopedia della luce


Terminology around light

3-phase Tracks

The 3-phase track system consists of an aluminium profile with a length of 1, 2, 3 or 4 m and four electrical conductors, 3 phases and a protective conductor. All three phases can be switched separately. They thus allow simple changes to the lighting and presentation. This creates a functional track system that is just as suitable for accent lighting as it is for illuminating hanging billboards and decorative materials.

Beam angle
  • Spot
    The directional light of the different spot variants is particularly suitable for task and accent lighting. You can use it to highlight certain areas of a room or sales floor, or even to set the scene for a specific product or object. The beam angle depends on the size of the object and the distance to the light source.
  • Flood
    The different flood angles emit a wide beam and are therefore best suited for the basic and general lighting of a room or for illuminating larger areas and objects.
Illuminance/ Lux (lx) =lm/m²

Illuminance is measured in lux (lx) and is the luminous flux falling on a given surface: lx=lm/m². It is one lux when the luminous flux of one lumen uniformly illuminates one square metre of surface.

Illuminance gives no indication of the impression of brightness because this can be perceived differently depending on the area illuminated. This depends on the reflectance values of the room. It makes a difference, for example, whether white or black walls or light or dark furniture are illuminated.


DALI is the abbreviation for Digital Addressable Lighting Interface and, in building automation, is a protocol for controlling lighting control gear, such as switching power supplies, electronic ballasts or electronic power dimmers, which is used in particular in buildings such as offices, shops, restaurants or hotels.


ENEC stands for European Norms Electrical Certification. The symbol is used within the EU for product labelling of electrical appliances. In contrast to CE marking, which each manufacturer can declare himself, ENEC is awarded by independent testing institutes. These testing bodies must be approved by the European Committee for Electronic Standardisation. The ENEC mark ensures that the product complies with EN safety standards and requirements, that the product is retested every two years, that the manufacturer operates with a quality system according to ISO 9000 and that the manufacturer has documented production control, e.g. through manufacturing inspections.

Colour rendering index/ Ra or CRI (Colour Rendering Index)

The colour rendering index describes the effect that the light of a lamp has on coloured objects. The higher this value, the more optimally and faithfully the colours are reproduced in the respective light. 100 stands for the best value. Natural light/sunlight therefore has a colour rendering index of 100 Ra. Halogen lamps are between 95-100 Ra, LEDs (depending on the light colour) between 70-92, energy-saving lamps and fluorescent lamps between 80-90 Ra. Indoors, where people work or spend longer periods of time, the Ra value should not fall below 80.

Example in connection with light colour:
The value 830 indicates a combination of Ra and light colour
The 1st digit 8(0) stands for an Ra > 80. The 2nd and 3rd digits 30(00) provide information on the light colour, which in this example is 3000K.

  • Class 1A
    Luminaires and lamps with an Ra/CRI value greater than or equal to 90 are assigned to class 1A. Their colour rendering is excellent and comes close to that of daylight. These light sources are suitable for areas where colour rendering is very important, such as sales areas, designers' and graphic artists' workplaces.
  • Class 1B
    Luminaires and lamps with an Ra/CRI value between 80 and 89 are classified as class 1B. Their colour rendering is good to very good. These light sources are suitable for areas where colour rendering is important, e.g. in living rooms or offices.
  • Class 2A
    Luminaires and lamps with an Ra/CRI value between 70 and 79 are classified as class 2A. Their colour rendering is medium to good. These light sources are suitable for areas where colour rendering is of secondary importance, e.g. in warehouses and outdoor areas.
  • Class 2B/3/4
    Luminaires and lamps with an Ra/CRI value lower than 70 are assigned to classes 2B, 3 or 4. Their colour rendering is very inaccurate. These light sources are not suitable for areas where people spend long periods of time, but only for areas where lighting is necessary but colour rendering is not important.
Colour tolerance (Binning & MacAdam)

In the production of LEDs, there are unavoidable tolerances in colour and brightness. Especially deviations in light colour are easily perceived by the observer. The chromaticity coordinates of a particular colour can be precisely described by x and y coordinates in the CIE colour diagram. MacAdam ellipses describe an area in the CIE colour diagram. These ellipses are used to distinguish between two light sources. Steps indicate the colour distance from the x/y coordinates. Light sources with a colour distance of a 3-step MacAdam ellipse differ less than two light sources whose colour distance corresponds approximately to a 5-step MacAdam ellipse. Particularly in lighting applications where individual light sources are in close proximity and can be seen at the same time, attention should be paid to small colour gaps.

The process of colour class formation in LED production is called "binning". Here, LEDs are sorted into so-called "bins" in order to guarantee the most uniform light colour possible.


Luminance is a measure of the brightness impression of a self-luminous light source or an illuminated surface (visible light) and is measured in candela per square metre.

Luminance = candela / area (cd/m²)

LOR = Light Output Ratio / Effizienz

The operating efficiency of a luminaire is the ratio of the luminous flux of the luminaire to the luminous flux of the lamp and thus describes the efficiency of the luminaire. The reflector geometry as well as thermal conditions have an influence on the LOR. The measured luminous flux (lm) is divided by the measured input power (W) of the same luminaire. Luminous efficacy is expressed in lumens per watt (lm/W) and can be used to assess energy efficiency, with limitations.

Luminous efficacy = efficiency of the lamp lm/W

Luminous efficacy is the measure of the efficiency and thus economy of a light source. It describes the luminous flux in lumens (lm) that a lamp produces per watt (W) of power input. The higher the ratio of lumens per watt, the better the lamp converts the energy input into light.

Light colour / Kelvin (K)

Humans experience their environment not only as light and dark, light and shadow, but also through colours. Light colour is the spectral composition of light as it is produced by a light source or reflected by a body.

Candle (1,500 Kelvin) and blue sky (10,000 Kelvin) serve as reference values. The higher the colour temperature (Kelvin), the whiter the light colour. The lower, the warmer and more pleasant the light.

The light colours of lamps and luminaires are divided into 3 groups:

  • Warm white: < 3.300 K. This light colour is perceived as pleasant and is particularly suitable for areas where the focus is on cosiness, such as living rooms, restaurants or bars.
  • Neutral white: 3.300–5.300 K. This light colour is considered activating and creates a "businesslike" atmosphere. It is mostly used in Büros and work areas.
  • Daylight white: > 5.300 K. This light colour has a "clinical" effect and creates very good visual conditions. It is considered to promote concentration and is particularly suitable for areas where concentration is required, such as offices, production halls and schools.

However, under light colour you will often find a value such as 830 or 940. What does this mean? Here, a combination of colour rendering index and light colour is shown.

Light colour 830 therefore means:
1st digit: 8(0) = Ra > 80
2nd +3rd digit: 30(00) = Light colour 3000K

Light intensity / Candela (cd)

Light intensity is measured in the unit candela (cd) and refers to the light power emitted by a light source in a specific direction.

Light intensity distribution / light distribution curve

The spatial distribution of the luminous intensity of a light source results in a three-dimensional representation. The section through this light intensity body results in the light intensity distribution curve, which describes the light intensity distribution in a plane. The luminous intensity is usually entered in a polar coordinate system as a function of the radiation angle. Depending on the shape and symmetrical properties of the luminous intensity distribution of a luminaire, a distinction is made between deep-beam, wide-beam, symmetrical and asymmetrical luminous intensity distributions.

Luminous flux / Lumen (lm)

Luminous flux is measured in the unit lumen (lm). Luminous flux describes the luminous power emitted by a light source in all directions.

Impact strength/shock resistance

Impact resistance is defined as the protection of a housing, e.g. a luminaire, against mechanical stress from outside, e.g. protection against impact. There are 11 levels, from 0 to 10.

IK00 means no protection, IK10 protects up to an impact energy of 20 joules.

Protection class

The protection class of a luminaire indicates how well a luminaire is protected against contact, foreign bodies and water. This is indicated by the IP numbering system, which is used for many different electrical appliances. It consists of two numbers. The first refers to protection against the ingress of foreign bodies, such as dust. The second digit refers to protection against moisture or water.

  • First digit : Protection against contact and foreign bodies
    0: No protection
    1: Protection from solid foreign bodies ≥ 50 mm
    2: Protection from solid foreign bodies ≥ 12,5 mm
    3: Protection from solid foreign bodies ≥ 2,5 mm
    4: Protection from solid foreign bodies ≥ 1 mm
    5: Dust protected
    6: Dust-tight
  • Second digit : Protection against moisture
    0: No protection
    1: Protection against vertically falling dripping water
    2: Protection against dripping water
    3: Protection against spray water
    4: Protection against splash water
    5: Protection against water jets
    6: Protection against strong jets of water
    7: Protected against double immersion
    8: Protected against permanent immersion

Common combinations/examples:
IP20 Minimum requirement for interior luminaires
IP44 Splash water protected, e.g. house number light
IP54 e.g. bollard luminaire (outdoor area)
IP65 e.g. damp-proof diffuser luminaire, recessed luminaires bathroom (wet area)

Protection class

The protection class indicates the measures taken in the construction of the luminaire to avoid electric shock. The construction and operating mode determine this protection class. Especially with metal housings, a malfunction or short circuit can cause a life-threatening situation. The scope of protective measures against electric shock is described in three protection classes according to DIN VDE 0711:

  • Class I
    All electrically conductive housing parts of the luminaire or the device are firmly connected to the protective conductor system. The protective conductor connection of the housing is dimensioned in such a way that no permanent dangerous contact voltage occurs at the housing and that the fuse or a residual current circuit breaker blows and switches the circuit voltage-free.
  • Class II
    Luminaires or devices with protection class II have double or reinforced insulation.
    If they have an electrically conductive surface or touchable parts, these are separated from live parts by double or reinforced insulation. In most cases, these devices do not have a connection to the protective earth conductor.
  • Class III
    Luminaires or devices with protection class III use safety extra-low voltage (SELV) or functional extra-low voltage with electrically safe isolation (PELV) and may therefore only be connected to corresponding SELV or PELV power sources of 42 volts. These include safety transformers or batteries. Luminaires or devices with PELV have double or reinforced insulation between the mains connection and the conductive parts.

The abbreviation UGR stands for Unified Glare Rating. The UGR value is a dimensionless indicator that says something about the degree of psychological glare of a lighting system in the interior. UGR values are defined in levels for the range from 10 to 30. The levels defined in accordance with DIN EN 12464-1 are 13, 16, 19, 22, 25 and 28 and express the statistical glare perceived by a large number of observers. The lower the UGR value, the fewer observers experience direct glare. Different activities have different regulations with regard to glare:

  • Technical drawing: UGR≤16
  • Reading, writing, classroom work, computer work, control work: UGR≤19
  • Working in industry and crafts, reception: UGR≤22
  • Rough work, stairs: UGR≤25
  • Hallways: UGR≤28

In general, the UGR value must not be greater than 19 in rooms with VDU and/or Büro workstations.


UV-C light is an electromagnetic radiation and cannot be perceived by the human eye. The very high-energy radiation has a wavelength of 100-280 nanometres and triggers a photochemical reaction. Depending on the irradiation dose, UV-C light leads to the destruction or damage of bacteria and fungal spores. For this reason, it is also produced artificially and used specifically for disinfection. Known areas of application of UV-C radiation are surface disinfection, for example in laboratories, room air disinfection or water treatment. However, UV-C radiation can directly or indirectly damage genetic material and cause other health problems to the eyes and skin, which is why it is essential to observe the safety instructions when using UV-C equipment.


Zigbee is a specification for wireless networks with low data volume, e.g. in lighting technology. It is a complete loT solution with which intelligent objects can work together.

Zigbee certified products can connect and communicate with each other using the same IoT language. Zigbee is one of the most widely used smart home technologies in the Internet of Things and serves smart home systems such as Amazon Echo Plus, Philips Hue or Ikea.