About light

One of the first questions that should be posed when planning a lighting installation is: ‘What are the primary functions of the lighting?’ The answer to this question will depend on the sort of space that needs lighting, and the sort of job that needs to be done in said space. In rooms or areas where visual tasks have to be carried out, the so-called ‘workspaces’, the primary function of the lighting is of course to improve the visual prestation.

Lighting in corridors inside buildings must be sufficiently safe so that even in darkness, safety is guaranteed. In places meant for social contact however, visual prestation is not a priority and the emphasis is almost completely on visual comfort. Other functions of light include medical functions or the beautification of an area.

Fixture efficiency

The fixture efficiency is the quotient of the luminous flux emitted from the fixture and the flux emitted from the accessory lightsource(s). The energy efficiency of a lamp is quotient of the emitted rays of light and the power that is used to fuel these.

Luminous flux F

All radiation energy emitted by a lightsource that is perceived by a human eye is the luminous flux F. Simply put, the luminous flux is the measure for the amount of visible radiation (=light) a lightsource emits. The unit that is used is lumen (lm).

Evenness

The evenness is the ratio between the minimal and average illuminance on a surface.

Colour temperature

Materials emit light, the colour of this light is dependent on the temperature. Every given temperature has an accesory colour: the colour temperature. The colour temperature is measured with degrees Kelvin (K). This matches the colour of the light that a metal alloy will emit at certain temperatures. It is a way to precisely measure different kinds of colours and their shades.

White lightsources can be divided into three categories based on the colour of the light.

Colour temperatureColour of the light
< 3300 KWarm (red-like white)
 3300 – 5300 KMedium (white)
> 5300 KCool (blue-like white)
 2000 – 2500 KYellow-white
 2500 – 2900 KExtra warm white
 2900 – 3300 KWarm white
 3300 – 5000 KNeutral white
> 5000 KCool white

To make sure that light is of good quality, the colour temperature of the light should be relative to the level of illuminance. Experience has learned us that it is better to use a higher colour temperature for higher levels of illuminance. So, the higher the level of illuminance, the ‘whiter’ the colour of the lightsources should be.

Colour rendering

Colour rendering has to do with the amount of lightfrequencies that are present in the visible spectrum of light. When all frequencies are present, colour rendering is 100 per cent. All colours are clearly visible when this is the case. Once frequencies are missing, colours are perceived in a dinimished fashion. This is expressed in a coefficient: the colour rendering index (CRI).

As a rule, artificial light should give the human eye the possibility to correctly see colours, just like regular daylight. This of course depends on both the place and the function of the light. The CRI measures the similarity between the colour of an object (as perceived by the eye) and that of a light source. To calculate the CRI-values, eight test colours are defined and subsequently lit using the light source. The degree in which the colours differ from what they are when lit using the light source determines the CRI values. A lightsource with a CRI value of 100 shows all colours exactly as they are. In case of a low CRI value, colours are not visible correctly.

Luminance L 

The luminance L of a lightsource or a lit surface expresses the degree of brightness perceived by the eye. The corresponding unit of measurement is candela per square meter.

Luminance

Luminance is a concept that is mainly used to characterize relations between different degrees of brightness in indoor areas. A room that is lit very monotonously, meaning that different parts of the room are lit to more or less the same extent, is often experienced as dull and unstimilating by people that work there. In museums however, an equal distribution of luminance is preferable to focus the attention on the objects on display. When brightness contrasts are too great in a visual environment, the eye needs to constantly adjust to these contrasts. This can lead to exhaustion and, especially in work environments, to a loss of productivity. For this reason a rule of thumb for lighting work environments is that the luminance-ratio between the visual job, the direct environment of the visual job and the further environment should be approximately 10:3:1.

Illuminance E

Unit of measurement: lux [lx]. The illuminance is the luminance per surface. A luminance of 1 lux arises when a luminance of 1 lm is equally distributed over a surface of one square meter.

Diminishing light output

The moment a system of lighting has been made operational, the average light output of this system will eventuall diminish over time. This diminishment is caused by:

  • The light output of nearly all lamps decreases as time passes by
  • Lamps that have reached the end of their lifespan start to fault
  • The fixtures are subject to pollution
  • The walls, that through reflection indirectly contribute to the degree of brightness in the workspace, get less clean

The degree in which light output diminishes because of time strongly depends on the type of lamp. For example, a lightbulb will lose its worth far quicker than an LED. The degree of pollution on fixtures and walls is highly dependent on the type of work that is executed in the room. In a garage a lot more pollution will occur than in a regular office.

The degree of light output thus depends on:

  • The type of light source
  • The type of activities

The demands on the average light output are minimal requirements according to European standards.

Reflection

Reflection on ceilings, floors and walls, dependant on the size of the room and the chosen light source, more or less contribute to the light output on the workfloor. To calculate this, the degree in which these surfaces reflect light is calculated.

The reflection is the ratio between the reflected luminous flux to the incoming luminous flux.

Blindness

Blindness is the feeling that is caused when the degree of luminance that is experienced by the eyes is far greater than that what the eyes are used to, which can be experienced as unpleasant. Blindness usually manifestates in two different ways, which can be experienced seperately or both at once. The first is masking blindness, which leads to bad performance completing visual tasks, while making it difficult to see objects. The second is known as hindering blindness, which creates a feeling of unease, without necessarily diminishing the perception of objects. Blindness can occur directly or through a reflection. Direct blindness occurs for example if you look into a bright fixture directly. Blindness through reflection occurs when a ray of light reaches the eyes through a reflecting surface. In the case of indoor lighting, hindering blindness is usually a bigger problem than masking blindness. The feeling of unease has the habit of increasing as time passes by, which contributes to tension and exhaustion. Measures taken to limit hindering blindness will usually also diminish masking blindness.

About light

One of the first questions that should be posed when planning a lighting installation is: ‘What are the primary functions of the lighting?’ The answer to this question will depend on the sort of space that needs lighting, and the sort of job that needs to be done in said space. In rooms or areas where visual tasks have to be carried out, the so-called ‘workspaces’, the primary function of the lighting is of course to improve the visual prestation. Lighting in corridors inside buildings must be sufficiently safe so that even in darkness, safety is guaranteed. In places meant for social contact however, visual prestation is not a priority and the emphasis is almost completely on visual comfort. Other functions of light include medical functions or the beautification of an area.

Fixture efficiency

Het armatuurrendement is het quotiënt van de lumestroom die uit het armatuur komt en de lumestroom van de er in toegepaste lichtbron(nen).De specifieke lichtstroom van een lamp is het quotiënt van de uitgezonden lichtstroom en het door de lamp verbruikte vermogen. 

Luminous flux F

Alle stralingsenergie die door een lichtbron wordt afgegeven en door het oog wordt waargenomen is de lichtstroom F. Simpeler gezegd is de lichtstroom de maat voor de hoeveelheid zichtbare straling (= licht) die een lichtbron uitzendt. De eenheid die hiervoor gehanteerd wordt is lumen (lm).

Evenness

The evenness is the ratio between the minimal and average illuminance on a surface.

Colour temperature

Materialen stralen licht uit waarbij de kleur afhankelijk is van de temperatuur. Voor elke gegeven temperatuur is er een kenmerkende kleur: de kleurtemperatuur. De kleurtemperatuur wordt uitgedrukt in hoeveelheid graden Kelvin. Deze komt overeen met de kleur van het licht dat een bepaalde metaallegering bijeen bepaalde temperatuur uit gaat zenden. Het is een manier om heel precies de verschillende soorten kleuren en kleurschakeringen aan te geven. White lightsources can be divided into three categories based on the colour of the light.
Colour temperature Colour of the light
< 3300 K Warm (red-like white)
 3300 – 5300 K Medium (white)
> 5300 K Cool (blue-like white)
 2000 – 2500 K Yellow-white
 2500 – 2900 K Extra warm white
 2900 – 3300 K Warm white
 3300 – 5000 K Neutral white
> 5000 K Cool white
To make sure that light is of good quality, the colour temperature of the light should be relative to the level of illuminance. Experience has learned us that it is better to use a higher colour temperature for higher levels of illuminance. So, the higher the level of illuminance, the ‘whiter’ the colour of the lightsources should be.

Colour rendering

Colour rendering has to do with the amount of lightfrequencies that are present in the visible spectrum of light. When all frequencies are present, colour rendering is 100 per cent. All colours are clearly visible when this is the case. Once frequencies are missing, colours are perceived in a dinimished fashion. This is expressed in a coefficient: the colour rendering index (CRI).

As a rule, artificial light should give the human eye the possibility to correctly see colours, just like regular daylight. This of course depends on both the place and the function of the light. The CRI measures the similarity between the colour of an object (as perceived by the eye) and that of a light source. To calculate the CRI-values, eight test colours are defined and subsequently lit using the light source. The degree in which the colours differ from what they are when lit using the light source determines the CRI values. A lightsource with a CRI value of 100 shows all colours exactly as they are. In case of a low CRI value, colours are not visible correctly.

Luminance L 

The luminance L of a lightsource or a lit surface expresses the degree of brightness perceived by the eye. The corresponding unit of measurement is candela per square meter.

Luminance

Luminance is a concept that is mainly used to characterize relations between different degrees of brightness in indoor areas. A room that is lit very monotonously, meaning that different parts of the room are lit to more or less the same extent, is often experienced as dull and unstimilating by people that work there. In museums however, an equal distribution of luminance is preferable to focus the attention on the objects on display. When brightness contrasts are too great in a visual environment, the eye needs to constantly adjust to these contrasts. This can lead to exhaustion and, especially in work environments, to a loss of productivity. For this reason a rule of thumb for lighting work environments is that the luminance-ratio between the visual job, the direct environment of the visual job and the further environment should be approximately 10:3:1.

Illuminance E

Unit of measurement: lux [lx]. The illuminance is the luminance per surface. A luminance of 1 lux arises when a luminance of 1 lm is equally distributed over a surface of one square meter.

Diminishing light output

The moment a system of lighting has been made operational, the average light output of this system will eventuall diminish over time. This diminishment is caused by:
  • The light output of nearly all lamps decreases as time passes by
  • Lamps that have reached the end of their lifespan start to fault
  • The fixtures are subject to pollution
  • The walls, that through reflection indirectly contribute to the degree of brightness in the workspace, get less clean
The degree in which light output diminishes because of time strongly depends on the type of lamp. For example, a lightbulb will lose its worth far quicker than an LED. The degree of pollution on fixtures and walls is highly dependent on the type of work that is executed in the room. In a garage a lot more pollution will occur than in a regular office. The degree of light output thus depends on:
  • The type of light source
  • The type of activities
The demands on the average light output are minimal requirements according to European standards.

Reflection

Reflection on ceilings, floors and walls, dependant on the size of the room and the chosen light source, more or less contribute to the light output on the workfloor. To calculate this, the degree in which these surfaces reflect light is calculated. The reflection is the ratio between the reflected luminous flux to the incoming luminous flux.

Blindness

Blindness is the feeling that is caused when the degree of luminance that is experienced by the eyes is far greater than that what the eyes are used to, which can be experienced as unpleasant. Blindness usually manifestates in two different ways, which can be experienced seperately or both at once. The first is masking blindness, which leads to bad performance completing visual tasks, while making it difficult to see objects. The second is known as hindering blindness, which creates a feeling of unease, without necessarily diminishing the perception of objects. Blindness can occur directly or through a reflection. Direct blindness occurs for example if you look into a bright fixture directly. Blindness through reflection occurs when a ray of light reaches the eyes through a reflecting surface. In the case of indoor lighting, hindering blindness is usually a bigger problem than masking blindness. The feeling of unease has the habit of increasing as time passes by, which contributes to tension and exhaustion. Measures taken to limit hindering blindness will usually also diminish masking blindness.
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