Visual comfort

2.2.1 Standard framework

The main standards that regulate acoustic comfort are NF S31-080, EN 3382-3, ISO 22955 and EN 16798.

The first one is a French standard that specifies acoustic requirements according to different levels (standard, efficient, highly efficient) for different types of areas in office buildings.

EN 3382 is an international standard divided in three parts: performance spaces, reverberation time in ordinary rooms, and open plan offices. The third part specifies a measurement method, in which numerical results indicate acoustic performance of open space.

Standard ISO 22955 is a technical guidance to achieve acoustic quality of open spaces, more specifically this document is used for refitting projects, renovation or change/add activities.

Standard EN 16798 provides values to limit the sound pressure level due to mechanical equipment and to set sound insulation requirements for the noise from outside and adjacent rooms.

Lighting sources (sun or light bulb) emit propagating energy, of which a limited range of wavelengths, included between infrared and ultraviolet, is perceptible to the human eye as light. Human perception of light is determined by the amount of radiation energy that enters the eye.

Figure 3 visible light spectrum. Source: Simone M. Matthews - Universal Life Tools

Illuminance is one of the photometric indexes. It permits to measure illuminance level on a work surface, with the aim to understand visual condition for a specific activity. It is the result of the ratio between the luminous flux on a surface and the surface itself.

If illuminance is not homogeneous on the surface the comfort will be not ensured, thus the other important index for visual comfort assessment is illuminance uniformity. Important variations of illuminance can cause annoyance.

Human eyes perceive the surfaces for their luminance, it is the luminous flux emitted or reflected from a lighting surface, thus the photometric measure of the luminous intensity per unit area of light in a given direction. Therefore, it represents how the surface of an object brights, for this reason relevant luminance differences can cause discomfort.

Moreover, glare is caused by an intensity of light in the visual field that is usually greater than the intensity of light that is adapted to the eyes. To assess the discomfort glare caused directly from the luminaires is evaluated

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Lighting sources (sun or light bulb) emit propagating energy, of which a limited range of wavelengths, included between infrared to ultraviolet, is perceptible to the human eye as light. Human perception of light is determined by the amount of radiation energy that enters the eye.

Figure 3 visible light spectrum - Simone M. Matthews - Universal Life Tools

Illuminance is one of the photometric indexes. It permits to measure illuminance level on a work surface, with the aim to understand visual condition for a specific activity. It is the result of the ratio between the luminous flux on a surface and the surface itself.

If illuminance is not homogeneous on the surface the comfort will be not ensured, thus the other important index for visual comfort assessment is illuminance uniformity. Important variations of illuminance can cause annoyance.

Human eyes perceive the surfaces for their luminance, it is the luminous flux emitted or reflected from a lighting surface, thus the photometric measure of the luminous intensity per unit area of light in a given direction. Therefore, it represents how the surface of an object bright, for this reason relevant luminance differences can cause discomfort.

the unified glare rating index.

Correlated colour temperature (CCT) is the measure of light source colour appearance, defined by the proximity of the light source chromaticity coordinated to the blackbody locus, as a single number rather than the two required to specify a chromaticity.

Colour rendering index (Ra) provides information about the quality of the colour rendering of a light source.

In recent years, a great attention has been given to new indexes to evaluate natural lighting, moving toward dynamic daylighting metrics. U.S. Green Building Council codified two metrics indexes in LEED v4, also described in IES_LM-83-12: Spatial daylight autonomy (sDA_300,50%) and Annual sunlight exposure (ASE). They describe daylight performance.

Spatial daylight autonomy defines the percentage of floor area that receives at least 300 lx for at least 50% of annual occupied hours.

The second one, Annual sunlight exposure is the percentage of an analysis area that exceeds a specified direct sunlight illuminance level more than a specified number of hours per year. In particular, ASE_1000,250h is the percentage of an analysis area that exceeds illuminance level of 1000 lx for more than 250 hours per year.

Daylight glare probability represents the vertical illuminance at eye level, related to source luminance size and location, view direction and background luminance (Shen and Tzempelikos, 2014). It is the most recent index used to evaluate glare from daylight, resulted by experimental data in private office spaces involving human test subjects.

Knowing more about light and how to control it is important for its direct influence on health and well-being.

2.3.1 Standard framework

Standards that define visual comfort indexes are: EN 12464, EN 16798, EN 17037, IES_LM-83-12.

EN 12464 provides indexes for electric illuminance in workplaces, defining values to ensure lighting quality and quantity.

Illuminance level required by EN 16798 shall be obtained by daylighting (according to the daylight availability), electric lighting or a combination of

both (calculated only for the occupied hours).

EN 17037 defines indexes to reach, through natural lighting, proper visual level to carry on activities indoor, avoiding glare.

IES_LM-83-12 was created to describe dimensions of daylighting performance. It has the aim to define a consistent calculation methodology that would allow to compare in a consistent manner multiple design alternatives and climatic locations.