The Indoor Lighting Standard, SFS-EN 12464-1:2011

Illuminance

The SFS-EN 12461-1:2011 standard specifies the minimum required illuminance levels for the task area and its surroundings (see Table 1). The minimum illuminance is 50 lx for walls and 30 lx for ceilings. Illuminance in the surrounding areas must be no less than a third of the illuminance in the immediate vicinity of the task area. This improves the luminance ratio in the space, increasing visual comfort and performance. The illuminance uniformity value must be no less than 0.4 in the immediate vicinity and no less than 0.1 in the background. Examples of lighting requirements for spaces, areas, tasks, and activities are presented in Table 2.

TABLE 1: Luminance ratios for a task area and its immediate vicinity

TABLE 2: Examples of lighting requirements for spaces, areas, tasks, and activities

For indoor activity areas, the mean cylindrical illuminance must be at least 50 lx and the uniformity no less than 0.1, as calculated 1.2 m above floor level. For spaces where visual communication is especially important, such as offices and education premises, the maintained mean cylindrical illuminance should not be less than 150 lx, with uniformity no less than 0.1.

Modelling

Modelling, which is the balance between diffuse and directional lighting, is another aspect of lighting that should be considered in the design of lighting systems. The overall appearance of a space improves when its structural features, along with people and objects in the room, are illuminated such that the shape and texture appear clear and pleasant.  Lighting that is too directional may give rise to sharp, harsh shadows. On the other hand, lighting that is overly diffuse results in the objects and space appearing too dull and bland, making the room and its details difficult to perceive. The ratio between cylindrical and horizontal illuminance on the reference plane provides information on the modelling. A value between 0.3 and 0.6 for luminaires placed at regular intervals indicates that the modelling is good.

Glare

For visual comfort, the direction of light, in relation to the shape and location of an object, must be such that it does not give rise to discomfort or disability glare. Glare may occur when the illuminance level or luminance ratio in the visual field is not ideal or changes too rapidly. The standard uses UGR values, ranging from 10 to 28, to describe discomfort glare. Typically, UGR values are defined with lighting design software, which calculates a luminaire’s UGR index value on the basis of the information provided by the manufacturer. The SFS-EN 12464-1:2011 standard specifies maximum UGR values for various indoor applications.

Colour properties

In the design of lighting, consideration should be given to the light source’s colour appearance and colour rendering, so that the colours of various objects, surfaces, and people in the space appear natural and correct.  Colour appearance is influenced by illuminance, the colours of the space and furnishings, climate, and the use of the space.

TABLE 3: A lamp’s colour appearance as a function of colour temperature

Colour rendering describes the ability of a light source to show the colours of objects faithfully and naturally. The colour rendering ability is dependent on the light spectrum emitted by a light source, as, in practice, a light source reveals the colours it emits. Good colour rendering shows objects in their natural colours and produces pleasant lighting. Light sources’ colour rendering ability is measured with R_a index values (see Table 4). The index is a percentage (0–100%) indicating how accurate a particular light source is in rendering colour when compared to the natural light spectrum. The SFS-EN 12464-1:2011 standard specifies minimum values for colour rendering for various indoor spaces, tasks, and activities.

TABLE 4: Colour rendering classes