2.5.2. Requirements to work area illumination

Requirements to work area illumination listed below provide visual comfort and prevent occupational diseases and accidents:

• workplace illumination should be appropriate to visual task (category);

• illumination should not make a glare from the source of light or surrounding objects;

• illumination in work area should be uniform and stable to avoid frequent eyes’ re-adaptation;

• sharp and deep shadows are not allowed at the work plane;

• contrast of illuminated objects should be sufficient;

• illumination should not be a hazardous or harmful;

• illumination should be simple, reliable, reasonable and aesthetic.

2.5.3. Types of work area illumination

Work area illumination can be performed as natural or artificial. Sunlight, horizon, moon, and stars make natural illumination, electric radiant sources - lamps make artificial one, there’s also combined illumination including both previous types.

Natural illumination can be arranged as side, overhead and combined lighting.

Side lighting: the use of daylight apertures on the walls of buildings to provide daylight on tasks. It can be one-sided and two-sided.

Overhead lighting: daylighting concepts in the roof of a building that provide light from above to illuminate horizontal, sloped, or vertical work planes.

Combined lighting comprises overhead and side one.

Artificial illumination can be performed as general and combined lighting.

General illumination is lighting system, in which luminaries are set in overhead space of the area (as lowest 2.5 m above the floor) uniformly (general uniform lighting) or focused over the work planes (general focal lighting).

Combined lighting comprises general and focal one. It provides high visual acuity. Luminaries focusing their luminous flux directly in work plane create focal lighting. Application of only focal lighting in work areas is not recommended at all to prevent occupational accidents and diseases.

Depending on functional purpose artificial illumination is classified as work, emergency, evacuation, security and stand-by lighting.

Work lighting provides visibility needed for production, moving, transporting and is obligate for all occupational areas.

Emergency lighting is aimed at preventing explosion, fire, injuries, damages etc, when the work lighting is occasionally shutdown.

The purpose of evacuation lighting is to assist evacuation in condition when work lighting is off. It’s mounted in passages of personality, in areas with personality, which may count over 100 persons present there simultaneously, in stairwells, in occupational areas with personality over 50 persons.

Security lighting is set at perimeter of secured territory.

Stand-by lighting is foreseen in overtime.

2.5.4. Natural illumination

It is evident that there is a coherent relationship between natural light and health in humans. Each of the effects of light upon mammalian tissue may be classified as being direct or indirect depending on whether its immediate cause is a photochemical reaction occurring within that tissue or a neuroendocrine signal generated by a photoreceptor. One of the best known direct effects of light on man is that of the stimulation of vitamin D synthesis in the skin and subcutaneous tissue by sunlight. The second group of effects are the indirect ones, those whereby light exerts an effect by way of the eyes on various metabolic, hormonal and organic functions. Circadian rhythms are entrained by the light-dark cycle zeitgeiber in this way.

However, prediction of natural illumination is complicated owing to its varying during a day or year or weather, not uniform lighting the work area, possible glare.

Particularly, natural illumination is impaired by the following factors: light climate, window area and its orientation, glazing visual transmittance, color of walls, floor and ceiling.

Natural illumination is evaluated by daylight factor (DF). DF is a relative measure of daylight illuminance at an interior point or plane expressed as the ratio of the illuminance on the given plane (E_in) to the simultaneous exterior illuminance (E_out) on a horizontal plane from the whole unobstructed sky. Direct sunlight is excluded from both interior and exterior values of illuminance.

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Illuminance inside the work area is measured in the point which is located depending on type of lighting. For one-sided lighting it’s found in crossing line of plane making central vertical section of the area and another horizontal plane, which is at the height of work plane 0.8 m at the distance 1 m from the wall opposite to window. For overhead lighting – in the crossing line of plane making central vertical section of the area and another horizontal plane, which is at the height of workplace 0.8 m at the distance 1 m from the most dark wall.

DF standards are provided by “Construction Regulations” (SNiP II-4-79).

Prediction of natural lighting is associated with calculation of window opening (windows, skylights) area and its assessment against DF standard.

Window opening area is calculated by the formula:

for side lighting,

for overhead lighting,

where S_w, S_s – window or sky-light areas; S_a – work area; DF_st – DF standard; h_w, h_s – window-to-wall ratio; d – shading from outdoor obstruction; ₀ – effective aperture; r₁, r₂ – internally reflected component.

DF standard comprises visual task and light climate:

,

where m – light climate factor in the light zone where building is situated; С – sun climate factor.