Types of lighting

Direct lighting (see figure). The luminaires’ luminous flux is directed straight onto the visual task and thus achieves elevated profitability. Reflected glare can be avoided if the luminaires are placed above the sides of the workstations and parallel to the viewing directions in case of elongated luminaires. The brightness of the room ceiling is significantly determined by reflections off the floor and the furniture, which need to feature elevated reflectance.

Indirect lighting (see figure). The luminaires’ luminous flux is reflected into the room and onto the visual task via the ceiling and walls. Its effectiveness is significantly influenced by the reflective properties of these surfaces. Excessive luminance levels on ceiling and walls should be avoided, just as highly diffuse, monotone lighting which lacks shadow effects.

Direct-indirect lighting (see figure). The luminaires’ luminous flux is directed onto the visual task directly as well as indirectly via reflections. This type of lighting permits greater flexibility in terms of spatial arrangement of workstations than direct lighting does. Additionally, this type of lighting creates an improved ratio of directed and diffuse light and thus a balanced luminance distribution as well as more pleasant shadow detail and usually leads to improved acceptance compared to direct or indirect lighting. If this type of lighting is implemented as general lighting, an indirect luminous flux component of ca. 35% of the total luminaire luminous flux has proven to be photometrically and economically advantageous. Direct-indirect lighting is predestined for dynamic light, for examples see chapter "Lighting quality criteria".

(a) direct

(b) indirect

(c) direct-indirect

Figure 3.97: Office lighting types