Spatial distribution of light
An important criterion of lighting quality is the way in which the light is spatially is distributed, as this determines the pattern of illuminances that will be created. The illuminance recommendations applicable to indoor lighting can be implemented in a number of ways. The light sources can be spread fairly evenly using a system of so-called general lighting (as in a heavy-industry environment) (Fig 6); it can be concentrated in certain areas using localized lighting (as in a hotel room) (Fig 7); or it can be distributed throughout the space but with local accent where needed using a combination of the two systems just mentioned (as in shops).
Fig 6: This site relies entirely on high-quality ‘general’ lighting.
Fig 7: Example of a hotel room that is exclusively illuminated by ‘local’ lighting.
Directional lighting produces high contrasts and modeling effect. It casts deep shadows and creates bright highlights to clearly and dramatically reveal the contours of the object illuminated. However, very deep shadows are unpleasant and can obscure object detail. Good three-dimensional viewing generally calls for directional lighting from at least two directions. A balance in intensity of 1:2 is very often used, as for example in decorative floodlighting installations where the main beam (key light) is backed up by a secondary beam (fill light).
Backlighting and uplighting
In other applications (like display lighting),light from other directions can be added. Backlighting is also employed in decorative lighting to achieve silhouette effects against a bright background. Very dramatic effects can be achieved using lighting from below or ‘uplighting’, which is why this technique is popular in the theatre.
In the case of diffuse lighting, the shadows are soft and the modeling effect is far less pronounced. The impression of a space with completely diffuse lighting is monotonous and it is difficult to identify objects and judge distances. Examples can also be seen in the light distribution of luminaires type.