Lighting planning today can choose from a wide variety of light sources and therefore instruments that enable lighting adapted to people‘s needs. The first approaches towards qualitative lighting planning were made as early as the nineteen fifties. The pioneer in the field of new lighting philosophy was Richard Kelly. His systematisation of light effects today still finds praise.
Richard Kelly managed to free himself from the requirement of uniform illuminance, seen until then as a central criterion of lighting planning. He substituted the question of light quantity with the question of the quality of light. He searched for criteria that differentiated between the perceptional priorities of the viewer. From this consideration a systematisation was created within which Kelly differentiated between three fundamental functions of lighting.
Light for seeing approximately corresponds to the usual quantitative expectation of light. General lighting is created that is sufficient for the perception of the defined viewing tasks. This might be the perception of objects or building structures, orientation in an environment or orientation while moving forwards. But in contrast to quantitative lighting planning, light for viewing is not the aim but rather the basis for extended lighting planning.
Light for viewing according to Kelly‘s theory extends beyond general lighting and accommodates the requirements of people in their surroundings. This type of lighting sets priorities for human perception: firstly objects are recognised that are illuminated in the room the brightest, and then the viewer completes this with perception of the darker objects. In contrast to uniform lighting, light for viewing structures the visual environment into bright and dark zones. It can be quickly and unequivocally differentiated and comprehended. The viewer‘s gaze can be directed onto single objects or zones in the room. This principle not only aids orientation in rooms, it can also be used for the presentation of goods and objects with an aesthetic appeal.
Light for viewing not only illuminates objects or communicates information, but is itself the object of perception. In this respect the light contributes to the aesthetic effect of the room and creates ambience and atmosphere. Light for viewing can be created by candlelight or a light object. The brilliance of the light itself can also become visible via the illumination of specific materials.
To be able to implement these three basic functions of lighting into lighting planning, the industry offers a wide range of lamps that equip various forms of luminaire housings. The design of luminaires does not only have an aesthetic function, but is also influenced by the light guiding optics that in their turn ensure precise light control and glare elimination. Thus equipped, the lighting planner can then work qualitatively with light.
General lighting, supplying light for seeing, can be implemented with direct, wide distribution luminaires for fluorescent or compact fluorescent lamps. These light sources create diffuse light.
Homogeneous light can also be achieved via indirect lighting. But because purely direct or purely indirect light cannot create optimal visual conditions, luminaires with direct-indirect distribution have proven to be highly suitable for general lighting.
For improving general room impressions, illumination of vertical surfaces is recommended. This can be achieved with rectangular or circular luminaires, and with asymmetric reflectors and compact or linear fluorescent lamps.
For improving the general lighting of vertical surfaces, directed light can also be implemented that structures the rooms uniformly and therefore also provides light for viewing.
If light for viewing is ensured, a room impression can be emphasised with light for looking at. This in turn gives a significantly more sophisticated quality of light, and primarily improves rendering of the plasticity and surface structures of illuminated objects. Directed light enables differentiated concentration of light and opens the way for more flexibility with the arrangements of luminaires in the room. An interplay of light and shadow is created that determines the succession of perception.
Room depth also becomes experienceable. Surface-mounted spots with reflector lamps are often used for such tasks. Recessed pan-and-tilt luminaires, usually equipped with high pressure discharge lamps and wide distribution reflectors, can also provide directed light.
In order to emphasise light for viewing it makes sense to keep the general lighting level low. Modelling effects can then be implemented with supplementary directed light. If general lighting is too high, the planner is forced to work with higher wattages for the adjustable light sources. Often the stray light from accentuated areas is sufficient for ambient lighting.
Light for looking at has greater demands on lamps and luminaires than the light for viewing tasks. This mostly means working with almost point-like light sources. As soon as the light from such lamps falls onto materials having glossy surfaces, light reflections are created that are perceived as being brilliant. When light sources themselves become objects, fibre optics, LED and also halogen pin-base lamps can be used. The luminance level of the lamps is experienced as radiant light. Light guidance and the lighting itself is no longer of primary significance.
Bibliography:
History of Light and Lighting - Correspondence Course Lighting
Application/ Vol. 2