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The Lighting Design Objectives (LiDOs) procedure

30 Jun 2019

The Lighting Design Objectives (LiDOs) Procedure. The procedure guides the practitioner from having specified lighting design objectives (LiDOs) that relate to how illumination quantity and distribution may influence the appearance of a lit space, to developing a specification of a direct flux distribution (DFD) that would achieve the required balance of LiDOs. Throughout the process, the practitioner may give priority to achieving illumination efficiency or creating an illumination hierarchy.

Above:  The Lighting Design Objectives (LiDOs) Procedure. The procedure guides the practitioner from having specified lighting design objectives (LiDOs) that relate to how illumination quantity and distribution may influence the appearance of a lit space, to developing a specification of a direct flux distribution (DFD) that would achieve the required balance of LiDOs. Throughout the process, the practitioner may give priority to achieving illumination efficiency or creating an illumination hierarchy.

 

Abstract

This procedure is based on the concept that there is real advantage to be gained from changing the illumination metrics used for specifying, measuring and predicting lighting applications so that they relate to peoples' responses to visible effects of lighting in indoor applications. The currently used illumination metrics are directed towards providing for visibility, or more specifically, enabling people to perform visual tasks efficiently and accurately. Proposals are made for lighting metrics that relate to how the quantity and distribution of illumination may influence the appearance of peoples' surroundings, and while the procedure includes work environments, it encompasses all types of indoor activities and locations. The procedure enables lighting design objectives (LiDOs) that relate to peoples' responses to visible effects of lighting upon their surroundings to be specified quantitively, and this leads to the development of a technical specification of lighting installation performance that enables the selection of luminaires to provide the illumination quantity and distribution that will achieve the LiDOs. The implications for both general lighting practice and professional lighting design are discussed.

The practice of lighting

Lighting practitioners are poorly served by the illumination metrics that are currently used to specify, measure and predict lighting in buildings. Almost a century has passed since the Lumen Method   was introduced, providing a simple tool for enabling a prescribed average illuminance to be provided over the horizontal working plane (HWP). What is truly remarkable is that, to this day, the concepts upon which it is based persist as the basis for specifying illumination levels in lighting standards.                   

Probably the world's most often referenced indoor lighting standard is the European Standard EN 12464-1 Indoor Work Places, which defines the purpose of lighting as "to enable people to perform visual tasks efficiently and accurately", for which the prime criterion is "a maintained illuminance over the task area on the reference surface, which may be horizontal, vertical of inclined" and "the task area shall be illuminated as uniformly as possible." This definition requires the designer to specify a reference plane for each task area. However, the schedule of activities for which maintained illuminance values are specified in this "work place" standard includes locations such as restaurants, hotels, theatres, concert halls, cinemas and so forth, making the notion of identifying a visual task to be performed efficiently and accurately quite meaningless and giving users little option but to fall back on the default position of a HWP that needs to be uniformly illuminated to the specified level. As an example of the dominant role that HWP has within lighting practice, ‘a 400 lux installation' is universally recognised as one that provides that average illuminance over the HWP with acceptable wall-to-wall uniformity, irrespective of whether the human activity associated with the space is in any way work-related.

The mid-years of the last century saw the emergence of architectural lighting design as a professional practice with objectives that reject virtually everything that lighting standards such as EN 12464-1 aim to achieve, including the use of illumination metrics to specify lighting objectives. Since then lighting design software has been developed that enables designers not only to visualise onscreen how lighting may affect the appearance of a chosen architectural space, but more generally, how it influences the appearance of peoples' surroundings. The lighting profession is now divided between practitioners who use illumination metrics to achieve reliable and efficient compliance with lighting standards, and those who apply lighting to influence the appearance of peoples' surroundings and who shun the use of illumination metrics which they see as inhibiting their creativity and their scope to ‘think outside the box'.

It is proposed that there is scope for an innovative procedure that combines components from both sides of this division. Lighting's role in influencing the appearance of peoples' surroundings provides a sensible basis for determining the overall illumination quantity to be provided, where ‘surroundings' is taken to include all visible surfaces and objects within the space. Within the space, the appearance of details, which may include anything that deserves attention (including visual tasks) may be crucially affected by illumination distribution, and managing illumination quantity and distribution within an enclosed space calls for competent application of illumination metrics. Application of such a procedure should support the achievement of any set of lighting design objectives without inhibiting innovative design options, as does imposition of the uniformity criterion.

 

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