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128 TECHNOLOGY / DEBATE lighting designers.


A SHARED PURPOSE Look again at Kelly’s description of three kinds of light effect. He was not describing the lighting installation, or the appearance of the lit scene, but rather the potential of the illumination (whether daylight or electric lighting) to interact with physi- cal environments to create various types of visual experience. In his words, “Focal glow draws attention, pulls together diverse parts, sells merchandise, separates the im- portant from the unimportant, helps people to see.” (See Figure 2) This says everything about visibility that the ‘best practice’ designers could have been saying if they had not been sidelined by the simplistic notion of workplane illuminance. Kelly again, “Play of brilliants excites the optic nerves, and in turn stimulates the body and spirit, quickens the appetite, awakens curiosity, sharpens the wit. It is distract- ing or entertaining.” (See Figure 4) Now we are into a region of lighting design where only ‘architectural’ designers should dare to tread. The last sentence is profound. While the ‘best practice’ designers aim to eliminate distraction (which they classify as glare), the ‘architectural’ designers seek to entertain with brilliants. The other one of Kelly’s three kinds of light is quite different in nature. Of this he says, “Ambient luminescence produces shadow- less illumination. It minimizes form and bulk. It minimizes the importance of all things and people. It suggests the freedom of space and can suggest infinity. It is usu- ally reassuring. It quiets the nerves and is restful.” (See Figure 3) He adds that “Visual beauty is perceived by an interplay of all three kinds of light, though one is usually dominant.” This brings us to the central proposal of this paper. Where Kelly would have described ambient luminescence to be dominant, this would be a situation where the illumination at the eye would be due mainly to diffusely reflected light from the surrounding environment. A high level of this ambient illumination within the volume of the space would correspond with the perception of a brightly lit space, and con- versely, a low level with a dimly lit one. It is proposed here that this concept provides a sensible basis for illumination standards.


A NEW CRITERION FOR INDOOR LIGHTING Recently the author has proposed perceived adequacy of illumination as the criterion on which indoor lighting standards should be based, leading to illumination schedules being specified in terms of a metric that relates to peoples’ assessments of whether


or not a space appears to be adequately illuminated.3,4


Mean room surface exitance


(MRSE) is proposed as such a metric, this being the average level of lumens per square metre reflected from the surround- ing environment, or in other words, the density of light that the space (not the light sources) makes available at the eye. Proce- dures for calculation and measurement have been explained, and the proposal being advanced here is that the workplane illumi- nance schedules in the current standards be replaced with schedules of MRSE, specified in lumens per square metre. The differ- ence is that MRSE includes only light that has undergone at least one reflection, and instead of being a measure of light incident on things to be seen, it refers to reflected light at the eye. The recommended MRSE values will gener- ally be lower than the current illuminance schedule values because they exclude di- rect light from luminaires and windows, but that does not mean that task illuminance values should be correspondingly reduced. It will be up to the lighting designer to iden- tify the things that are visually important and to apply direct light to achieve appro- priate emphasis and visibility. An identified object may be a sheet of printed paper; or a product on an assembly line; or a retail display; or a marble sculpture. Whichever, the direct illuminance should be related to the ambient level, indicated by the MRSE value, according to the emphasis required, and the distribution of direct light should be chosen according to the surface proper- ties of the object. While there would, of course, always be some situations where it would be quite appropriate to direct most of the luminaire outputs onto the horizontal workplane, this would occur as the result of a decision, and not as a matter of course. The nonsense of acting as if all visually im- portant objects are invariably to be found uniformly arrayed on the horizontal work- plane would become too obvious to ignore. Lighting efficiency would be seen to be strongly influenced by the reflectances of room surfaces receiving direct illumination, and this would lead to a complete reevalu- ation of some familiar lighting techniques. Indirect lighting, or uplighting, and wall washing have long been recognised as attractive ways of lighting non-working spaces, but far too inefficient general use. Whether designing for compliance with MRSE specifications or for meeting expec- tations for a pleasantly lit space, these lighting distributions would be found to be visually effective and capable of achiev- ing high efficiency where the distribution of direct light has been sensibly related to


the room proportions and surface reflec- tances. Alternative light distributions for libraries, art rooms, recreation centres, and so on would spring to mind and gradually all lighting designers would settle down to thinking about how light may be distributed within any space to suit the light reflecting surfaces, and how the combination of direct and reflected illumination within the space would affect the appearance of the three- dimensional objects within it. In this way, design thinking would progress quite naturally from ambient luminescence to focal glow, and ahead would lie the play of brilliants. While nobody should contem- plate incorporating these latter two aspects of lighting into standards, the perceived adequacy of illumination criterion does offer a basis for a shared concept of the purpose of lighting. Making it happen would require some changes of attitude. ‘Best practice’ designers would need to accept that the basic criterion for “enough light” has to change, and ‘architectural’ design- ers would need to apply themselves to the process of creating standards. The objective would be lighting standards that specify “enough light” without restricting how direct light is to be distributed. With that common ground, ‘architectural’ and ‘best practice’ lighting designers should find that there is quite a lot that they can learn from each other.


www.kit-lightflow.blogspot.com


Acknowledgments Thanks are expressed to Prof Mark Rea and Dr John Bullough of the Lighting Research Center, Rensselaer Polytechnic Institute, for the RVP program used to produce Figure 1, and to Margaret Maile Petty for providing material on Richard Kelly. Also, thanks for comments on the text to Kevan Shaw, and to past colleagues Peter Boyce, Mark Rea, Joe Lynes and Howard Brandston.


References 1. Kelly, Richard. Lighting as an Integral Part of Architecture. College Art Journal, 12, no.1 (Autumn 1952): 24-30. 2. Brandston, H.M. Learning to See: A mat- ter of light. Illuminating Engineering Society of North America: 2008. 3. Cuttle C. Towards the Third Stage of the Lighting Profession. Lighting Research & Technology, 2010; 42(1):73-93. 4. Cuttle, C. Perceived Adequacy of Illumi- nation: a new basis for lighting practice. Proceedings of the 3rd PLDC Professional Lighting Design Convention, Madrid, 2011. 81-83.


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