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Cuttle's plea to a divided lighting profession

15 August 2012 15.30 BST

(New Zealand) - Lighting expert Christopher ‘Kit’ Cuttle calls for 'best practice' and 'architectural' lighting designers to work together for the good of the profession.

We have a divided profession. The first illuminating engineering societies, formed more than 100 years ago, set the initial agenda for professional involvement in lighting. The purpose for providing Illumination was seen to be to satisfy human need for visibility, and the aim was to optimise illumination provision for efficiency and economy through application of science-based principles. This approach is entirely logical and has been adopted in many countries throughout the world, where the members of national IES or equivalent societies have been strongly influential in establishing lighting standards. However, around the middle of the 20th century it became apparent that there was growing dissatisfaction with this agenda as it failed to include the professional activities of a newer breed of lighting designers, and this has led to the emergence of the IALD in the North America, and in Europe, of ELDA, now superseded by the PLDA. Defining the purpose for providing illumination as seen by these groups is less straightforward, but one thing would seem to be unarguable: rather than thinking of illumination as the medium that makes things visible, these designers see lighting principally in terms of how it influences the appearance of peoples’ surroundings. This difference of visibility and appearance being envisioned as the purpose of lighting underlies the professional division that remains with us to this day.

Visibility as the purpose of lighting
Rather than employing a scale of task visibility, lighting standards make reference to relative visual performance (RVP) to specify illumination levels appropriate for various activities. The validity of RVP has been demonstrated many times for critical viewing situations, such as nighttime illumination of roadway signs, but its application to indoor general lighting practice lacks rigour. Visual performance research has been based almost exclusively on subjects viewing two-dimensional, diffusely-reflecting reading tasks, and researchers have chosen this viewing situation as it enables visual performance to be expressed as a function of illuminance. This has led to the widespread misunderstanding that prescribed levels of visual performance for all manner of activities can be assured by specifying task illuminance values. For example, in 2008 the IES of North America published Guide to Designing Quality Lighting for People and Buildings, which states that “The foundation for lighting design is ensuring that people have enough light to safely, efficiently and accurately perform predominant visual tasks.” From this statement it may be inferred that “enough light” is all that is required to ensure a prescribed level of RVP for a given activity, but the reality is far more complicated. This because the two-dimensional diffusely-reflecting task is a special case, whereas the general case includes visual tasks that may be three-dimensional and have quite different optical characteristics, so that predicting visibility has to take account of the form, texture, gloss, colour contrast, and perhaps, the transparency or translucency of the task materials.

Application of RVP in everyday situations would require definition of both the eye-task geometry and the luminance distribution of the entire surrounding light field. To specify a lighting condition for a real visual task that will ensure satisfaction of a prescribed visual performance criterion is no mean undertaking, and for this reason, it is very seldom done outside a research laboratory.

If such measurements were to be conducted in actual workplaces, those who claim that the currently recommended (or sometimes mandated) illuminance levels must be provided to maintain workers’ productivity and health would find themselves confronted by some challenging data. Figure 1 shows that, for the typical reading task of 12-pt type on white paper, it requires just 20 lux to provide for the relative visual performance criterion of RVP=0.98, this value being generally accepted as the highest practical RVP level for lighting applications. It can be seen that for the required illuminance to exceed 100 lux, the font size would have to be reduced to 6-pt, or alternatively, reduced to 10-pt but printed onto dark-coloured paper, which has the double effect of reducing the background luminance and the task contrast. However, even this value of 100 lux falls far short of the levels conventionally provided for applications where reading tasks are prevalent, which typically fall within the range 300 to 500 lux, and it is clear that such levels can be justified on the basis of visual performance only by presuming that either the users are partially visually defective, or that they are persistently required to cope with visual tasks equivalent to reading very small print with very low contrast on low reflectance backgrounds. It can be seen that for everyday reading tasks recommended illuminance values are far out of step with visual performance requirements. If we transfer our attention to real tasks involving complexities such as three-dimensional form, texture and gloss, the situation would be further confused and greater discrepancies could be expected. It needs to be recognised that the often-made claim that the illuminance schedules are research-based and must be enforced to maintain productivity levels is false.

Appearance as the purpose of lighting
While the first illuminating engineering society had been founded in 1906 in New York, it was also in that part of the world that the first clear signs of an alternative faction emerged. In the years following World War II, leading architects were turning to a new breed of lighting professionals. Often these were individuals who had acquired their skills as stage lighting designers and who found themselves able to establish close rapport with architects. The pioneers of this development are now legends; designers such as Richard Kelly, Abe Feder, and Stanley McCandless in the USA, and J.M. Waldram in the UK; and architects who sought to arouse emotional responses in people entering their buildings found that they were able to communicate readily with these designers.

They responded to the architects’ expectations and had the ability to bring the magic of theatrical experiences into their creations. It was a symbiosis, and it is important to recognize that it was not that these designers raised the standard or quality of lighting design: they redefined its purpose.

In 1952, Richard Kelly set out his design philosophy in a lecture delivered at a joint meeting of The American Institute of Architects, the Society of Industrial Designers, and the Illuminating Engineering Society, in Cleveland, Ohio1. He identified “three elemental kinds of light effect”; these he described as: ambient luminescence, focal glow, and a play of brilliants. If any words could be said to have initiated the emergence of lighting design as a profession distinct from illumination engineering, it surely has to be these. Up to his death in 1977, Kelly developed close, almost intimate, working relationships with several of the leading architects of the era and was acknowledged to have made significant contributions to a number of major architectural projects.

It may be asked to what extent can the balance of these three kinds of light effect be applied for describing current lighting practice? Contemporary photographs of Kelly’s work mostly comprise rather grainy half tones, so I have reviewed my own collection of photographs for examples which, I think, characterize dominance of each of the effects, even though Kelly had no connection with any of them. They appear as Figures 2 to 4.

Since that time there has been an uneasy relationship between lighting designers who see themselves to be involved in the process of architectural design, and those who design lighting installations to comply with all current standards and recommendations for best practice. For the remainder of this paper we will refer to these two types of lighting practitioner as ‘architectural’ designers and ‘best practice’ designers. No pejorative is intended by these terms: they are proposed only to describe two legitimate approaches to designing lighting installations. Of course there are other individuals who plan lighting installations without ever rising to the standards of either of these categories, but that is another issue.  It might seem that the difference between these two designer groups is irreconcilable, but the aim of this paper is to suggest an alternative outcome.

‘Architectural’ lighting designers and ‘best practice’ lighting designers
When we look at attitudes towards lighting standards, which are taken here to include the whole range of codes and recommended practice documents, the differences between these two types of practitioner become starkly apparent. The ‘architectural’ designers find it quite absurd that illuminance uniformity should be cited as a measure of lighting quality, and that in order to satisfy demands for energy efficiency they should be required to focus light output onto the horizontal workplane. Howard Brandston, who started in lighting as Stanley McCandless’s assistant, has produced his own rule, “Rules are a substitute for thinking”, to which he has added, “Codes and standards can distract us from lighting practice.”2 Such designers resent the very existence of lighting standards. Meanwhile, the ‘best practice’ designers depend on lighting standards in order to do their job. It is their role in life to devise installations that are fully-compliant and which thereby represent the best of current lighting practice. For the past few decades, illuminance schedules have been maintained at their current levels, which could be described as saturation levels, and standards have responded by increasing their scope to include additional rules relating to other aspects of lighting. These range from ‘lighting quality’ factors, such as glare control, to others concerned with health, safety and sustainability. This added complexity has had the effect of raising the authority and self-assurance of ‘best practice’ designers.

We need a total change of attitude towards standards. ‘Best practice’ designers need to come to terms with the fact that the illuminance schedules that form basis of lighting standards have escalated way beyond levels that can be justified on the basis of visibility, and new thinking is needed on what is meant by “enough light”. ‘Architectural’ designers need to recognise that lighting standards are not going to go away, and for there to be standards that specify “enough light” in ways that achieve that objective but do not “distract [them] from lighting practice”, they will need to become involved in the process of making standards. This could lead to a shared purpose for all 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 physical environments to create various types of visual experience. In his words, “Focal glow draws attention, pulls together diverse parts, sells merchandise, separates the important 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 distracting 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 shadowless 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 usually 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 that 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 conversely, 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 surrounding environment, or in other words, the density of light that the space (not the light sources) makes available at the eye. Procedures for calculation and measurement have been explained, and the proposal being advanced here is that the workplane illuminance schedules in the current standards be replaced with schedules of MRSE, specified in lumens per square metre. The difference 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 generally be lower than the current illuminance schedule values because they exclude direct 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 identify the things that are visually important and to apply direct light to achieve appropriate 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 properties 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 important objects are invariably to be found uniformly arrayed on the horizontal workplane 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 reevaluation of some familiar lighting techniques. Indirect lighting, or uplighting, and wall washing have long been recognized as attractive ways of lighting non-working spaces, but far too inefficient general use. Whether designing for compliance with MRSE specifications or for meeting expectations for a pleasantly lit space, these lighting distributions would be found to be visually effective and capable of achieving high efficiency where the distribution of direct light has been sensibly related to the room proportions and surface reflectances. 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 contemplate 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’ designers 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.

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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.

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 matter 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 Illumination: a new basis for lighting practice. Proceedings of the 3rd PLDC Professional Lighting Design Convention, Madrid, 2011. 81-83.


Figure 1: The task illuminance required to provide for relative visual performance RVP = 0.98 for a range of reading tasks. The reader is a normal-sighted 25 year-old with a viewing distance of 350mm. The reading matter is black print, ranging from 6- to 14-point size, on three types of paper: light (reflectance p=0.9); medium (p=0.6); and dark (p=0.3).

Figure 2: ‘Focal glow’ dominant. This photograph is offered as an example of the first of Richard Kelly’s “three elemental kinds of light effect”. Grand Union Station, Washington DC, USA. Lighting design: William M.C. Lam.
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