Lighting : February 2014 Lighting (v2-HR)
February/March 2014 | LIGHTING MAGAZINE 63 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 explained5, 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. Figure 3. ‘Ambient luminescence’ dominant; the second of Kelly’s kinds of light effect. Samslung Essel, Klosterneuberg, Austria. Architect: Heinz Tessar. 62 LIGHTING MAGAZINE | February/March 2014 ‘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 jobs. 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 recognize 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.1 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.
April May 2013
Lighting April 2014 - Vol 34 Issue 2