Sunday 15 May 2011

The standards and recommendations that guide general lighting practice bear no sensible relationship to providing for human satisfaction. The conventional way of specifying indoor lighting levels in terms of workplane illuminance is defended as the means for ensuring appropriate levels of visual performance, but this claim has been challenged and shown to be unsupportable. Meanwhile, current lighting standards drive general practice towards installations which direct high proportions of the lamp lumens downwards onto the horizontal workplane, thereby dictating the lighting distribution that has to be provided to satisfy energy efficiency standards and sustainability ratings. Without a valid measure of how lighting provides for user satisfaction there can be no valid measure of lighting efficiency. The unavoidable conclusion is that lighting standards are in need of fundamental revision.

It is argued that the prime factor determining how much light needs to be provided for a given category of indoor space is meeting peoples’ expectations for that space to appear adequately illuminated. On this simple basis, an entirely new lighting criterion is required to replace visual performance. The concept of perceived adequacy of illumination (PAI) is proposed as the basis for specifying illumination levels in general lighting practice, and this calls for a lighting metric that corresponds to visual assessments of the ambient level of reflected light arriving at the eye from surrounding room surfaces. Mean room surface exitance (MRSE), being the average luminous flux density (lm/m2) from surrounding room surfaces, is such a metric. Its adoption would recognize that direct light at the eye from luminaires and fenestration comprises glare, and this component of illumination detracts from, rather than adding to, assessment of illumination adequacy. It should be excluded from illumination measurements concerned with assessments of adequacy.

Adoption of a PAI-related metric for specifying illumination quantity in general lighting practice would lead to a fundamentally new understanding of how light is to be distributed within indoor spaces. It would be recognized that the role of luminaires is primarily to control the initial light distribution, after which interreflection between the room surfaces generates the light distribution presented to the eye. Room surfaces would be seen to be integral components of the lighting system, as influential as lamps and luminaires. This new understanding would have profound implications for lighting designers. Instead of being coerced into applying “efficient” downlighting distributions in order to comply with sustainability targets, they would have freedom to devise lighting distributions that interact with room surfaces and objects of interest, creating visual hierarchies and removing conflicting aims that currently differentiate lighting design and illumination engineering objectives. New lighting standards based on PAI may be seen as the means for changing everything from lighting education through to luminaire and fenestration controls, but before such standards can be prescribed some good human factors research is needed.

For more background on this topic, refer to:
Cuttle C. Towards the Third Stage of the Lighting Profession. Lighting Research & Technology, 2010; 42(1): 73-93.

Section 2.1, Ambient Illumination, from Cuttle, Christopher. Lighting by Design, Second edition. Oxford, Architectural Press, 2008.

See also:
Discussion in SLL Newsletter, three issues for Nov/Dec 2009 to March/April 2010 (Vol 2(6) to 3(2)). Note: SLL is the Society of Light & Lighting, London.

Guest Editorial, LIGHTING: Art and Science for International Lighting Designers, Oct/Nov 2009; 29(5): 14-16. Note: LIGHTING is the official publication of the Illuminating Engineering Society of Australia and New Zealand.

Cuttle K. Opinion: Lighting Criteria for the Future. Lighting Research & Technology, 2010; 42(3): 270.
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Kit







9 comments:

  1. Kit, I absolutely agree with this approach. Trying to design around ever more restrictive requirements for illuminance levels on notional work planes that are either ill defined or not defined at the time when lighting has to be designed is a frustrating issue. It is even more problematic when the default solution is to provide " task level" lighting across the entire floor plate. This is an unconscionable waste of energy when we are supposed to be reducing energy use!

    Kevan Shaw

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  2. Kit,

    Yet another great paper delivered today at PLDC. The logic of this position is indisputably clear and it is really interesting to see how many other people are talking about Luminance rather than Illuminance as the key to lighting design!

    Kevvan Shaw

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  3. Just met with peter Boyce David Low and Peter Raynham at LuxLive and instigated a spirited discussion on MRSE. There is definitely an acceptance that the way we measure light and the consequent standards do need changed. Somewhat less agreement that MRSE is the solution. I think it seems to simple to them! Unfortunately the greatest ideas are always simple once you get to understand them!

    We do need some more research to convince them and the other doubters!

    Kevan Shaw

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  4. Thanks Kevan, and for anyone who is wondering about the PLDC paper that Kevan refers to in his 21 October comment, I presented it on that day at the Professional Lighting Design Convention held in Madrid. The title is "Perceived Adequacy of Illumination: A new basis for lighting practice", and it is published in the convention proceedings.

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  5. Kit, would it be possible to share the paper from PLDC Madrid or can I find it somewhere. I believe we have it in a magazine somewhere in the office, but can of course not find it when I need it...

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  6. Thanks Kit, I enjoyed reading this post! My interest has really only just intensified from, I would say a fairly'casual'perspective so useful I think to engage at what looks to be a crest of change perhaps? btw we have actually met and chatted briefly. I attended the "lighting for the future" workshop in Wellington last April. You started something! You'll be one of the first I read when I get re-settled (I re-located to Brisbane recently!) Warm regards, Kevin Webby.

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  7. Kit, I find the division to be engineers vs designers and a colossal waste of time in such a small profession. It takes both types and we should work together without feeling superior to the together group. It may interest you to know that the "pre Richard Kelly" LD's at the Worlds Fairs were usually GE electrical engineers who could also design artistically. One of these Walter D'arcy Ryan co founded the IES and headed the Electrical Department at GE in Schenectady. He lit Niagara Falls (in color) in 1906, the Hudson Fulton Celebration in 1909, the Panama Pacific International Exposition in 1915. There are many more, he ended his life by "fixing" the lighting at the 1933 Chicago. The "Rainbow Scintillator" in 1915 was a battery of 48-36" inch searchlights (which he was perfecting for Navy ships at the same time) was spectacular and very beautiful. I wrote an article about him in 11-2000 issue of LD&A if you would like more information.

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  8. The Illuminating Engineering Society of North America (IESNA) defines light as
    “radiant energy that is capable of exciting the retina and producing a visual sensation.”
    Light, therefore, cannot be separately described in terms of radiant energy or of visual
    sensation but is a combination of the two.

    I think Jill makes a valid point in relation to working together as I know from a furniture design perspective that manufacturing support for instance can be a highly desirable collaboration although I feel as if this is one thread of what Kit is attempting to unravel here? Eg. Engineers are great with the science no doubt and I think designers are good when it comes to interpreting objects & environmental concepts and 'creating' the visual hierarchies so to some extent it makes sense for these people to contribute in their areas of strength. I acknowledge the cross-pollination of knowledge between disciplines! I'm not sure who sets the guidelines for general lighting practice but the one factor that hasn't been commented on here subsequently is the human one! General practice, to me implies something about the consumer (and for the purpose of this conversation I mean public/commercial excluding domestic) so you could have the most brilliantly engineered/designed lamp or luminaire in the world but if consumers are working toward parameters different to those prescribed by engineers and or designers then probably no-ones expectations will be met including the end-user which I thought would be the ultimate target for human satisfaction? The unfortunate paradox to this is that in my museum/art gallery sector experience the punter doesn't necessarily know what to expect. The most common feedback I received was "to dark" which is fair enough or "well lit" which I never knew quite how to take? I for one would appreciate the metric, the meaningful general practice guidelines backed by science and delivering an appropriate human experience.

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  9. Thank you, Kit! What I love about your "reformation" is that it would pave the way for architectural lighting designers to be a part of creating lighting standards. Because our practice is based more directly with the human element of lighting, our input would necessarily improve end-results, as humans are ALWAYS the ultimate goal.

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