LIGHTING DESIGN INTENT & CRITERIA -...

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Ball State Architecture | ENVIRONMENTAL SYSTEMS 2 | Grondzik 1

LIGHTING DESIGN INTENT & CRITERIA


Lighting Design Intent

1. A clear design intent should be evident in all elements of the visual field.

William Lam:Perception and Lighting as Formgivers for Architecture

from … “Some rules of thumb for good design”

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Design Process Flow

• Design intent• Design criteria• System ideas/proposals—initial• Design methods (patterns, tools, …)• System ideas/proposals—refined• Implementation methods (physical things)• System ideas/proposals—near final• Design validation

– During design (internal quality control and commissioning)– During construction (internal quality control and

commissioning)– During usage (via complaints or via POE)

gene

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Lighting Design ProcessStart (“problem”)

Stuff happens

End (“solution”)

Design intentDesign criteria

*Designconcepts

*Designvalidation Lighting design methods*

* to be discussed more over the next weeks

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Issues > Intent > CriteriaISSUES

Intent

Criteria

Flow intodesign process


Design Intent

Examples:– The lighting will be energy efficient– Daylighting will be utilized (is this truly intent or simply

a method?)– The lighting will be reasonably comfortable– The lighting will increase sales– The lighting will increase productivity– The lighting will enhance wayfinding– The lighting will contribute credits for LEED– The lighting will win a design award

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Design CriteriaExamples:

– The lighting will be energy efficient [intent]• Perhaps: will meet the requirements of ASHRAE Standard 90.1• Perhaps: will be 30% more efficient than ASHRAE 90.1

– Daylighting will be utilized [intent] (confirm not just a method)• All spaces will have a minimum daylight factor of 2%• Daylighting will reduce annual electric lighting energy

requirements by 60%– The lighting will be reasonably comfortable [intent]

• 80% of occupants will rate the lighting as very comfortable– The lighting will be aesthetically pleasing [intent]

• Appearance will match three selected precedents


Design Criteria

More examples:– The lighting will increase sales [intent]

• The lighting will increase sales by 20% compared to sales in existing stores

– The lighting will increase productivity [intent]

• The lighting will increase worker productivity by 10% compared to the productivity in existing offices

– The lighting will support wayfinding [intent]• 25% fewer requests for assistance in finding

major functional spaces will be made at the

note that criteria can be quantitative (useful during design—and amenable tocalculations) and/or qualitative (typically amenable to judgment and POEs)

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Methods

Methods should never be put forward as intent or criteria (with a few exceptions)

– Fluorescent lamps are NOT an intent– Fluorescent lamps are NOT a criterion– Fluorescent lamps are a method (a means,

not an end; a cause, not an effect)– More on lighting design methods later

a method, such as daylighting, may become an intent if it is so strongly “held”as to be non-negotiable (even then, good daylighting is likely the real intent)


A Reminder

A proposed design solution is a hypothesis …– The designer believes that IF I do this, such and

such will THEN result– A hypothesis is a prediction, a prognosis, a wish,

a wild guess (depending upon experience and extent of project research)

– A hypothesis is NOT a fact– Hypotheses must be tested and verified– Thus, design moves must be verified (they will

have consequences—see image on first slide)

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Design ValidationValidation of design moves during design is essential, otherwise it will be too late for the victims of a bad decision (the “decision” will have been built and occupied by real people)

– Many lighting design validation tools are available• Precedents (case studies) • General rules and patterns• Hand calculations• Computer simulations• Physical models (difficulty in scaling electric light sources

limits this tool … this was not the case with daylighting)• Full scale mock-ups (cost may limit this tool)


Implementation Methods

These are the objects and systems that can produce the desired effects in a completed building

– Implementation methods convert concepts into physical reality

• Clerestory apertures• Indirect lighting fixtures• Digital lighting controls• Reflective wall surfaces • … and so on

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Lighting Design IssuesQuantitative issues

– Illuminance– Luminance– Energy performance– Environmental performance– First cost– Life-cycle costs– ….

issues become intent by assigning value/direction; and thence become criteria by assigning minimum acceptable performance benchmarks


Lighting Design Issues

Qualitative issues– Glare– Brightness (and brightness patterns)– Color rendering– Aesthetics– Appropriateness– ….

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Design Issues qualitative

space type

quantitative

source:


Some Context for Lighting DesignThere is no unified theory of visual comfort(as there is with thermal comfort)—there is

no “visual comfort zone” diagram … no adviceregarding how a bit less glare might trade off

with a bit less illuminance or how color rendering might trade off with luminance. The lighting design process

essentially involves addressing each issue of concern in sequence … with conceptual coordination by the

designer left to deal with the disaggregated nature of the process.

We’ll look at the issues of illuminance and glarein some detail in the following slides as these are usually

important concerns for most projects

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Illuminance*On horizontal surfaces

– Requirements are generally a function of the visual acuity required or expected for a task

– The purpose of illuminance is to provide adequate light for successful task completion

– Task is the key (the designer is usually addressing a defined visual task versus general space-rendering)

– Task location(s) are of concern– Multiple tasks require providing for the “worst” task, or

for flexibility over time … or for flexibility over space– Measured in lux (SI) or fc (footcandles, I-P)

*the density of light falling on a surface; the human eye cannot detectilluminance, but can detect its result (brightness/luminance)


Illuminance

On vertical surfaces– If there is a vertical task (pinup, bulletin board,

artwork, signage, …), then design concerns are the same as with horizontal illuminance

– Without a defined task, vertical illuminance requirements are generally a function of spatial design intent

• To illuminate walls (to avoid the “cave” effect)• To draw attention, provide focus• To reduce contrast• To … support aesthetic design intents

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Visual Acuity FactorsIlluminance recommendations are generally based upon visual acuity—the ability to see detail; this ability is affected by:

Size of detail• Typically there is only minor architectural control over this factor via

establishment of viewing distances or through signage design; the architect has little or no control for most “work” tasks

Luminance of detail• A result of illuminance and reflectance; illuminance is fully within

the realm of lighting system design, while reflectance is often a property of a non-architectural object (such as the page of a book)

Contrast at detail• A result of task-background luminance relationships and glare

condition; these factors are partially in the realm of lighting design and partially a property of the task


Visual Acuity Factors

• Size

E E E E E E

• Luminance

E E B F

• ContrastEEEEE

easier to see detail more difficult

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DesignIlluminances

illuminance categories

from the IESNALighting Handbook (9th

edition)—which is a guideline (not a code or standard)


Illuminance Adjustments

The 8th edition of the IESNA Lighting Handbooksuggested increasing illuminance by 1 “category”

for each clear instance of a mitigating factor(poor eye condition, poor contrast, high speedtask) … the current edition (9th) is less specific

regarding such adjustments—but the idea of adjustments is still valid (and recommended).

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Glare

A negative visual sensation resulting fromexcessive brightness or excessive contrastin the field of view. Glare can be categorized by:

– Degree of impact: blinding, disability, discomfort– Source/receiver relationship: direct or reflected


Glare: Degree of Impact

Blinding glare: vision is temporarily disrupted (zero visual acuity for some period of time)

– Example: oncoming car headlights at night (a result of excessive contrast)

– Example: looking at the sun through a window (a result of absolute brightness)

– Source may be direct or reflected (although most commonly it is direct)

– Blinding glare should never be encountered in a building (but occasionally it is)

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Glare: Degree of ImpactDisability glare: visual acuity is reduced; the viewer is physically less able to effectively complete visual tasks

– Example: a reflected image of a light fixture seen in a computer screen (a reflected glare situation, often called a veiling reflection)

– Example: looking at a TV that is located in front of a window (a direct glare situation, due to excessive contrast)

– Source may be direct or reflected (either is likely) and the negative effect is often a result of contrast versus absolute brightness

– Disability glare is undesirable in a building, but budget constraints may make total elimination difficult


Glare: Degree of ImpactDiscomfort glare: visual acuity is not measurably reduced, but glare has intruded into the viewer’s consciousness; a viewer may be psychologically less able to complete visual tasks

– Example: reflection of ambient light from a computer screen (no image is seen, just reduced contrast)

– Example: marginal brightness ratios in a room– Source may be direct or reflected and the effect is

usually a result of contrast versus absolute brightness; the key issue may be attention-diversion

– Discomfort glare is undesirable in a building, but is very difficult to totally eliminate (due to budget and the qualitative nature of problem)

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Glare: Source

Direct glare: a too-bright object or too-great a contrast scene is in the line of sight of an observer (no intervening “transmitter” is involved)

– This should be readily predictable during design, and thus readily solvable … simply:

• Ask yourself what’s going to be too bright (more technically, too luminous)

• Then, reduce brightness (luminance) or block view to object


Glare: SourceReflected glare: a too-bright object (the most common situation) or too-great-a-contrast scene (less common) is brought into the line of sight of an observer by the intervention of a reflectivesurface

– This combination of factors is not necessarily obvious during design, thus some brainstorming is needed

• Ask yourself what’s going to be too bright• Ask yourself what’s likely to be reflective• Then, consider the possible geometries between the above

elements and users of the space and take appropriate action

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Glare SummaryGlare

– Is a perception, not an “object” or a “flow”– Requires a human receptor/evaluator

• There is no glare in an unoccupied room • Perceptions may vary from person to person• Design to mitigate glare often relies upon patterns or

statistics

– Glare cannot be “admitted through a window”(light can be admitted)

– Glare cannot be measured by equipment (luminance can be measured)


Glare ?

Do you know this person?

Do you see the person with the knife?

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Glare ?

nice lamp shade nice pickup truck


Glare ?

what street? what data?

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Another Visual Phenomenon

Sparkle– A positive visual sensation resulting from

excessive brightness or excessive contrast (in the field of view)

– Fireworks, a chandelier, a diamond, …– Sparkle can be introduced to a space (in

moderation)


Sparkle?

someone thought so

“ball four”(just a little bit off the plate)

sparkle or glare?

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