electric lighting design analysis tools

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Ball State Architecture | ENVIRONMENTAL SYSTEMS 2 | Grondzik 1

ELECTRIC LIGHTINGDESIGN

ANALYSIS


Reminder: Electric LightingDesign Analysis Tools

• Look-ups: pre-canned solutions provided by product manufacturers to speed adoption of solutions—in graphic or tabular format

• Correlations: product-generic methods—such as the zonal cavity method—applicable to many solutions

• First principles: employing basic physics relationships—such as the point-to-point method

• Computer simulations: to tap the data storage and number crunching capabilities of computers—often coupled with rendering routines

• Analog mock-ups: not common except for proof-of-concept demonstrations

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Illuminances of Concern

• Design illuminance = design criterion– The target or benchmark that defines “success”

• Initial illuminance = the illuminance experienced upon first operating a system (space and equipment are new)– LLF is set to 1.0 to estimate initial illuminance

• Maintained illuminance = the illuminance found in a space after some defined time (perhaps 2, 4, 5 years)– Condition that occurs when LLF assumes a real value– Maintained illuminance must equal or exceed design

illuminance in a successful system


Design Tool: Lookup Tables

product driven and for a specific lamp-luminaire combination—

in this case a recessed can-type downlight

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Design Tool: Sample Layout

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Design Tool:Zonal Cavity

Method

this method applies ONLY

to uniformilluminance

situations and is embodied in a worksheet >>


Zonal Cavity Method:The Bottom Line

# luminaires =

(illuminance) (area)(lumens per luminaire) (CU) (LLF)

where, illuminance = design illuminanceCU = coefficient of utilizationLLF = light loss factor area = task (lighted) arealumens per luminaire = lamp lumens x lamps per fixture

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Zonal Cavity Method:A Second Bottom Line

maintained illuminance =

(# luminaires)(lumens per luminaire)(CU)(LLF)(area)

where, # luminaires = a realistic design luminaire countlumens per luminaire = lamp lumens x lamps per fixtureCU = coefficient of utilizationLLF = light loss factor area = task area


Zonal Cavity Method:An Unstated Bottom Line

initial illuminance =

(# luminaires)(lumens per luminaire)(CU)(1)(area)

where, # luminaires = a realistic design luminaire countlumens per luminaire = lamp lumens x lamps per fixtureCU = coefficient of utilizationLLF = has been set to 1.0 area = task area

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Zonal Cavity Method:Key Metrics

CU = coefficient of utilization

-- the efficiency (lumens/lumens) of a particular luminaire installed in a particular space in delivering light from lamps to task

-- is dimensionless (decimal value)

-- 0.65 means 65% of lamp light reaches task


Zonal Cavity Method:Key Metrics

LLF = light loss factor(s)

-- LLF collectively represents several factors that will cause a deviation between initial and maintained illuminance

-- dimensionless (decimal value)

-- 0.75 LLF means a 25% loss

-- total LLF = product of individual LLFs

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Light Loss Factors

Fixed (non-recoverable) factors– Non-standard voltage

– Non-standard ballast

– Non-standard ambient temperature

– these factors essentially adjust lamp/ballast performance to account for non-catalog conditions; these effects are generally constant over time (they don’t escalate; and they can’t be mitigated by normal maintenance)


Light Loss Factors

Progressive (recoverable) factors– Burnouts– Lamp lumen depreciation– Luminaire dirt depreciation– Room surface dirt depreciation– Luminaire surface depreciation

– these factors essentially adjust illuminance estimates to account for wear and tear over time; the effects change over time (and can be reversed … at a cost)

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Zonal CavityMethod

general data

correlators

LLFs

calculations


Zonal Cavity Walkthrough

start with design illuminance; luminaire selection (a trial selection); and lamp selection (perhaps also a trial)

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select a luminaire (from IESNA Lighting Handbook, textbook, or web site); find CU data for the fixture … after the correlating factors are assembled



the IESNA Lighting Handbook, has typical CU data (and more information) for many genericfixture types; manufacturers’www sites will have specific fixture CU data

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initial luminaire selection will be based upon meeting some design criteria; these criteria can be roughly evaluated from sampleluminaire data

photometrics

basic properties

cross section

CU values



find lamp data; from generic tables or manufacturer’s catalog informationfor zonal cavity method need initial lumens and lumen maintenance (lamp LLF)

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define space geometry and reflectances, calculate thecorrelation variables (cavity ratios and effective reflectances); determine the CU value



extracting CU values—to do so you need to knowRCR, rhocc, and rhow (rhofc is assumed to be 20%) – see next slides

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start with space dimensions (L, W, and H of three “cavities”)



calculate cavity ratios for three cavities using above equations (or look-up tables)a non-existent cavity has a ratio of “0” (h = 0)

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cavity ratios can be calculated for non-rectilinear spaces usinga more basic equation



wall reflectance (rhow) is the weighted average reflectance of wall surfacesrho = visible reflectance (%)area = surface area1, 2, … are different finishes or materials in the cavity being considered

rhow = (rho1)(area1) + (rho2)(area2) + …

area1 + area2 + …

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establish effective cavity reflectances for ceiling and floor cavities—using this chart; ceiling/floor reflectance, wall reflectance, and cavity ratio are variables



CU adjustment factors are used if floor cavity reflectance (rhofc) is not 20%

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CU values are extracted from data tables on the basis of rhocc, rhow, and RCR

in this case from manufacturer’s catalog data

note the spacing criterion (SC) value (near top of table)

spacing criterion is the maximum distance luminaires may bespaced apart (usually taken as center line to center line)

if illuminance is to be reasonably uniform; given as a multpile of mounting height above task



establish LLF values

LLFtotal = (LLF1) (LLF2) (…)

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Lamp Lumen DepreciationGeneric: select a reasonable valuefor the chosen lamp typeSpecific: obtain from manufacturer’s catalog


Zonal Cavity WalkthroughLuminaire Dirt Depreciationa multi-step process first, establishing categories

luminaires (fixtures) will getdirty (collect dust / attract grime)over time; such dirtiness willreduce the performance of the luminaire; different fixturesdo better or worse at stayingclean—thus this particular LLF

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Luminaire Dirt Depreciation(continued) then, establishing environmental dirt conditions



Luminaire Dirt Depreciation(continued) another way of establishing environmental dirt conditions

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Luminaire Dirt Depreciation (continued) select a reasonable value for chosen luminaire type (category), considering environmental dirt conditions (VC to VD) and cleaning schedule (months)



System Voltage Effect (LLF) establishing building voltage impact on lamp output

substantial effect

little effect

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crunch numbers

a) theoretical # fixtures requiredb) actual # fixtures desiredc) maintained illuminanced) initial illuminance



theoretical analysis (first cut) yields the precise number of fixtures needed to deliver maintained illuminancethis may be 24.7 (not possible) or 11 (not symmetrical)

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select an architecturally-desired number of fixtures and recalculate illuminance


A Different Design Tool:Point-to-Point Method

• Used with local or supplemental illuminanceapproach

• Requires access to luminous intensity data– from manufacturer’s catalog (specific) – common– from lighting handbooks (generic) – less common

• Requires no information about materials in the space (considers direct illuminance only)

• Requires information about the source-task arrangement

• Should include LLF for lamp lumens/luminaire dirt

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Point-to-Point Method

E = (I) (cos Θ) (LLF) / (d2)

where,

E = illuminance

I = luminous intensity in direction “D”

Θ = angle of incidence

LLF = light loss factor

d = distance (source to task)see next slide for illustration


Design Analysis:Point-to-Point Method

establish situational geometry—

find d (between source and P)

find Θ

P is the illuminated point of interest

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Point-to-Point Method

E = (I) (cos Θ) (LLF) / (d2)

involves the “cosine law” (light spreads over a greater area as the angle of incidence increases)

(cos 0 = 1.0; cos 90 = 0)

and

involves the “inverse square law”(light spreads over a greater area as distance “d” increases)

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Design Analysis:Point-to-Point Method

select luminaire/lamp, thenfind luminous intensity (candlepower) data at appropriate angles (thoseof interest to design)

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there are several formats for luminous intensity data

full polar this slide

quadrant previous slide


LED is NOT – repeat, NOT energy efficient in most applications just yet.There are a few efficient LED products – like the CREE downlight –

and a lot of mediocre, inefficient stuff. Be very selective and don’t believe the marketing hype.

A good place to learn more about the problems of current LED products is the US DOE’s CALIPER reports. James Benya-SBSE listserve (7 Nov 2008)

white LED spectrum (wikimedia)

LED phosphor

electric lighting design analysis tools

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