DAYLIGHTING DESIGNDAYLIGHTING DESIGNDAYLIGHTING DESIGNDAYLIGHTING DESIGN

Stuart Cooley Stuart Cooley Energy Efficiency EngineerEnergy Efficiency Engineer

City of Santa MonicaCity of Santa Monica

January 4, 2008

AgendaAgenda

Nature of LightNature of Light Nature of VisionNature of Vision Light PhysicsLight Physics Units and the language of lightingUnits and the language of lighting DaylightingDaylighting

– HealthHealth– Design Design – ControlsControls

Designing with the SunDesigning with the Sun

Nature of LightNature of Light

Electromagnetic RadiationElectromagnetic Radiation A spectrum of energy frequenciesA spectrum of energy frequencies

– VisibleVisible– Infrared and UltravioletInfrared and Ultraviolet

Electromagnetic SpectrumElectromagnetic Spectrum

Electromagnetic SpectrumElectromagnetic Spectrum

Nature of VisionNature of Vision

The EyeThe Eye– LensLens– RetinaRetina

Rods – respond to light levelRods – respond to light level Cones – provide color informationCones – provide color information

– Adjustable to varying light levelsAdjustable to varying light levels– Optimized for greenOptimized for green

Eye and Color ReceptionEye and Color Reception

Pupil

Iris

Retina: Layer within globe containing Rods and Cones

Fovea: Central point of vision - Cones Only

Both Rods and Cones respond to color. Only Cones provide color information to the brain

Lens

Credit: Stan Walerczyk

Rod and Cone DistributionRod and Cone DistributionNotes:

1. No Rods in the Fovea

2. Rods outnumber cones 10 to 1 outside of Fovea

3. Rods and Cones differ in the way they respond to light spectrum

4. We need to understand how rods and cones respond to color in order to define lighting in meaningful termsCredit: Stan Walerczyk

Photopic Function:Photopic Function:– Shows spectral response of the Shows spectral response of the

ConesCones – In order to isolate the cones, In order to isolate the cones,

researchers had to limit the field of researchers had to limit the field of view to the foveaview to the fovea

Photopic FunctionPhotopic Function

2º Field of View

Fovea – Cones ONLY

Credit: Stan Walerczyk

Scotopic FunctionScotopic Function

Scotopic Function:Scotopic Function:– Shows spectral response of the Shows spectral response of the

RodsRods– Isolation of the rods required a very Isolation of the rods required a very

dark environment with off-axis dark environment with off-axis target target

Very low- luminance target

Off-Axis dark-adapted rods

Credit: Stan Walerczyk

Scotopic and Photopic Scotopic and Photopic FunctionsFunctions

V’()

V()

Credit: Stan Walerczyk

Spectral LuminousSpectral LuminousEfficiency FunctionsEfficiency Functions

V’()

V()

Scotopic

Photopic

400 nm 700 nm

The light source impact on Rods is defined by the Scotopic Function – peaks in blue region

The light source impact on Cones is defined by the Photopic Function – peaks in green region

Credit: Stan Walerczyk

Scotopic vision to save Scotopic vision to save energyenergy Scotopic Function defines Rod response Scotopic Function defines Rod response

Rods are the main controller of pupil sizeRods are the main controller of pupil size

Rods are active at normal interior light levelsRods are active at normal interior light levels

More scotopic color in light = smaller pupilsMore scotopic color in light = smaller pupils

Smaller pupils = better visual acuity and Smaller pupils = better visual acuity and higher levels of brightness perceptionhigher levels of brightness perception

These are important considerations in many These are important considerations in many working environments, especially with VDTsworking environments, especially with VDTs

Credit: Stan Walerczyk

Light PhysicsLight Physics

PhotonsPhotons– Energy released when excited Energy released when excited

electrons drop back down in their electrons drop back down in their atomic shellsatomic shells

Described by frequency “packets”Described by frequency “packets” Sunlight = “full spectrum”Sunlight = “full spectrum”

Light PhysicsLight Physics

Light is either absorbed, Light is either absorbed, transmitted, or reflectedtransmitted, or reflected

Light is refracted when the wave Light is refracted when the wave travels through a change in travels through a change in densitydensity

Light frequencies separated when Light frequencies separated when refractedrefracted

Visible SpectrumVisible Spectrum

ROY G. BIVROY G. BIV

VIBGYORVIBGYOR

Red orange yellow green blue indigo Red orange yellow green blue indigo violetviolet

Light PhysicsLight Physics

White Light is a combination of White Light is a combination of three “unique colorsthree “unique colors– Red – green – blueRed – green – blue– Cyan – Magenta – YellowCyan – Magenta – Yellow

Black = Absence of light (OR) Black = Absence of light (OR) absorption of all lightabsorption of all light

Light PhysicsLight Physics

Black Body radiationBlack Body radiation– A perfect absorber and re-emitter of A perfect absorber and re-emitter of

lightlight Reflects nothingReflects nothing Transmits nothingTransmits nothing Heats up and re-radiates at its “black-Heats up and re-radiates at its “black-

body temperaturebody temperature

– Sun is a black body at ~6,000 KelvinSun is a black body at ~6,000 Kelvin

Black Body RadiatorsBlack Body Radiators

Sun is White HotSun is White Hot Burning Coal is Red HotBurning Coal is Red Hot

Color TemperatureColor Temperature

Lamps approximate daylightLamps approximate daylight– Cool white fluorescent ~ 4100 KCool white fluorescent ~ 4100 K– Warm White Fluorescent ~ 2700 KWarm White Fluorescent ~ 2700 K– Daylight or Full spectrum lamps ~ Daylight or Full spectrum lamps ~

6000 K6000 K

Sunlight in the Sunlight in the atmosphereatmosphere Blue sky light is scatteredBlue sky light is scattered

– Air is 70% nitrogen, also OAir is 70% nitrogen, also O22, CO, CO22, H, H22OO Setting sun often appears redSetting sun often appears red ““The Green Flash”The Green Flash”

Blue sky is ~ 6000 KBlue sky is ~ 6000 K Direct sun approximated by Direct sun approximated by

incandescence – yellowish lightincandescence – yellowish light

Color Rendering IndexColor Rendering Index

Used for artificial lightingUsed for artificial lighting Scale of 1 to 100Scale of 1 to 100 Incandescence = 100 by Incandescence = 100 by

definitiondefinition Fluorescent lamps 70 – 85Fluorescent lamps 70 – 85

Units and LanguageUnits and Languageof lightingof lighting Lumens (measure of visible light Lumens (measure of visible light

output) – used to rate lampsoutput) – used to rate lamps Lamp = bulbLamp = bulb Luminaire = LampLuminaire = Lamp Fixture = Luminaire – “bulb”Fixture = Luminaire – “bulb” Luminaire = fixture + lampLuminaire = fixture + lamp

Units and LanguageUnits and Languageof lightingof lighting Efficacy = measure of efficiencyEfficacy = measure of efficiency Efficacy in units of Lumens/Watt Efficacy in units of Lumens/Watt Watt = power (input to lamp)Watt = power (input to lamp) Watts IS NOT light intensityWatts IS NOT light intensity

Units and LanguageUnits and Languageof lightingof lighting Illuminance = Brightness levelsIlluminance = Brightness levels Illuminance in units of lumens per Illuminance in units of lumens per

square foot = foot-candlessquare foot = foot-candles OR Illuminance in units of lumens OR Illuminance in units of lumens

per square meter = “lux” per square meter = “lux”

EfficacyEfficacy

Lumens per WattLumens per Watt

Incandescents 5 to 20Incandescents 5 to 20 Fluorescents 60 – 80Fluorescents 60 – 80

LEDs approaching 80LEDs approaching 80

Illuminance (foot-Illuminance (foot-candles)candles) Lumens per square footLumens per square foot

Moonlight 0 to 2 fcMoonlight 0 to 2 fc Office setting 50 – 100 fcOffice setting 50 – 100 fc Daytime 5000 – 10000 fcDaytime 5000 – 10000 fc

DaylightingDaylighting

DaylightDaylight

Affects moodAffects mood Increases productivityIncreases productivity Increases performanceIncreases performance Improves healing timeImproves healing time Encourages buyingEncourages buying

Affects moodsAffects moods

Suicide rate is higher in Sweden, Suicide rate is higher in Sweden, e.g. due to long winterse.g. due to long winters

SAD = Seasonal Affective SAD = Seasonal Affective DisorderDisorder

Affect on productivity

Affect on educationAffect on education

Students learn 20-26% faster in Students learn 20-26% faster in daylit rooms.daylit rooms.

Affect on healingAffect on healing

Light increased healing time by days in hospital study

Affect on salesAffect on sales

Heschong-Mahone Study (for PG&E) on retail daylighting:– Retail sales are 40% higher in day-lit

shops!Source: http://www.h-m-g.com/toppage11.htm#Skylighting and Retail

Sales

WAL-MART Eco-Store in Lawrence KS

Stop & ShopStop & ShopFoxboro, MAFoxboro, MA

•38% energy savings•Higher per cart sales•Improved customer satisfaction•Preferred by employees

•38% energy savings•Higher per cart sales•Improved customer satisfaction•Preferred by employees

Skylights: 60–90% Daylight Courtesy: A.Lovins

Worker Productivity

Occupants’ Salaries, w/o Equip’t & Benefits, are 85–92% of the Cost of Office Operation

Data from Building Owners and Managers Association: Electric Power research Institute, Statistical Abstract of the United States, 1991Data from Building Owners and Managers Association: Electric Power research Institute, Statistical Abstract of the United States, 1991

Daylight DesignDaylight Design

Use the sunUse the sun Limit the sun’s direct componentLimit the sun’s direct component Control “bounce” lightControl “bounce” light Balance heat gain, illuminance Balance heat gain, illuminance

levels, contrast ratioslevels, contrast ratios Be spectrally selectiveBe spectrally selective

Daylight DesignDaylight Design

Perimeter lighting (atriums, Perimeter lighting (atriums, lightwells)lightwells)

Overhangs, finsOverhangs, fins Light shelvesLight shelves Shade controls (shutters)Shade controls (shutters) Monitors, clerestories, skylightsMonitors, clerestories, skylights

Fenestration (glazing)Fenestration (glazing)

Fenestration – dual and triple glazingFenestration – dual and triple glazing Low E film or coatingsLow E film or coatings Argon or krypton filledArgon or krypton filled Visible Light Transmittance Visible Light Transmittance ReflectanceReflectance

SHGC or SC & U-value & VLTSHGC or SC & U-value & VLT

Fenestration (glazing)Fenestration (glazing)

SHGC or SCSHGC or SC– Solar Heat Gain CoefficientSolar Heat Gain Coefficient– Shading Coefficient (~.89 x SHGC)Shading Coefficient (~.89 x SHGC)

U-value - heat conductivity, U-value - heat conductivity, opposite of R-value (heat opposite of R-value (heat resistance), Low U-value, 0.25, is resistance), Low U-value, 0.25, is goodgood

VLT = Visible Light Transmittance (1 VLT = Visible Light Transmittance (1 to 100%) 70 is goodto 100%) 70 is good

Values depend on climateValues depend on climate

Site ConsiderationsSite Considerations

OrientationOrientation– Santa Monica grid 46Santa Monica grid 46°° off north – all off north – all

windows get sunwindows get sun Solar AccessSolar Access

– Microclimate (e.g. morning fog)Microclimate (e.g. morning fog)– Shading from geographyShading from geography– Reflective surfaces (e.g. ocean, pavement)Reflective surfaces (e.g. ocean, pavement)– Neighboring structures (e.g. buildings)Neighboring structures (e.g. buildings)– Trees and landscapingTrees and landscaping

Daylighting DesignDaylighting Design

ShadingShading– Shade south windowsShade south windows– Plant deciduous treesPlant deciduous trees– Awnings, trellises, overhangs, light Awnings, trellises, overhangs, light

shelvesshelves– Vertical fins on east and westVertical fins on east and west– Exterior shade devicesExterior shade devices

Arcades, colonnades, arborsArcades, colonnades, arbors

OverhangsOverhangs

Depth and shape Depth and shape mattermatter

Contrast ratiosContrast ratios

= Ratio of illuminances between = Ratio of illuminances between two objects in same viewtwo objects in same view

3:1 is design goal for visual 3:1 is design goal for visual comfortcomfort

> 10:1 is intolerable (e.g. bright > 10:1 is intolerable (e.g. bright window in dark room)window in dark room)

Daylighting Design Daylighting Design (cont’d)(cont’d) Fenestration (glazing options)Fenestration (glazing options) Locate and size windows Locate and size windows

appropriatelyappropriately North: excellent for daylightingNorth: excellent for daylighting South: low E, high VT, low USouth: low E, high VT, low U East: requires solar controlEast: requires solar control West: requires solar controlWest: requires solar control

Don’t steal the view planes!Don’t steal the view planes!

Daylight should not Daylight should not compete with viewcompete with view

Daylighting Design Daylighting Design (cont’d)(cont’d) Fenestration (windows or glazing)Fenestration (windows or glazing)

– Low emissivity (low E)Low emissivity (low E)– High visible transmittanceHigh visible transmittance– Low U-valueLow U-value– High shading coefficientHigh shading coefficient– Fritted or frosted glassFritted or frosted glass

Daylighting Design Daylighting Design (cont’d)(cont’d) Roof elementsRoof elements

– SkylightsSkylights– ClerestoriesClerestories– MonitorsMonitors– Skylights with louvers (Getty)Skylights with louvers (Getty)

Roof element typesRoof element types

SkylightSkylight

Clerestory Clerestory

MonitorMonitor

SawtoothSawtooth

Variable aperture Variable aperture skylightskylight

Splayed openingSplayed opening

Distributes light better; reduces glare and contrast ratios

Daylighting Control Daylighting Control TechniquesTechniques Interior window treatmentsInterior window treatments

– ShadesShades– BlindsBlinds– CurtainsCurtains– Motorized shadesMotorized shades– Integrated blindsIntegrated blinds

Shading devicesShading devices

Shading devices – Shading devices – Venetian blindsVenetian blinds

Daylighting Control Daylighting Control TechniquesTechniques Lighting SystemsLighting Systems

– Photocell controlled dimmingPhotocell controlled dimming Bi-level dimmingBi-level dimming Continuous dimmingContinuous dimming

– Perimeter - SwitchedPerimeter - Switched– Task-ambient lightingTask-ambient lighting

Lighting Control Lighting Control TechniquesTechniques Lighting SystemsLighting Systems

– TimersTimers– Twist timersTwist timers– Energy Management SystemsEnergy Management Systems– Direct Load ControlDirect Load Control– Utility sponsored DLCUtility sponsored DLC

Overcast skiesOvercast skies

Overcast skiesOvercast skies

ExamplesExamples

Rocky Mountain Institute Rocky Mountain Institute

ExamplesExamples

Public Safety FacilityPublic Safety Facility

ExamplesExamples

Colorado CourtColorado Court

ExamplesExamples

Freiburg (Germany) HomeFreiburg (Germany) Home

ExamplesExamples

NREL (Golden, CO)NREL (Golden, CO)

ExamplesExamples

Solar Rondavel, Thaba-Tseka, Lesotho

Daylighting SummaryDaylighting Summary

Most basic, effective, low-cost way Most basic, effective, low-cost way to integrate high levels of energy to integrate high levels of energy saving and comfort-improving saving and comfort-improving design into a project is with design into a project is with daylighting and passive solar daylighting and passive solar design.design.

Rediscover old world ideas.Rediscover old world ideas. Let the sun do its job and no more.Let the sun do its job and no more.