DAYLIGHTING DESIGN Stuart Cooley Energy Efficiency Engineer City of Santa Monica January 4, 2008

Agenda Nature of Light Nature of Light Nature of Vision Nature of Vision Light Physics Light Physics Units and the language of lighting Units and the language of lighting Daylighting Daylighting –Health –Design –Controls Designing with the Sun Designing with the Sun

Nature of Light Electromagnetic Radiation Electromagnetic Radiation A spectrum of energy frequencies A spectrum of energy frequencies –Visible –Infrared and Ultraviolet

Electromagnetic Spectrum

Nature of Vision The Eye The Eye –Lens –Retina Rods – respond to light level Rods – respond to light level Cones – provide color information Cones – provide color information –Adjustable to varying light levels –Optimized for green

Eye 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 Distribution Notes: 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 terms Credit: Stan Walerczyk

Photopic Function: Photopic Function: –Shows spectral response of the Cones –In order to isolate the cones, researchers had to limit the field of view to the fovea Photopic Function 2º Field of View Fovea – Cones ONLY Credit: Stan Walerczyk

Scotopic Function Scotopic Function: Scotopic Function: –Shows spectral response of the Rods –Isolation of the rods required a very dark environment with off-axis target Very low- luminance target Off-Axis dark- adapted rods Credit: Stan Walerczyk

Scotopic and Photopic Functions V’( ) V( ) Credit: Stan Walerczyk

Spectral Luminous Efficiency Functions V’( ) V( ) Scotopic Photopic 400 nm700 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 energy Scotopic Function defines Rod response Scotopic Function defines Rod response Rods are the main controller of pupil size Rods are the main controller of pupil size Rods are active at normal interior light levels Rods are active at normal interior light levels More scotopic color in light = smaller pupils More scotopic color in light = smaller pupils Smaller pupils = better visual acuity and higher levels of brightness perception Smaller pupils = better visual acuity and higher levels of brightness perception These are important considerations in many working environments, especially with VDTs These are important considerations in many working environments, especially with VDTs Credit: Stan Walerczyk

Light Physics Photons Photons –Energy released when excited electrons drop back down in their atomic shells Described by frequency “packets” Described by frequency “packets” Sunlight = “full spectrum” Sunlight = “full spectrum”

Light Physics Light is either absorbed, transmitted, or reflected Light is either absorbed, transmitted, or reflected Light is refracted when the wave travels through a change in density Light is refracted when the wave travels through a change in density Light frequencies separated when refracted Light frequencies separated when refracted

Visible Spectrum ROY G. BIV ROY G. BIV VIBGYOR VIBGYOR Red orange yellow green blue indigo violet Red orange yellow green blue indigo violet

Light Physics White Light is a combination of three “unique colors White Light is a combination of three “unique colors –Red – green – blue –Cyan – Magenta – Yellow Black = Absence of light (OR) absorption of all light Black = Absence of light (OR) absorption of all light

Light Physics Black Body radiation Black Body radiation –A perfect absorber and re-emitter of light Reflects nothing Reflects nothing Transmits nothing Transmits nothing Heats up and re-radiates at its “black-body temperature Heats up and re-radiates at its “black-body temperature –Sun is a black body at ~6,000 Kelvin

Black Body Radiators Sun is White Hot Sun is White Hot Burning Coal is Red Hot Burning Coal is Red Hot

Color Temperature Lamps approximate daylight Lamps approximate daylight –Cool white fluorescent ~ 4100 K –Warm White Fluorescent ~ 2700 K –Daylight or Full spectrum lamps ~ 6000 K

Sunlight in the atmosphere Blue sky light is scattered Blue sky light is scattered –Air is 70% nitrogen, also O 2, CO 2, H 2 O Setting sun often appears red Setting sun often appears red “The Green Flash” “The Green Flash” Blue sky is ~ 6000 K Blue sky is ~ 6000 K Direct sun approximated by incandescence – yellowish light Direct sun approximated by incandescence – yellowish light

Color Rendering Index Used for artificial lighting Used for artificial lighting Scale of 1 to 100 Scale of 1 to 100 Incandescence = 100 by definition Incandescence = 100 by definition Fluorescent lamps 70 – 85 Fluorescent lamps 70 – 85

Units and Language of lighting Lumens (measure of visible light output) – used to rate lamps Lumens (measure of visible light output) – used to rate lamps Lamp = bulb Lamp = bulb Luminaire = Lamp Luminaire = Lamp Fixture = Luminaire – “bulb” Fixture = Luminaire – “bulb” Luminaire = fixture + lamp Luminaire = fixture + lamp

Units and Language of lighting Efficacy = measure of efficiency Efficacy = 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 intensity Watts IS NOT light intensity

Units and Language of lighting Illuminance = Brightness levels Illuminance = Brightness levels Illuminance in units of lumens per square foot = foot-candles Illuminance in units of lumens per square foot = foot-candles OR Illuminance in units of lumens per square meter = “lux” OR Illuminance in units of lumens per square meter = “lux”

Efficacy Lumens per Watt Lumens per Watt Incandescents 5 to 20 Incandescents 5 to 20 Fluorescents 60 – 80 Fluorescents 60 – 80 LEDs approaching 80 LEDs approaching 80

Illuminance (foot-candles) Lumens per square foot Lumens per square foot Moonlight 0 to 2 fc Moonlight 0 to 2 fc Office setting 50 – 100 fc Office setting 50 – 100 fc Daytime 5000 – fc Daytime 5000 – fc

Daylighting

Daylight Affects mood Affects mood Increases productivity Increases productivity Increases performance Increases performance Improves healing time Improves healing time Encourages buying Encourages buying

Affects moods Suicide rate is higher in Sweden, e.g. due to long winters Suicide rate is higher in Sweden, e.g. due to long winters SAD = Seasonal Affective Disorder SAD = Seasonal Affective Disorder

Affect on productivity

Affect on education Students learn 20-26% faster in daylit rooms. Students learn 20-26% faster in daylit rooms.

Affect on healing Light increased healing time by days in hospital study

Affect on sales Heschong-Mahone Study (for PG&E) on retail daylighting: – –Retail sales are 40% higher in day-lit shops! Source: and Retail Sales WAL-MART Eco-Store in Lawrence KS

Stop & Shop Foxboro, 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, 1991

Daylight Design Use the sun Use the sun Limit the sun’s direct component Limit the sun’s direct component Control “bounce” light Control “bounce” light Balance heat gain, illuminance levels, contrast ratios Balance heat gain, illuminance levels, contrast ratios Be spectrally selective Be spectrally selective

Daylight Design Perimeter lighting (atriums, lightwells) Perimeter lighting (atriums, lightwells) Overhangs, fins Overhangs, fins Light shelves Light shelves Shade controls (shutters) Shade controls (shutters) Monitors, clerestories, skylights Monitors, clerestories, skylights

Fenestration (glazing) Fenestration – dual and triple glazing Fenestration – dual and triple glazing Low E film or coatings Low E film or coatings Argon or krypton filled Argon or krypton filled Visible Light Transmittance Visible Light Transmittance Reflectance Reflectance SHGC or SC & U-value & VLT SHGC or SC & U-value & VLT

Fenestration (glazing) SHGC or SC SHGC or SC –Solar Heat Gain Coefficient –Shading Coefficient (~.89 x SHGC) U-value - heat conductivity, opposite of R-value (heat resistance), Low U- value, 0.25, is good U-value - heat conductivity, opposite of R-value (heat resistance), Low U- value, 0.25, is good VLT = Visible Light Transmittance (1 to 100%) 70 is good VLT = Visible Light Transmittance (1 to 100%) 70 is good Values depend on climate Values depend on climate

Site Considerations Orientation Orientation –Santa Monica grid 46 ° off north – all windows get sun Solar Access Solar Access –Microclimate (e.g. morning fog) –Shading from geography –Reflective surfaces (e.g. ocean, pavement) –Neighboring structures (e.g. buildings) –Trees and landscaping

Daylighting Design Shading Shading –Shade south windows –Plant deciduous trees –Awnings, trellises, overhangs, light shelves –Vertical fins on east and west –Exterior shade devices Arcades, colonnades, arbors Arcades, colonnades, arbors

Overhangs

Depth and shape matter

Contrast ratios = Ratio of illuminances between two objects in same view = Ratio of illuminances between two objects in same view 3:1 is design goal for visual comfort 3:1 is design goal for visual comfort > 10:1 is intolerable (e.g. bright window in dark room) > 10:1 is intolerable (e.g. bright window in dark room)

Daylighting Design (cont’d) Fenestration (glazing options) Fenestration (glazing options) Locate and size windows appropriately Locate and size windows appropriately North: excellent for daylighting North: excellent for daylighting South: low E, high VT, low U South: low E, high VT, low U East: requires solar control East: requires solar control West: requires solar control West: requires solar control Don’t steal the view planes! Don’t steal the view planes!

Daylight should not compete with view

Daylighting Design (cont’d) Fenestration (windows or glazing) Fenestration (windows or glazing) –Low emissivity (low E) –High visible transmittance –Low U-value –High shading coefficient –Fritted or frosted glass

Daylighting Design (cont’d) Roof elements Roof elements –Skylights –Clerestories –Monitors –Skylights with louvers (Getty)

Roof element types

Skylight Clerestory Monitor Sawtooth

Variable aperture skylight

Splayed opening Distributes light better; reduces glare and contrast ratios

Daylighting Control Techniques Interior window treatments Interior window treatments –Shades –Blinds –Curtains –Motorized shades –Integrated blinds

Shading devices

Shading devices – Venetian blinds

Daylighting Control Techniques Lighting Systems Lighting Systems –Photocell controlled dimming Bi-level dimming Bi-level dimming Continuous dimming Continuous dimming –Perimeter - Switched –Task-ambient lighting

Lighting Control Techniques Lighting Systems Lighting Systems –Timers –Twist timers –Energy Management Systems –Direct Load Control –Utility sponsored DLC

Overcast skies

Examples Rocky Mountain Institute Rocky Mountain Institute

Examples Public Safety Facility Public Safety Facility

Examples Colorado Court Colorado Court

Examples Freiburg (Germany) Home Freiburg (Germany) Home

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

Examples Solar Rondavel, Thaba-Tseka, Lesotho

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