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Let There be Light Let There be Light Let There be Light: Let There be Light: Climatic Considerations Climatic Considerations in Medieval Stained in Medieval Stained Gl A th ti Gl A th ti Glass Aesthetics Glass Aesthetics

Chris Simmons Chris Simmons D L M k D L M k

• Dr. Lawrence Mysak,
• Dr. Lawrence Mysak,

McGill University McGill University

International Congress on International Congress on International Congress on International Congress on Medieval Studies Medieval Studies 11 May, 2008 11 May, 2008

Outline Outline Outline Outline

Motivation and Hypothesis Motivation and Hypothesis Motivation and Hypothesis Motivation and Hypothesis Basic Concepts in Stained Glass Evolution Basic Concepts in Stained Glass Evolution M th d d C t i A hit t l M th d d C t i A hit t l Methods and Concepts in Architectural Methods and Concepts in Architectural Lighting Analysis Lighting Analysis Results Results Conclusions Conclusions Future Work Future Work

Interior Lighting: Motivation Interior Lighting: Motivation

One of the most important elements in gothic design One of the most important elements in gothic design The foundations for the relationship between window sizes The foundations for the relationship between window sizes and prevailing climate (cloudiness) established by Wachs and prevailing climate (cloudiness) established by Wachs (1964) (1964) ( ) ( ) Relationships between stained glass design (coloured v. Relationships between stained glass design (coloured v. white) and climate (cloudiness) has been discussed by white) and climate (cloudiness) has been discussed by ) ( ) y ) ( ) y stained glass art historians such as Charles Sherrill (1927, stained glass art historians such as Charles Sherrill (1927, 1931) 1931) Goal of this research: Goal of this research: to evaluate quantitatively the overall to evaluate quantitatively the overall daylighting performance of cathedrals with original stained daylighting performance of cathedrals with original stained glass from different epochs under cloudy and sunny glass from different epochs under cloudy and sunny conditions to see if the climate relationship to stained conditions to see if the climate relationship to stained glass is viable glass is viable

Medieval Interior Medieval Interior Lighting: Primary Lighting: Primary Lighting: Primary Lighting: Primary Sources Sources

Daylighting Daylighting

– Window size (related to Window size (related to hit t l t l ) hit t l t l ) architectural style) architectural style) – Glazing transmission Glazing transmission (strongly controlled by (strongly controlled by

Choir Clerestory of Bourges (top) and Auxerre (bottom)

( g y y ( g y y type of stained glass) type of stained glass) – Time of day, season, Time of day, season, latitude latitude latitude latitude – Cloudy v. Sunny Cloudy v. Sunny

Candlelight (small Candlelight (small g ( g ( contribution) contribution) Open Doors Open Doors

Window Size and Glazing Window Size and Glazing Transmission: England Transmission: England Transmission: England Transmission: England

English churches English churches tended to contain tended to contain both large windows both large windows and often a and often a and often a and often a majority of white or majority of white or

• therwise high
• therwise high
• therwise high
• therwise high

translucency glass, translucency glass, from the early from the early y Thirteenth century Thirteenth century to the Renaissance to the Renaissance

York: Five Sisters Gloucester: Great East Window

Window Size and Glazing Window Size and Glazing Transmission: Mediterranean Transmission: Mediterranean

Mediterranean churches Mediterranean churches Mediterranean churches Mediterranean churches tended to have either tended to have either small windows or small windows or coloured glazing or both coloured glazing or both coloured glazing or both coloured glazing or both Stained Glass historians Stained Glass historians Ch l Sh ill Ch l Sh ill Charles Sherrill, Charles Sherrill, Meredith Lillich and Meredith Lillich and

• thers have postulated
• thers have postulated

th t th d t th t th d t that these are due to that these are due to England’s cloudier England’s cloudier climate and the climate and the M dit ’ M dit ’

Toledo

Mediterranean’s sunny Mediterranean’s sunny climate, respectively climate, respectively

European Cloud Climatology European Cloud Climatology

March, 1990 March, 1990-

• 2003

2003 NAO+ years NAO+ years NAO years NAO years Strong latitudinal Strong latitudinal gradient over gradient over gradient over gradient over France France

Long-Term Average Percent of Total Cloud Cover, from Meerkötter et al. (2004)

Northern Continental Glass Northern Continental Glass

Full Colour and Mixed Full Colour and Mixed Programs (1100 Programs (1100-

• 1260)

1260) The Grisaille Revolution (1270 The Grisaille Revolution (1270-

• 1350)

1350) Persistence of white glass or Persistence of white glass or Persistence of white glass or Persistence of white glass or translucent glass through the translucent glass through the Renaissance (1600) Renaissance (1600)

Le Mans Cologne Troyes

Methodology Methodology Methodology Methodology

Season: Summer and Winter Observations Season: Summer and Winter Observations Extech 407026 Illuminance meter used for Extech 407026 Illuminance meter used for illuminance illuminance measurements (lux) measurements (lux) Canon Digital Rebel XTi SLR Camera (ISO 100, f Canon Digital Rebel XTi SLR Camera (ISO 100, f-

• stop

stop 4.0, Daylight White Balance) used to produce High 4.0, Daylight White Balance) used to produce High 4.0, Daylight White Balance) used to produce High 4.0, Daylight White Balance) used to produce High Dynamic Range (HDR) images and collect Dynamic Range (HDR) images and collect luminance luminance data (candela/m data (candela/m2), processed by Photosphere (Ward) ), processed by Photosphere (Ward) Interchurch comparison of specific church sectors Interchurch comparison of specific church sectors (ambulatory, transept, nave, choir) (ambulatory, transept, nave, choir)

Luminance vs Illuminance Luminance vs Illuminance Luminance vs. Illuminance Luminance vs. Illuminance

Illuminance Illuminance is the luminous is the luminous Luminance Luminance is the is the Illuminance Illuminance is the luminous is the luminous flux (visible light from many flux (visible light from many directions/second) received directions/second) received

• ver a surface.
• ver a surface.

Luminance Luminance is the is the visible light emitted visible light emitted each second in one each second in one direction from a given direction from a given related to additive related to additive contribution of luminance contribution of luminance (with respect to the (with respect to the direction from a given direction from a given source area source area luminous intensity/area luminous intensity/area ( d l / ( d l /

2)

reflectivity of the material) reflectivity of the material) represents the broad represents the broad ambient lighting received at ambient lighting received at i i t bj t t th i i t bj t t th (candela/m (candela/m2) Brightness Brightness A function of A function of a given point, subject to the a given point, subject to the inverse square law inverse square law A function of A function of reflectance and reflectance and transmittance of transmittance of material material material material

Daylight Factor Daylight Factor Daylight Factor Daylight Factor

Toward ceiling

Interior Horizontal Illuminance Exterior Horizontal Illuminance ________________________ x 100%

In a location with an

Al t t f CIE St d d Al t t f CIE St d d

unobstructed hemispherical sky view

Always constant for CIE Standard Always constant for CIE Standard Overcast Sky 1 (uniformly overcast sky) Overcast Sky 1 (uniformly overcast sky)

Difficulties and Limitations to Difficulties and Limitations to f S f S Methods: No Perfect Solution Methods: No Perfect Solution

No medieval program is complete or perfectly preserved No medieval program is complete or perfectly preserved p g p p y p p g p p y p

– Destruction Destruction of original glazing (war, fire, vault collapse, religious

• f original glazing (war, fire, vault collapse, religious

conflict, general decay and poor maintenance) conflict, general decay and poor maintenance) – Glazing Glazing moved moved to different windows to different windows – Cathedral or program Cathedral or program never completed never completed (due to economic (due to economic constraints), or completed during another epoch in a different style constraints), or completed during another epoch in a different style – Corrosion or blackening Corrosion or blackening of original glass (Chartres Clerestories)

• f original glass (Chartres Clerestories)

l d t l li hti th i i ll i t d d l d t l li hti th i i ll i t d d leads to lower lighting than originally intended leads to lower lighting than originally intended – 19 19th

th century and

century and modern replacement glass modern replacement glass admits more light admits more light than originally intended than originally intended Restoration work Restoration work and scaffolding at time of measurements and scaffolding at time of measurements – Restoration work Restoration work and scaffolding at time of measurements and scaffolding at time of measurements

Different cathedrals have different levels of corrosion and Different cathedrals have different levels of corrosion and d t i ti i i d t i ti i i f ibl f ibl modern contamination, giving us a modern contamination, giving us a range range of possible

• f possible

values rather than a unique solution values rather than a unique solution

Results Results

Chartres and Strasbourg Nave HDF Chartres and Strasbourg Nave HDF g

Bourges Daylight Bourges Daylight F t F t Factors Factors

Bourges S. Ambulatory Clear Sky Bourges S. Ambulatory Clear Sky Illuminance Measurements Illuminance Measurements Illuminance Measurements Illuminance Measurements

Summer (lux) Location Time (GMT) Horizontal West North East South 1 951 11 5 9 25 13 1 951 11 5 9 25 13 2 953 15 7 12 12 21 4 955 12 7 9 12 9 6 957 21 6 15 32 6 957 21 6 15 32

• 7

1000 31 8 24 57

• 9

1001 259 13 22 186 156 Winter (lux) Winter (lux) Location Time (GMT) Horizontal West North East South 1 1040 32 23 24 45 43 2 1042 60 25 27 57 151 4 1101 69 31 27 48 99 6 1048 94 16 17 192 100 7 1051 49 23 18 68 60 9 1054 89 21 17 100 77

Bourges Sunny Measurements Bourges Sunny Measurements

L M Cl Sk L M Cl Sk Le Mans Clear Sky Le Mans Clear Sky Daylighting (Summer Daylighting (Summer y g g ( y g g (

• v. Winter)
• v. Winter)

Winter (lux)

Location Time (GMT) Horizontal West North East South 1 1102-1107 28 14 10 26 19 2 1102-1105 29 15 10 18 15 3 1102-1106 35 18 7 31 18 3 1102 1106 35 18 7 31 18

Summer (lux)

Location Time (GMT) Horizontal West North East South 1 1237 44 26 15 20 23 2 1235 42 25 15 19 23 3 1240 41 25 9 23 26

Le Mans Estimated Daylight Factors Le Mans Estimated Daylight Factors

Contaminations: choir screen Contaminations: choir screen prevents most direct light prevents most direct light penetration from 19 penetration from 19th

th century

century coloured coloured windows of windows of ambulatory, but light from ambulatory, but light from y, g y, g modern nave windows and modern nave windows and large, later clerestories facing large, later clerestories facing the choir in the transept/ the choir in the transept/ crossing crossing

Tours and Cologne Tours and Cologne

Tours Daylight Tours Daylight Factors Factors

Highly Precise Highly Precise Confirms values at other Confirms values at other f ll l i i f ll l i i full colour interiors full colour interiors Strong modern Strong modern contamination from contamination from contamination from contamination from nave/crossing until inner nave/crossing until inner choir choir

Cologne Daylight Factors Cologne Daylight Factors

Tour’s HDFs are Tour’s HDFs are 2/3 to to ½ those of Cologne those of Cologne Cologne brighter, Cologne brighter, despite being a larger despite being a larger and taller cathedral and taller cathedral and taller cathedral and taller cathedral (more distance (more distance between between ceiling/windows and ceiling/windows and g

• bservation plane than
• bservation plane than

at Tours) at Tours) Cologne’s proportions Cologne’s proportions also appear to explain also appear to explain the lack of a strong the lack of a strong ff ff effect due to modern effect due to modern contamination from the contamination from the nave nave

Choir Luminance Maps Choir Luminance Maps Choir Luminance Maps Choir Luminance Maps

Tours, Cloudy Cologne, Cloudy Le Mans, Sunny

Backlighting Backlighting

Grisailles and other white glass provide Grisailles and other white glass provide

St-Ouen Nave: 1504 GMT 26 January, 2008

Grisailles and other white glass provide Grisailles and other white glass provide particularly severe backlighting, rendering particularly severe backlighting, rendering windows illegible and unattractive. This is not as windows illegible and unattractive. This is not as pronounced for most Thirteenth century programs pronounced for most Thirteenth century programs

Cologne Choir: 30 April, 2007 812 GMT

Backlighting Backlighting Backlighting Backlighting

Le Mans Choir: 25 January, 2007 1253 GMT Le Mans South Choir: 3 June, 2007 734 GMT

The Effects of Grisailles on a Full The Effects of Grisailles on a Full Colour Interior: Chartres Ambulatory Colour Interior: Chartres Ambulatory Colour Interior: Chartres Ambulatory Colour Interior: Chartres Ambulatory

Chartres N. Ambulatory, Grisailles are indicated by their bay number, averages between two DF measurements are in black, less precise daylight factors are in grey, and the DFs associated with only one measurement are in pink

Chartres S Ambulatory Chartres S Ambulatory Chartres S Ambulatory Chartres S Ambulatory

Chartres S. Ambulatory, Grisailles are indicated by their bay number, highly precise averages between two DF measurements are in black, average between two less precise measurements are in grey, and the DFs associated with one measurement round on 24 January, 2007 are in pink

Évreux Évreux and St and St-Serevin Serevin (1300 (1300-1500) 1500) Évreux Évreux and St and St Serevin Serevin (1300 (1300 1500) 1500)

St St-

• Ouen and Troyes (Renaissance

Ouen and Troyes (Renaissance ) and Modern) and Modern)

Thirteenth Century and Thirteenth Century and Renaissance Form Illumination Renaissance Form Illumination

Summary of Results Summary of Results Summary of Results Summary of Results

Daylight Factors Factors Early Thirteenth Century 0.02 - 0.05% Grisaille Revolution (Cologne) 0 05 - 0 07% Grisaille Revolution (Cologne) 0.05 0.07% Post-Grisaille Revolution 0.08 - 0.4% Spanish Renaissance Interiors 0.02 – 0.06% Choir form illumination can be Choir form illumination can be 2 - 4 times greater for comparable cloudy skies in a i ill h i h i l th grisaille choir hemicycle than for a full colour hemicycle

Glazing Transmissions: Mosaic v. Glazing Transmissions: Mosaic v. f C f C Fifteenth Century and Modern Fifteenth Century and Modern

Bay 51, Rouen Cathedral

Colour Colour Saturation and Glazing Saturation and Glazing Transmission: Romanesque v Transmission: Romanesque v Transmission: Romanesque v. Transmission: Romanesque v. Gothic Gothic

Bay 30, Chartres Cathedral Cathedral Luminance Scale: 0-0.5 cd/m2

Conclusions Conclusions

Daylight factors show a marked improvement in overcast daylighting in Daylight factors show a marked improvement in overcast daylighting in cathedrals built during and after the Grisaille Revolution cathedrals built during and after the Grisaille Revolution Clear sky conditions in choir show similar to greater vault luminances for Clear sky conditions in choir show similar to greater vault luminances for Clear sky conditions in choir show similar to greater vault luminances for Clear sky conditions in choir show similar to greater vault luminances for full colour windows under sunlight as grisaille windows under cloudy skies full colour windows under sunlight as grisaille windows under cloudy skies Sunny skies provide greater overall interior illumination across a large Sunny skies provide greater overall interior illumination across a large y p g g y p g g section of the church than most cloudy events (esp. choir) section of the church than most cloudy events (esp. choir) Winter season provides the greatest contrast between overcast and clear Winter season provides the greatest contrast between overcast and clear sky conditions sky conditions sky conditions sky conditions Fifteenth and Sixteenth century glazing transmits just under an order of Fifteenth and Sixteenth century glazing transmits just under an order of magnitude more light than Thirteenth century mosaic glass; Romanesque magnitude more light than Thirteenth century mosaic glass; Romanesque g g y g ; q g g y g ; q glass is more transmissive than saturated Gothic glass glass is more transmissive than saturated Gothic glass Backlighting in sunny conditions is significant for grisaille Backlighting in sunny conditions is significant for grisaille-

• dominated and

dominated and Renaissance interiors but is hardly notable for full colour cathedrals Renaissance interiors but is hardly notable for full colour cathedrals Renaissance interiors but is hardly notable for full colour cathedrals Renaissance interiors but is hardly notable for full colour cathedrals

Important Considerations beyond Important Considerations beyond Climate Climate Climate Climate

Economic Factors (Cost of work in coloured glass) Economic Factors (Cost of work in coloured glass) The Formalist Argument (greater lighting of architectural The Formalist Argument (greater lighting of architectural forms) forms) The Nature of Theological Discourse (Lillich, 2000) The Nature of Theological Discourse (Lillich, 2000) Technological Improvements (larger panes, more Technological Improvements (larger panes, more translucent glass) translucent glass) Backlighting Backlighting Non Non-climatic changes in aesthetic tastes climatic changes in aesthetic tastes Non Non-climatic changes in aesthetic tastes climatic changes in aesthetic tastes

Future Work Future Work Future Work Future Work

Modelling of Cathedrals, with Modelling of Cathedrals, with estimation of original glazing estimation of original glazing estimation of original glazing estimation of original glazing transmissions transmissions More measurements in Great More measurements in Great Britain (York, Gloucester, Britain (York, Gloucester, Lincoln, Salisbury, and Lincoln, Salisbury, and Canterbury) and Italy Canterbury) and Italy (Florence, Siena, Assisi, (Florence, Siena, Assisi, ( , , , ( , , , Arezzo) Arezzo) Another round of Another round of measurements in some measurements in some measurements in some measurements in some interiors to ensure consistency interiors to ensure consistency in DFs (Chartres, Evreux, in DFs (Chartres, Evreux, Bourges) Bourges)

From Wallace et al., Computer Graphics, 1989

Acknowledgements Acknowledgements Acknowledgements Acknowledgements

• Dr. Jennifer Veitch
• Dr. Jennifer Veitch, Technical Advisor Indoor Lighting National

, Technical Advisor Indoor Lighting National Research Council of Canada Technical Advisor Research Council of Canada Technical Advisor Research Council of Canada, Technical Advisor Research Council of Canada, Technical Advisor

• Dr. Chantal Arsenault
• Dr. Chantal Arsenault, Technical AdvisorIndoor Lighting National

, Technical AdvisorIndoor Lighting National Research Council of Canada, Technical Advisor Research Council of Canada, Technical Advisor

• Dr. Duygu Cetegen
• Dr. Duygu Cetegen, Indoor Lighting National Research Council of

, Indoor Lighting National Research Council of C d T h i l Ad i C d T h i l Ad i Canada, Technical Advisor Canada, Technical Advisor

• Dr. Christoph Reinhart
• Dr. Christoph Reinhart, Indoor Lighting National Research Council

, Indoor Lighting National Research Council

• f Canada, Technical Advisor
• f Canada, Technical Advisor

Dr David Covo Dr David Covo McGill University McGill University

• Dr. David Covo
• Dr. David Covo, McGill University

, McGill University Robert Robert and Teresa Simmons and Catherine Thauer and Teresa Simmons and Catherine Thauer, Volunteer , Volunteer Assistants Assistants The Dr. Richard H. Tomlinson Fellowship The Dr. Richard H. Tomlinson Fellowship