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The daylit area e Correlating architectural student assessmentswith current and emerging daylight availability metrics

Christoph F. Reinhart*, Daniel A. WeissmanHarvard University, Graduate School of Design, Cambridge, MA 02138, USA

a r t i c l e i n f o

Article history:Received 2 September 2011Received in revised form26 October 2011Accepted 29 October 2011

Keywords:Daylighting metricsOccupant evaluationsLEEDDaylight simulationsDaysimRadiance

a b s t r a c t

This paper proposes a method for testing current and emerging daylight availability metrics such asdaylighting factor, daylight autonomy, useful daylight illuminance and LEED 3.0 requirements againstbuilding occupant assessments of a daylit space. During spring 2011 the method was tested as a class-room exercise by 60 architectural students enrolled in two graduate-level building science courses in the2nd floor studio space of le Corbusier’s Carpenter Center in Cambridge, MA, USA. The results from thistest yielded that the Lighting Measurement protocol for Spatial Daylight Autonomy, that is current beingdeveloped by the Illuminating Engineering Society of North America (IESNA) daylighting metricscommittee, reproduced the student assessments of the daylit area in the space more reliably than theother tested daylight availability metrics. These findings are preliminary and still need to be validatedand refined in other spaces. Apart from providing valuable data points for scientific experiments, themethod also has substantial educational value as a teaching exercise for architectural students to developan intuitive understanding of contemporary daylight performance metrics, as well as a feeling of howtheir personal lighting preferences compare to these metrics.

� 2011 Elsevier Ltd. All rights reserved.

1. Introduction

What is daylighting, why are we pursuing it, and what is a welldaylit space? The answers to these questions are complex andsubjective. A rather unambiguous response to the first question isthat daylighting describes the controlled use of natural light in andaround buildings. Several drivers exist for why one might want toimplement daylighting. A starting point for most explorations ondaylight is that there must be a certain, program-specific amount ofdaylight available within a space for the space to be called daylit(daylight availability or sufficiency1). To balance occupant comfortand energy concerns, this amount should neither be too low norexcessive. Another frequently voiced requirement is the ability ofbuilding occupants to adapt the (day)light in a space to theirprogrammatic needs. In classrooms and office-type environmentse where occupants do not typically have the freedom to adjusttheir position, and have rather stringent visual comfort require-mentse occupants usually have access tomovable shading controls

to adapt the indoor environment to their needs. In public spaces,such as atria, occupants can adapt bymoving around the space. Thecombination of daylight availability, occupant comfort and energyefficiency leads to a more specific definition of daylighting: A daylitspace is primarily lit with natural light and combines high occupantsatisfaction with the visual and thermal environment with lowoverall energy use for lighting, heating and cooling [1]. The threecategories are linked. For example, when blinds are lowered toavoid discomfort glare, the interior daylight availability is reduced,the electric lighting may be switched on and heating or coolingloads my change accordingly.

Thinking of daylighting in terms of three linked but separatedesign objectives (appropriate light levels, occupant comfort andbuilding energy use) can help designers to work on one objective ata time. In order to do so,metrics are required to reliably evaluate thedesign intent of each category. The objective of this paper is to testthe first category, i.e. how contemporary daylight availabilitymetrics compare with occupant evaluations of a daylit space.

2. Review of daylight availability metrics

Avariety of daylight availability metrics based on rules of thumband computer simulations have been proposed in the past. Themost common rule of thumb used to rate daylight availability in

* Corresponding author.E-mail address: [email protected] (C.F. Reinhart).

1 The first author previously used the term daylight availability to describe “howmuch daylight is available in a space over the course of a year” whereas the IESNADaylighting Metrics committee has started to use daylight sufficiency to name thesame concept. In the following, both terms are considered interchangeable.

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Building and Environment 50 (2012) 155e164


a sidelit space is the window-head-height rule of thumb. The rulerelates the distance from floor to the head of a window to how far“adequate, useful and balanced daylight enters the spaces for mostof the year” [2]. A simulation-based validation study of this rule ofthumb for unobstructed facades yielded that “in a standard, office-type sidelit space equipped with venetian blinds, the depth of thedaylit area usually lies between 1 and 2 times the size of the

window-head-height. For spaces such as atria or circulation areasthat are not equipped with movable shading devices, the ratiorange can increase up to 2.5” [2].

The most common computer-based evaluation of daylightavailability to date begins by defining a grid of upward facingsensors offset from the floor (usually at desk height) followed by anevaluation of the daylight at these sensors using various criteria/metrics. The oldest daylight availability metric is daylight factor,defined as the ratio between the illuminance at a sensor pointinside the space to the illuminance at an unshaded, upward facingexterior reference point, under CIE standard overcast sky condi-tions [3]. Since 2001, substantial effort has gone toward thedevelopment of climate-based daylighting metrics [4e7]. Similar todaylight factor, thesemetrics employ a grid of sensor points, but thedaylight availability evaluation is based on illuminance levels undermultiple sky conditions, usually all sky conditions appearing duringhours of the year when a space is occupied.

In order to be of direct use for design evaluations, daylight avail-ability metrics are usually coupledwith a benchmark, or cutoff level,abovewhichapoint in a space isdefined tobe “daylit”. Theusefulnessof benchmarks is that a space can be divided into a daylit and a non-daylit area. For example versions 2.2 and earlier of the popular LEEDgreen building rating system from the US Green Building council,promoted a daylight, or glazing factor of 2% as a minimum bench-mark level [8]. LEEDVersion 3.0 requires aminimum light level of 25footcandles (269lux) on the equinox at 9 am and 3 pm und CIE clearsky conditions [9]. At the time of writing, the Daylight MetricsCommittee of the Illuminating Engineering Society of North Amer-ican (IESNA) was in the process of completing a new LightingMeasurement (LM) protocol that promoted a daylight autonomy (DA)typemetric to characterize daylight availability/sufficiency in spaces[10]. Daylight autonomy is a climate-based metric defined as thepercentage of occupied times in the year during which minimum,program-specific illuminance levels can bemet by daylight alone [4].The IESNA committee currently favors a target illuminance 300luxfor offices, classrooms and library type spaces, occupied hours from8am to 6 pm local clock time. If applicable, venetian blinds are oper-ated hourly to block any direct sunlight into the space. According tothe IESNA LM, a point is considered to be “daylit” if the daylightautonomy exceeds 50% of the occupied times of the year. The LM ispartly based on expert and building occupant surveys in 61 daylitspaces [11]. However, the surveys only addressed overall daylightlevels in the test spaces,without addressing the spatialdistributionofdaylight within these spaces.

Fig. 1. (a) Outside view looking South of the 2nd floor studio space of the Carpentercenter. (b) Inside view looking North of the 2nd floor studio space of the Carpentercenter.

Fig. 2. Assignment given to the students; floor plan of the 2nd floor studio space of the Carpenter center.

C.F. Reinhart, D.A. Weissman / Building and Environment 50 (2012) 155e164156


Another climate-based metric called useful daylight illuminance(UDI) was introduced by Mardaljevic and Nabil in 2005 [5]. UDIlargely resembles DA but defines lower and upper illuminancethresholds of 100lux and 2000lux for daylight to be “useful”. Due tothe two levels, each point in a space has three UDI values: thepercentage of the occupied time when the illuminance at the pointis below 100lux, above 2000lux or in between. In a later paperMardaljevic, Heschong and Lee further subdivided the100e2000lux “useful” UDI bin into a “supplementary”(100e500lux) and an “autonomous” (500e2000lux) range [7]. Inthe simulations below, it is assumed that the daylit area corre-sponds to the “useful” 100e2000lux range.

The present study takes a step back from these theoreticalapproaches toward defining daylight availability and insteadexplores how architectural students, following their own intuition,divide a given sidelit space into a “daylit” and a “non-daylit” area.As described above, traditionally, the use of upward facing illumi-nance measurements has served to make such a distinction. But, tothe authors’ knowledge, the only documented study in whicha group of individuals was asked to intuitively locate the boundaryof the daylit area within real spaces is a technical paper publishedin 1931 [12]. In that study a jury of experts and a group of buildingoccupants evaluated 20 rooms in the UK’s then new governmentbuilding, Whitehall. The jury located the daylit area boundary ataround 0.2 percent of the sky factor (around 10lux target

illuminance).While a recent analysis [13] of the composition of thatjury raised concerns regarding the objectivity of these results,which indeed seem very low, the authors still find the basic studyapproach solid and therefore asked 60 architectural students todraw the boundary of the daylight area in a north facing sidelitspace. Afterward a series of daylight availability metrics werecalculated for the space and the resulting daylit area boundarieswere compared to the student assessments.

Several arguments exist as to why one is actually unlikely to findgood agreement between the illuminance based daylighting metricsmentioned above and occupant assessments. First, work plane illu-minances, the amount of variable light falling on real or virtualsurfaces,maybe considerablydifferent thanwhatwe see, namely lightthat is emitted off a surface toward our eyes (luminance). Second, thehuman eye is weak at detecting absolute illuminance levels, meaningthat even if a test subjectwanted to determine the “300luxboundary”within a space, he or she could not determine this line without an

Fig. 3. Sample assignment result with cross point and cross point illuminance (38lux) and distance to façade (11.7 m).

Fig. 4. Radiance model of the Carpenter center.

Table 1Material descriptions in radiance.

Description Measurement description Radiance materialmodifier

Interior concretesurfaces

CIBSE reflectance guide Void plastic interiorconcrete005 0.25 0.25 0.25 0 0"

Ceiling CIBSE reflectance guide Void plasticgeneric ceiling005 0.8 0.8 0.8 0 0"

Context buildings CIBSE reflectance guide Void plasticoutside facade005 0.35 0.35 0.35 0 0"

Outside ground CIBSE reflectance guide Void plasticoutside ground005 0.2 0.2 0.2 0 0"

Glazing (svis ¼ 82%) Inside and outside illuminancereadings taken at variouslocations around the building

Void glass carpenterglazing003 0.8933 0.8933 0.8933

C.F. Reinhart, D.A. Weissman / Building and Environment 50 (2012) 155e164 157


illuminancemeter. Third, given that skyconditions, andhence interiorlighting levels, are constantly changing, it is unlikely that occupantscan mentally average the location of the 300lux boundary over time,especially fora space inwhich theyhavenot spent a lot of time. Finally,the perception of where the boundary between the daylight and thenon-daylit area lies is likely to have a strong subjective element, sothat different individuals will likely make very different assessments.Despite this series of arguments why current daylight availabilitymetrics and occupant assessmentsmight not correspond, the authorsconducted this experiment because the underlying promise ofdaylight availabilitymetrics is that they do in fact predict the daylit areain spaces. Designers frequently use either of the above outlineddaylight availability metrics to determine where the daylit area liesand what percentage of a space is daylit. This paper thus puts thispromise to a first, direct test in a single space.

At this point it is already important to mention that e beyonda validation of the metrics e introducing students to the concept ofa “daylit area” helps them to better understand the role of daylight

in architectural space as well as to “calibrate” their own assessmentof daylit spaces against current and emerging daylight availabilitymetrics.

3. Methodology

3.1. Student assignments

During spring 2011 the first author taught two semester-longgraduate-level classes to architectural students, a required intro-ductory class on Environmental Technologies in Buildings (6205) andan elective class on Daylighting Buildings (6332). Enrollments forthe classes were 45 and 15 students, respectively. There was nostudent overlap between the two classes. Course 6205 was con-cerned with basic phenomena of heat flow, lighting and acousticswhereas the primary focus of Course 6332 was the study of naturaland electric lighting in an architectural context. At the verybeginning of 6332 and at the beginning of the lighting module in6205 students were given the following assignment.

“A key architectural concept is to divide the floor plan of a buildingor space into a ‘daylit’ and a ‘non-daylit’ area. Within the daylitarea indoor illuminances levels due to natural light should beadequate, useful and balanced for most of the year. In this exerciseyou are asked to follow your own intuition and divide the ‘taped’area of 2nd floor Studio in the Carpenter Center into a daylit and

Table 2Radiance simulation parameters.

Ambientbounces

Ambientdivision

Ambientsampling

Ambientaccuracy

Ambientresolution

Directthreshold

5 1,500 100 0.05 300 0

Fig. 5. Individual and mean daylit boundary for courses 6205 (a) and 6332 (b).



a non-daylit area. Please visit the studio on [date and time range]and individually conduct your assessment without consulting withthe other students. During your visit you will be asked to carry outa series of illuminance measurements and to mark the daylit areaon a floor plan of the space that you will be given.”

The Carpenter Center, which houses Harvard University’sDepartment of Visual and Environmental Studies (VES), wasdesigned by Le Corbusier and completed in 1962 (Fig. 1). As thestudy required that the test space would have both daylit and non-daylit areas, the studio was chosen for its generous room depth of19.5 m from the window plane to the back wall with no obstruc-tions except for a few columns. A north facing space was chosen forthe study to minimize the potential for direct sun during testingand to thus avoid having to consider venetian blinds. The ceiling

height throughout the spacewas 12 feet (3.66m). During their visit,the students were given Tabloid-sized copies of the floor plan(Fig. 2) and initially asked to draw the boundary of the daylit area.The students were then asked to measure illuminance levels atdesk height along the center gridline of the space at intervalscorrelating to the 7 feet (2.12 m) floor grid. The grid was alsoprovided on the plan (dashed lines in Fig. 2) to aid students inobserving their location in space. Note that for consistency, this gridwas also used for the digital analysis (see below). Fig. 3 showsa sample assignment result. The point at which the daylit boundaryline crossed the center gridline is in the following referred to as the“cross point”. Each cross point has an associated illuminance level(based on the students’ illuminance meter readings) and distanceto the North façade as shown in Fig. 3. The cross point illuminance

Fig. 6. Mean boundary lines for 6205, 6332 and total mean boundary line encompassing 164 m2.

Fig. 7. a and b: Distribution of cross point illuminances for 6205 and 6332.



and distance to the façade in Fig. 3 were added later by the authorsto explain the concept.

As a side note, the significance of using the Carpenter Center forthis exercise is not lost on the authors, as Le Corbusier’s climaticanalysis largely relied on intuition in the design and application offorms for daylight modification to create an “espace ineffable.” Inthe Carpenter Center, only the size of the bris soleil was calculated[14]. As this research seeks to help quantify intuition, it seemsappropriate that the test would occur in a space that was alsolargely designed based on intuition.

3.2. Simulations

For the simulation-based analysis of various daylight availabilitymetrics, a detailed digital model of the Carpenter Center anda massing model of surrounding buildings was generated inRhinoceros [15] based on university owned floor plans and sectionsas well as building visits (Fig. 4). Using the DIVA for Rhino plug-in,the model was exported into the validated Radiance/Daysimdaylight simulation programs [16e18]. Daylight factor, interiorilluminance distributions on solstice days at 9 am and 3 pm anddaylight autonomy distributions according to the IESNA RP werecalculated in Radiance/Daysim for the 2nd floor studio using a gridresolution of 0.5 m. For the solstice calculations the standard clearCIE sky with a sun was used via the gensky Radiance program.

Material definitions were set by assessing materials in the actualspace using a CISBE Surface and Reflectance Chart [19]. Directnormal visual transmittances of the glazings were estimatedthrough metering light levels on both sides of the glass (Table 1).The Radiance simulations parameters used are listed in Table 2.

4. Results

4.1. Assignment results

15 students enrolled in GSD course 6332 completed theirassignments on February 14, 2011, a mostly sunny day. On April 4,2011, a mostly overcast day, 45 students enrolled in GSD course6205, repeated the experiment. All participants were asked tomaketheir recordings between 11 am and 2 pm on the given day.Submitted assignments were then digitized and the daylit areaboundaries were traced and compiled using the Adobe CreativeSuite software [20]. After importing all vectors into Rhinoceros,a Grasshopper script was used to assess where all lines intersectedthe Carpenter floor grid [21]. Fig. 5 shows the resulting daylightboundaries. Most boundary lines have the form of an arch that isfurthest away perpendicular to the center of the North facingglazing. On the other hand, a substantial degree of discrepancyexists between the exact location of the boundary lines. The size of

Fig. 8. Distribution of cross point distances to the North facade for 6205 and 6332.

Fig. 9. Comparison of the mean daylit boundary with the window-to-head-height rule of thumb.



the daylit area formed by the façade and the boundary line variesbetween 100 m2 and 248 m2.

In order to determine the “mean daylit boundary” for all studentsubmissions, the following procedure was employed at eachvertical gridline intersection (Fig. 3): The projected distancesbetween the North façade and each boundary line were deter-mined. The mean daylit boundary position was then defined as thearithmetic mean of all of these distances. The resulting mean daylitboundaries for both courses are shown in bold in Fig. 5(a) and (b).Fig. 6 shows themean daylight boundary for both courses as well asfor all samples taken together. The three lines lie surprisingly closetogether with daylight areas ranging from 161 m2 for 6205 to169 m2 for 6332, resulting in an overall mean of 164 m2.

This is actually somewhat surprising given that the two studentgroups evaluated the space under very different sky conditions.Figs. 7 and 8 show the distributions of the cross point illuminancesand the distances to the North façade as defined in Fig. 3 for 6205and 6332, separately. Fig. 7 shows that the illuminances for thecross points were higher for 6332 than for 6205 students due todifferent prevalent sky conditions for both groups. Fig. 8 revealsthat the chosen distances to the North façade were more similar forboth groups. The average cross point illuminance and distance to

the north façade for all students was 144lux at 9.2 m as denoted bythe X in Fig. 8. The mean daylit boundary for all assignments (Fig. 6)will be used in the comparison to daylight availability metricsbelow.

4.2. Comparison to daylight availability metrics

According to the above cited window-head-height rule ofthumb for a space without venetian blinds, the daylit area extendsabout 2e2.5 times the window-head-height into the space. Therulewas originally derived for a straight façade [2]. In order to applyit to the strongly bent North window in the Carpenter Center, thedifferent distance lines were simply drawn as parallel offsets to theglazing. Fig. 9 accordingly compares the mean daylit boundary lineform Fig. 6 with the rule of thumb predictions for various multiplesfrom the façade. It is interesting to see that e except for the regionclose to the left window edge e the mean daylight boundary lieswithin or very close to the range predicted by the zone suggestingthat the rule of thumb is consistent with the user evaluations. Nearthe left edge of the North glazing, the assessments and the rule ofthumb show opposing trends with the mean daylight boundary

Fig. 10. Comparison of the mean daylit boundary with the 2% daylight factor line.

Fig. 11. Comparison of the mean daylit boundary with the 269lux lines under clear sky conditions on September 21st at 9 am and 3 pm.



moving toward the façade. This suggests that the rule of thumbcannot be simply applied to curved glazings as suggested above.

Fig. 10 shows a comparison of the mean daylit boundary linewith the 2% daylight factor line. There is good agreement betweenthe two lines near the left edge of the glazing. But, near the girdcenterline, the daylight factor line lines 28% closer to the façadethan the mean daylit area boundary meaning that the formersubstantially underestimates the size of the daylit area throughoutthe space (122 m2 opposed to 163 m2). This result is somewhatdisappointing for the daylight factor, given that the investigatedspace is north facing and thus barely ever subject to direct sunlight.

Fig. 11 compares the mean daylit boundary line with the 250luxlines under clear sky conditions on September 21st at 9 am and 3pm (LEED 3.0 daylighting credit). While the 9 am LEED line marksan area that is only 7% smaller than the mean daylight area, the 3pm area is 32% larger.

Fig. 12 shows a comparison of the mean daylit boundary withdaylight autonomy predictions for target levels of 150lux, 300luxand 500lux. In accordance with the IESNA RP, the minimumdaylight autonomy level is 50%. The figure shows that the currentlyproposed climate-based daylighting metric is in good agreementwith the subjectively assessed mean daylit area. In fact, the 300lux

predicted daylit area of 152 m2 is only 7% smaller than the meandaylit area proposed by the student evaluations.

Fig. 13 shows a comparison of the mean daylit boundary withUDI predictions for a minimum target level of 50% to mark theboundary of the daylit area. The resulting UDI based daylit area of239 m2 is 46% larger than the daylit area based on the studentassessment. Apart form extending deeper into the space than othermetrics, a fundamental difference is that the UDI based daylit areaexcludes areas right near the North window. Table 3 summarizesthe results for all investigated daylight availability metrics.

5. Discussion

What can the reader learn from these results? First, for theinvestigated space the IESNA daylight autonomy metric and thewindow-head-height rule of thumb both correlate well with the 60student assessments. This result is encouraging for the IESNADaylighting Metrics Committee. The close agreement between therule of thumb and the daylight autonomy calculation are notsurprising given that the rule was previously validated based ondaylight autonomy simulations [2]. For the daylight factor, theresults were substantially smaller than the assessments whereas

Fig. 12. Comparison of the mean daylit boundary with daylight autonomy predictions for target levels of 150lux, 300lux and 500lux. The minimum daylight autonomy level is 50%.

Fig. 13. Comparison of the mean daylit boundary with the UDI100lux-2000lux assuming a boundary level of 50%.



the LEED 3.0 clear sky criterion yielded very different daylit areasfor 9 am and 3 pm. Given that according to LEED a space has tomeeta certain daylit area for both times of day, this result is hard tointerpret andmay point to a certain inconsistency in how the creditis phrased. The daylit area according to the UDI was substantiallylarger than for student assessments.

With a sample size of only one space, it has yet to be determinedwhether these results are of a more general nature. This caveatnotwithstanding, the results for the different daylight availabilitymetrics show that all metrics, except for UDI, mark a daylit area thatextends form the North window into the space which is in line ofhow building occupants think of daylight as “entering a space”. TheUDI, having an upper threshold level, excludes particularly brightareas to alert designers of potential glare or overheating problems.It thus aims to be more than a daylight availability metric andcombine availability, comfort and energy concerns in one [5]. Asexplained in the introduction, the authors feel that it is advanta-geous for designers to break the daylighting problem up into threedistinct categories and check one at a time. This experimentconfirms that this also seems to be how design students (andprobably laypersons as well) intuitively read the daylight in a space.

As already mentioned, the test method described in thismanuscript needs to be applied tomore spaces beforemore generalconclusions can be drawn. Fortunately, the method is simple andinexpensive to carry out in just about any type of publicly acces-sible, daylit space. The authors therefore hope that others willreproduce the experiment, for examplewithin the context of a classor seminar on lighting, and share their results so that the abovementioned preliminary findings can be further tested and refined.

At this point, it is important to note that the daylit boundaryexercise is not merely about providing data points for scientificexperiments but has substantial educational value for participatingstudents. The act of drawing the daylight boundary and thenmeasuring illuminance levels along a central gridline has thepedagogical advantage that students develop a feeling for how 300or 500lux “looks like”. They also learn what their personal lightingpreferences are and how they compare to others. In the era ofincreased reliance on digital design tools, it is imperative thatnovice users gain, quickly and early on, an intuitive understandingof performance metrics so as to be able to make informed designdecisions. This intuition may only occur through direct experience.For example, the student in Fig. 3 learned that he or she preferstarget threshold student levels of 38lux in a studio space such asthe Carpenter Center. That student could then use this target levelduring daylight autonomy simulations. In the authors’ experience,this type of fast and hands-on assignment tends to be popularamong architectural students as it provides tangible feedback thatcan be applied in studio projects.

A necessary condition for the proposed daylight boundaryassessment method to be scientifically valid is that it yieldsreproducible results. Again, these first results are encouragingbecause the two student groups tended to choose very similar

daylit area boundaries, even though they visited the space undersunny and overcast sky conditions as explained above. Anotheropen question is whether architectural students are prone to makedifferent assessments than “laymen” building occupants. Theauthors believe that this is probably not the case because e whilearchitectural students might generally have more developedsensibilities toward lighting than average occupants e the conceptof the daylit area is an everyday concept that is more linked to spaceuse and personal expectation than design theory. Yet anotherquestion to be explored is whether the static 300lux target illu-minance currently proposed by the IESNA Daylighting MetricsCommittee for offices, classrooms and libraries needs to be adjustedaccording to program.

6. Conclusion

Regardless of a computer algorithm’s sophistication, at the endof the day, recommended practices and digital models exist to testconditions in reality, and provide feedback for design. It is stillunclear how such metrics stand up to the realities and nuances ofhuman perception. Yet, models must be correlated to how humansperceive the world. This study proposes a simple method for suchvalidation. Secondly, in this world of perpetuating standards andever-more sophisticated and easy to use computation platforms,how do novices gain the required intuitive understanding ofmetrics quickly, efficiently and accurately so as to be able toeffectively employ digital tools? By presenting a two-step processof investigation and analysis, pairing participant survey data withdigital analysis, this research attempts to achieve a truly holisticunderstanding of daylight availability metrics. From here, futurelines of research could both deepen the perceptual accuracy ofestablished and emerging daylight availability metrics, as well aslead to similar tests for other metrics such as natural ventilationand thermal performance.

Acknowledgments

The authors are indebted to the Le Corbusier Foundation and theHarvard University Department of Visual and EnvironmentalStudies for letting us use the Carpenter Center for the studentassignment. We also thank Ms. Shelby Doyle for building a detailedRhinoceros model of the Carpenter model. This work has beensupported by the Office for Executive Education at HarvardUniversity Graduate School of Design as well as a Dean’s Grant.

References

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Table 3Comparison of daylight area predictions.

Metric Size of daylitarea [m2]

Difference to studentassessments [%]

Student assessments 163 e

Rule of thumb: 2xWindow-head-height

157 �4%

Daylight factor 122 �25%Sept 21 9 am 151 �7%Sept 21 3 pm 215 þ32%Daylight autonomy [300lux] 152 �7%Useful daylight illuminance

[100luxe2000lux]239 þ46%



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