The dilemma of classroom lighting design in the built environment presents itself with considerable faults and insufficiency. By reason, classrooms should be made to host dynamic, light infused atmospheres, that contribute to the bettering of students’ overall wellbeing and learning experience. The problem in the latter, is that lighting design is rarely tailored for a given context, and metrics of lighting analysis are not sufficiently utilised to configure lighting strategies that employ fruitful learning. This purpose of this report is to investigate and strategize the application of daylight and electric lighting in a given classroom to better learning.
Ambient Lighting –
Correlated Colour Temperature (CCT) – -
Colour Rendering Index (CRI) –
Daylight Factor –
Glare –
Illuminance –
Luminance –
Luminous Flux –
Spatial Daylight Autonomy (sDA) -
Building with lighting that directs for conducive health and wellbeing, bestows occupants the opportunity to benefit on multiple fronts. Even with minimal awareness on the ever-emerging studies that uncover lighting’s contributions towards elated behaviour and cognition, performance and alertness, mood, and stimulation, or even all the above – one cannot deny that light has long been generous and vast in human nourishment and evolution – extending beyond its aid in mere comfort and the capability to see.
It is of no question that light and human beings have a very interesting relationship with one another, and to state that one lighting design strategy exists for the diverse requirements of a learning environment, would mean to neglect learners as multi-faceted individuals with differences that drive certain behaviours and needs, and to neglect light as a module of dynamic and varying conditions. Accordingly, lighting design can be categorised as follows: daylighting, electric lighting, and integrated daylight and electric lighting. By reason, each of these lighting conditions urges classrooms to host dynamic, light infused atmospheres, that contribute to the bettering of students’ overall wellbeing and learning experience. The problem in the latter, is that lighting design rarely extends beyond guidance or regulation compliance – and a challenge further lies within tailoring a lighting design strategy that harmonises both, lighting metrics and the given context altogether.
Daylighting for instance, as raised by CIBSE, presents itself most effective when the architectural form and the associated shading system serve to temper the luminous environment. That is, through providing adequate levels of daylight whilst simultaneously blocking out unwanted levels of direct sunlight of which can cause visual comfort issues, such as uneven light distribution and glare. In cases where lighting design is not considered a sensory principle, classrooms can present themselves with all types of inefficiency and defect that deny both student and teacher, a fruitful learning sphere. WELL (2020) propose that pairing adjustable direct task lighting with indirect or diffuse ambient lighting allows user customization and good visual acuity while providing suitable background light. It is however important that individuals are not simply situated within a well-lit room, but rather they are offered adaptable light that adheres to the variety of activities and teaching techniques carried out, and that it is fair to students wherever they may be seated.
In order to form a strategy that explores and employs such account of lighting, it is important to first refer to a specified context – Figure 1.1 presents a plan and section of a classroom that will serve the analysis of lighting metrics, as well as inform what would be required in terms of lighting design to sustain conducive wellbeing, performance, and comfort for 11–18-year-olds in a learning environment. It is assumed that the tasks carried out within the space will expand on reading, writing, group discussions and presentations - and will be carried out within a typical school learning period of 08:00 to 15:00.
As location further occupies a key role in underpinning the wider population’s cultural and environmental reactions to light, the classroom will theoretically reside in Alexandria, Egypt (31.2001° N, 29.9187° E) and in its efforts, regard a unique conception of lighting.
Ultimately, an adequate lighting strategy should make maximum use of daylight - and in doing so, student’s circadian system is not disturbed by improper ‘time-cues’ of in-sufficient light, their behaviour and cognition is subjected to improve, and the chances in yielding a good learning environment with positive influence on mood and stimulation are increased (Hobday, 2006; Knez & Kers, 2000; van Bommel & van den Beld, 2004). The CIBSE Guide A (2015) quantifies a daylit environment by stating “If the average daylight factor exceeds 5% on the horizontal plane, an interior will look cheerfully daylit, even in the absence of sunlight. If the average daylight factor is less than 2% the interior will not be perceived as well daylit and electric lighting may need to be in constant use.”
Now, it is important to recognise that the average daylight factor is a valuable metric for daylight only when spaces are situated under an overcast sky. In terms of using this method, which is adopted diligently by guidance and standards in quantifying daylight provision, to assess adequate daylight levels within spaces located under predominant clear skies such as Alexandria, there rises difficulties. One of which, is estimating the variability of external light incident on a window wall, where incoming daylight from clear skies is considered a product of skylight and externally reflected sunlight – a component that is further difficult to estimate due to the function of several variables altogether. Under overcast skies, daylight is assumed to diffuse within the interior space evenly and from such, a simple value is derived. Alshaibani (1997), proposes a solution for predicting internal illuminance under clear skies – by first assuming that the internal surface of the internal window is a perfect diffuser, the angle of incidence of external light is assumed insignificant, and hence external illuminance can be dealt with as one quantity. Second, the external illuminance on the window plane is equal to the horizontal diffuse illuminance. This is worked out and fed in conjunction with contributing factors to present an equation for the average daylight factor under clear skies (presented in figure 1.2). While it is implicit to understand this, this report will continue to adopt the average daylight factor as a reasonable lighting metric in assessing the performance of daylight within a space, as this allows comparisons to relevant guidance and standards.
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Alternatively, LEED (2021) set an sDA target for the occupied area of at least 40%, medium of 55% and best at 75%. Similarly, WELL (2020) recognise an sDA (300 lux/ 50%) achieved for at least 55% of the regularly occupied space as a sufficient application of daylight. Table 1.1 illustrates recommendations and targets of daylight factor values and illuminance levels based on the reviewed standards and guidance, while table 1.2 combines all findings to inform a practical brief appropriate and potentially applicable to the classroom in Alexandria, Egypt with rationale behind the selection of metrics.
Essentially, indicating the division of areas with a direct view of the sky to those without, informs the extent to which daylight can be perceived as present in a space. A way to explore this can be through the use of the ‘No-Sky Line’ tool. Using the section of the given classroom, a line has been drawn from the working plane grazing the head of the window to the external obstruction, as illustrated in figure 2.1. As the point in which the sky component is zero, extends to the rear of the classroom, it is assumed that daylight within the space will prove to be more sufficient than not, it will visually appear even, and its distribution will not be heavily reliant on reflecting surfaces.
Using the average daylight factor to further analyse daylight in the room is an effective way to understand its relationship in overcast sky to design parameters. In light of this, the potential performance of the classroom is investigated in terms of variable parameters as shown in table 2.1 - where the glazing area of the windows and the total area of enclosing surfaces have been obtained from the classroom’s design specifications, other contributors have assumed values – these are highlighted in red. It is important to note that among the investigated parameters is the angle of visible sky, this is due to likelihood of the exterior environment to change over time – aspects such as new builds in the surrounding area, extensions within existing ones, or even prolonged scaffolding on the façade, all need to be considered in order to undertake a practical lighting analysis.
AVERAGE DAYLIGHT FACTOR CALCULATION
VARIABLE PARAMETERS
AVERAGE DAYLIGHT FACTOR (%)
VISIBLE SKY ANGLE (Ø) 2.5 2.7 2.9 3.2 3.4
GLASS TRANSMITTANCE (T) 2.1 2.5 2.9 3.4 3.8
AVERAGE REFLECTANCE OF ROOM SURFACES (R) 2.2 2.5 2.9 3.7 5.2
From this, it is evident that average daylight factor results with a likely compliance to the proposed brief demonstrated in stage 1, would require a visible angle value greater than 60 and/or a glass transmittance value greater than 0.7, and/or an average surface reflectance greater than 0.6. Considering that the formula can further be transposed to give the glazing transmittance required to achieve a specific average daylight factor, this is investigated in table 2.2 and 2.3, with alterations to the surface reflectance and the angle of visible sky calculated as seen in figure 2.2. A desirable scenario of an average daylight factor of 4 presents itself, where R=0.7 and T=0.7.
GLASS TRANSMITTANCE CALCULATION
AVERAGE
GLASS TRANSMITTANCE (T) 2 0.45 3 0.65 4 0.90 - (impractical) 5 1.10 - (N/A)
DAYLIGHT FACTOR (%)
As the previous approaches do not however consider sunlight, the sun path in Alexandria and its assumed solar penetration on the classroom during the school period is demonstrated in figure 2.3. In favour with the target brief composed in stage 1, the altitude of the sun due to its geographical location along with the often-clear skies of Alexandria, make it more possible to achieve high illuminance levels within 75% of the occupied space. On the other hand, it is notable that depending on the orientation, overheating, glare, and visual discomfort may become an issue due to excessive solar penetration. While this will later be investigated in the next stage of this report, figure 2.4 presents an illustration that expands on how orientation occupies a key role in limiting the access of direct sunlight indoors.
JUNE SUN SEPT. SUN JAN. SUN
WINDOWS FACING EAST
WINDOWS FACING SOUTH EAST
As demonstrated earlier, Alexandria experiences predominantly sunny weathers, and hence much of the daylight inside the classroom is a product of skylight, externally reflected sunlight, and direct sunlight. While this may present significant levels of daylight internally, it advances with concerning qualities of visual and physical disruptions, and consequently interfering with the quality of the learning environment. A good lighting design strategy would want to avoid the application and use of blinds that ultimately blocks out outdoor diffuse light simultaneously with direct light - further resulting in electric lighting to more heavily be relied on. In the stage of the report, the sample classroom will be tested in several daylight simulation scenarios, in its efforts to uncover the sensitivity between choices involved in lighting design and progress an optimal configuration of lighting metrics in relation to the way of the sun in Alexandria.
An appropriate starting point would be to explore the photometric values of an average daylight factor of 3% as targeted by the brief, and lightly investigated in tables 2.2 & 2.3 in stage 2, to the software simulation. As this will be simulated under an overcast sky, it is recognised that derived values will be unfair to the precepted environment. Nevertheless, assuming that the external light incident on the wall is balanced out by the underestimation, the average daylight factor can be regarded as an estimate. Results are shown in table 3.1.
SIMULATION (1)
BASELINE - AV.DF
ROOM & LOCATION PARAMETERS SAME? ASSESSMENT METRIC
- DIMENSIONS X
- PHOTOMETRIC VALUES X
- FENESTRATION X
- SITE SETTING X
- EXTERNAL SHADING X - WEATHER DATA X
SIMULATION 1(A)
SIMULATION 1(B)
values of simulations 1(A) & 1(B))
PHOTOMETRIC VARIABLE VALUE OUTPUT ASSESSMENT
Floor reflectance 0.5 Wall reflectance 0.6 0.7 0.2 Glass transmittance 0.65 = 2.7 %
PHOTOMETRIC VARIABLE VALUE OUTPUT ASSESSMENT
Floor reflectance 0.4 Wall reflectance 0.5 0.6 0.2 Glass transmittance 0.7 = 2.5 %
SIMULATION (2)
While the average daylight factor falls slighting under the 3% mark, by using the same photometric values in simulation 1(A) to assess the spatial daylight autonomy (300lux/50%), the appropriate orientation of the classroom can be revealed. The daylight factor obtained can hence be sufficient if the sensory environment has plausible adequacy. This is explored in table 3.2, 3.3, and 3.4 respectively.
NORTH sDA
-
ROOM & LOCATION PARAMETERS SAME? ASSESSING
- DIMENSIONS
- PHOTOMETRIC VALUES
- FENESTRATION
- SITE SETTING no
of simulation)
- EXTERNAL SHADING X OUTPUT ASSESSMENT
- WEATHER DATA sDA = 60.9 %
SUPPORTING
IMAGE
SIMULATION (3)
EAST sDA SUPPORTING IMAGE
-
ROOM & LOCATION PARAMETERS SAME? ASSESSING
- DIMENSIONS
- PHOTOMETRIC VALUES
- FENESTRATION
- SITE SETTING no
of simulation)
- EXTERNAL SHADING X OUTPUT ASSESSMENT
- WEATHER DATA sDA = 74.1 %
SIMULATION (4)
SOUTH-EAST sDA
ROOM & LOCATION PARAMETERS SAME? ASSESSING
- DIMENSIONS
- PHOTOMETRIC VALUES
- FENESTRATION
- SITE SETTING no
of simulation)
- EXTERNAL SHADING X OUTPUT ASSESSMENT
- WEATHER DATA sDA = 81.0 %
SUPPORTING IMAGE
As the South-East orientation best fits the targets set out in the brief in stage 1, and further corresponds with LEED’s (2021) 3-point credit of a 75% sDA, the classroom will there forth be oriented accordingly. There is a high probability however, that these results might be a product of solar penetration as direct sunlight was included in the sDA simulation. In efforts of mitigating this for health and comfort purposes, the following simulation proceeds to explore the placement of horizontal shades on the exterior of the windows – results are portrayed in table 3.5.
SIMULATION (5) ROOM & LOCATION PARAMETERS SAME? ASSESSING
- DIMENSIONS
EAST sDA+SHADING SUPPORTING IMAGES
SECTION
- PHOTOMETRIC VALUES
- FENESTRATION
- SITE SETTING
- EXTERNAL SHADING X OUTPUT ASSESSMENT
- WEATHER DATA sDA = 48.1 %
of simulation) MITIGATION OF SOLAR PENETRATION
Through the newly derived sDA value, it is evident that when the sun is assumed to present excessive levels of direct solar penetration, the overhang mitigates this by diffusing direct sunlight upwards onto the ceiling – simultaneously bringing brightness into the classroom. It is important to note that here the sun light is not fully blocked, but rather some of it is reflected off the shading overhang to avoid direct solar penetration onto the working plane.
By uncovering the potential opportunities of simulation modelling in achieving adequate daylight in the classroom, a trade-off has been made between achieving the set sDA target and providing students with a comfortable learning environment. Further changes to better this trade-off would be to introduce mechanical controls the horizontal overhang – from such, users can operate and employ the shading strategy when they deem it fit.
As the final simulation (No. 5 – ‘EAST sDA+SHADING’) tends most to successfully fulfilling the target brief, the report will proceed in informing an appropriate electric lighting strategy whilst referring to the set configuration.
The principle of ‘good combined lighting’, holds the capacity to promote most of the psychological benefits of that found from daylight. This approach of lighting design, also referred to as ‘permanent supplementary artificial lighting of interiors’ is based on the concept of providing illumination that appears to be of good daylight character, even in cases where most of the working illumination might be supplied by unobtrusive electric light sources (McMullan, 2007). This strategy considers three component parts: the distribution of light, the choice of lamps, and the switching control system. It brings up the principle of how electric lighting should be designed to complement daylight - and acknowledges the sensory perception of the lighting quality accordingly.
Essentially, the distribution of electric light would appear to mimic daylight – this can be achieved through the positions of the control switches, and by the organisation of the lighting circuits in relation to the daylight distribution. In a sense, illuminance would gradually increase towards the windows, and the light intensity from both sources would not vary drastically, with sudden changes of illuminance between the room’s surfaces kept to minimal. Ultimately this requires the electric lighting to present itself with a CCT value in the range of 4000-6500K, and a neutral interior colour scheme to uphold the same appearance under both natural and artificial light. The switching controls are to further control the electric lighting with photoelectric cells, in which the electric lighting system will switch on and off according to the changing daylight – this has the added benefit of reducing energy consumption. Tubular florescent lamps are to be used and recessed in the ceiling. This is to avoid its fixture from opposing potential light reflectance on the ceiling caused by direct sunlight from the overhang, but rather merge harmoniously with it.
In adopting this approach, it is recognised that a combined lighting system that gives only a uniform horizontal plane illuminance will not be sufficient in enhancing the overall lighting quality of the indoor environment. It is further necessary to consider the how the electric lighting will create the sensation of brightness in areas distant from the existing windows. While the daylight strategy already utilises the external shading overhang to disperse direct sunlight, the same needs to be carried out with the electrical lighting in areas remote from the windows.
Excessively bright, potentially glaring spots and large variations of light intensity within different areas of the classroom, however, are to be avoided in order to prevent visual stress and discomfort. On the other hand, incorporating a sense of variation on surfaces, will enhance the sensation of brightness. For this, Lumen Pulse’s 4000K ‘wide-flood’ Lumenline surface wall mount is proposed as a suitable fixture (see appendix 6 for specifications).
An illustration on how this electric lighting strategy can be imple-
It is of no question that light is in constant change and activity. Its graceful fluidity into built spheres and the exterior environment make it all the more difficult to analyse, measure and skilfully employ in design strategies. It is with reason, that metrics involved in lighting analysis are approached as interdependent components with dynamic facets. Because lighting profoundly affects numerous human attributes, such as cognitive performance, attention, concentration, and behaviour along with other health factors such as vision, circadian rhythm, and mood, it is implicit to direct attention towards its effects on learning spaces and leaners.
Although there may yet remain a research gap on the numerous variables that contribute to or deduct from the overall learning experience, the objective effort of this report was to situate an informed knowledge on the behaviour of lighting within a given space and in doing so, can lighting be optimised to best suit wellbeing and comfort in a specified context.
By analysing the classroom’s performance in terms of daylight, it became evident that vast consideration needed to be directed more towards preventing issues of physical and visual discomfort rather than merely enhancing health and wellbeing. For the classroom to present an adequate and appropriate lighting strategy in an environment where the sun is predominantly at high altitudes and in accommodation of clear skies, a substantial approach of assessment needed to be adopted. In the scenario of designing for natural lighting under clear skies for instance, the availability of simple prediction techniques were lacking - this might have given assumed results a slight misconception. Nevertheless, the adopted technique of simulation modelling aided the process of understanding the role of different configurations on lighting parameters, and consequently informed strategies applicable to scenarios liable for improvement such as mitigating solar penetration via the use of a horizontal overhang whilst simultaneously maintaining an adequate daylight penetration. Such scenarios on the classroom’s predicted performance, with the applied techniques and metrics, later fed towards employing an electrical lighting design strategy that compliments the overall subject matter rather than oppose it – all of which made it more probable in achieving the proposed target brief.
While there is yet room for improvement in terms of assessing these proposed strategies with regard to exact and true lighting levels from both daylight and electric lighting, the average daylight factor and spatial daylight autonomy proved to be sufficient in objectifying targets and employing strategies for practical implementation. Surely, a rigorous and thorough lighting design proposal for classrooms can enhance learning through the account of such metrics.
