Description

Background and significance of daylighting

The presence of daylight in educational buildings plays a significant role in the process of learning. Performance of students is measured by a number of yardsticks, among them are students’ performance on tests and level of absenteeism. In the five years between 2000 and 2007, more than 1,000 schools will be built each year in order to meet the demand of students in kindergarten and elementary schools in the United States. With calls for energy conservation, improving the health of children and the quality of the educational settings of kindergartens and schools, some major studies using rigorous scientific methods were undertaken to assess the impact of daylight on the well-being and the scholastic achievements of pupils at all levels. One of such major studies[1] analysed test scores of more than 21,000 students in three school districts in three different US states, namely California, Colorado and Washington. The following results were obtained:

• Students in classrooms with the most daylight progressed 20% faster on math tests and 26% faster in reading tests

• Classrooms with the most window area were associated with a 15-23% faster rate of improvement

• Classrooms with skylights were associated with a 19-20% faster rate of improvement

• Classrooms with operable windows were associated with a 7-8% faster improvement in three out of four cases that have been investigated when compared to classrooms with non-operable windows

Students who attend daylight schools seem to perform up to 14% better than those who do not according to another major survey of 1,200 elementary students in North Carolina. The authors of the study did not provide daylight illuminance levels but they characterised the conditions of the daylight schools as ‘average illumination levels in the skylit classrooms are two or three times higher than in classrooms with electric lighting in peak conditions.’

There seems to be a direct correlation between the presence or lack of daylight and the way pupils perform. But why do students perform better with daylight?

Daylight and circadian rhythm

One of the most obvious relationships between humans and daylight is that of the circadian rhythm, i.e. the cycle of day and night and the complex chemical and physiological variations that control our bodies 24 hours a day. The timing and functions related to these processes depend on our biological clock. Arguably the most influential factor in this timing is the presence of daylight.[2] This rhythm directs the body to release hormones and trigger functions that control our days. Researchers found that from ten o’clock until noon our immediate memory is at its best, and is therefore a positive factor in schoolwork, concentration and debate; whereas the hours from six in the evening to midnight are favourable for studying since then our long term memory is at its best. This circadian rhythm is especially important in children since their systems seem to be more sensitive to change and variation. The presence of daylight in classrooms is crucial to the preservation of this rhythm and the body’s natural clock.

Seasonal Affective Disorder and depression

One possible effect of lack of daylight or lack of the presence of daylight is Seasonal Affective Disorder. Depression, fatigue, irritability and lack of concentration are just a few of the many symptoms that SAD sufferers usually confront. Similar symptoms were found in children confined to windowless classrooms for entire school days. Children exhibited restlessness and much more irritability in these classrooms. Concordantly, children in classrooms with sufficient daylight were able to develop concentration skills with more ease. A by-product of SAD and its symptoms are frequent absences and a lack of resistance towards diseases. Although many of the studies related to SAD have been performed on hospital patients and people in northern latitudes, the results are still relevant to the long term impact on school children.

It has been hypothesised by many studies that melatonin, a hormone which is produced by the pineal gland located in the centre of the brain and is inhibited by light and permitted by darkness. Melatonin may help our bodies know when it‘s time to go to sleep and when it‘s time to wake up. At night melatonin is produced to help our bodies regulate our sleep-wake cycles. Research indicates that it may ameliorate SAD and circadian misalignment. It is believed that it is the key chemical messenger in SAD. It is also widely believed that higher levels of melatonin caused by fewer hours of daylight contribute to SAD. The rate of release of melatonin, like so many other body functions, is controlled by environmental illumination. Melatonin levels in children seem to fluctuate more rapidly than those in adults, and daylight illumination is proven to be of great significance to the health of children.

Daylight and stress

Cortisol, a stress hormone, is also associated with daylight presence indicated by high levels during the day and low levels at night. The release of cortisol is directly related to the body‘s circadian rhythm and is often used as a chronobiological indicator in studies. Cortisol levels are higher in summer and lower in winter.

High levels of cortisol are associated with an inclination towards sociability; medium levels seem to promote concentration and increased focus, according to a Swedish investigation of 90 elementary school students. Both too much and too little cortisol is negative for concentration. A hormone imbalance influences children‘s ability to focus and concentrate, it affects their growth and fosters absenteeism.[3]

Full spectrum lighting which mimics certain spectral characteristics of daylight makes a positive contribution to the learning process in school children according to a Canadian study.[4] Students studying with full spectrum lighting were a lot less absent than those with conventional fluorescent lighting.

It is evident that daylight has a dramatic effect on health both in adults and children. In fact, most of the effects are interrelated and dependant on each other on multiple levels. Melatonin has an inverse relationship to cortisol. SAD is commonly said to be caused by a melatonin deficiency which disturbs the natural sleep-and-wake cycle in humans. Vitamin D deficiency can drastically alter the production of vital nutrients. Meanwhile, our body’s circadian rhythm has control over almost all of these factors and has the ability to drastically affect our system. Most functions overlap and create chain reactions all controlled by daylight. Growth and development are particularly important in children; the amount of time spent in school directly points to the need for these facilities to be designed for their health and well-being. A facility properly designed will have fewer absences and more productive days than one that is ill-fitted for education.

Daylighting strategies for schools and kindergartens

An appropriate daylighting strategy in schools and kindergarten would be one that provides an adequate amount of light where needed while ensuring no visual discomfort and good visual performance. Typologies of school architecture tend to favour single-storey buildings. These are often appropriate for simple yet effective daylighting strategies that include both side-lighting as well as top-lighting principles.

All daylighting systems harvest the daylight available outside and distribute it in a way that optimises the area inside the room. Daylight is comprised of a non-directional diffuse component and a direct component which is directional and dynamic. Fenestrations systems must be sized and placed to account for the dynamic characteristic of daylight. Sunlight, the direct component of daylight, is the most dynamic. It can be harsh, and it can create shadows as well as extreme disparities in illuminance levels inside a room. It can also produce visual discomfort and glare if not controlled properly.

Daylighting systems are of two general categories: 1. top-lighting systems where daylight is distributed inside the room from the ceiling or the roof; 2. side-lighting systems where daylight is distributed from the sides of the room.

Studies have shown that successful daylighting principles are:

• The building should be elongated along an east-west axis. Daylight apertures can be placed on the north side where diffuse daylight is available and the south side where it is relatively easy to control the sunlight in winter and summer.

• Apertures placed high in the wall such as clearstoreys or tall side windows optimise daylight distribution and bring light deeper into the space.

• Bringing daylight from two different directions reduces the chances of discomfort glare and evens out the daylight distribution.

• Use indirect daylighting to control sunlight inside the classroom. Direct sunlight inside a room can cause glare and discomfort.

Side windows

Light levels are much more intense near the window and decrease rapidly as one moves away from the window. The height of the window dictates to a great extent the effective depth of illumination with daylight. Low ceiling and deep classroom could experience a gloomy feeling due to the disparity in light levels between the back of the room and the peripheral area near the window. Effective illumination can be obtained for room depth as much as 2 [1]⁄
_[2]
times the height of the window above the workplane. For example, a classroom with a ceiling height of 3.5 metres and desk height of 0.75 metre, if the top of the window is 2 metres above desk height, the area that is adequately daylit is approximately up to (2 x 2.5 metres) 5 metres deep from the window wall.

Light shelves

When designing with side windows, attention must be given not to create very brightly lit areas near the window and dark ones in the back. Light shelves can provide a good remedy to this problem. They are designed such that the clearstory portion above the light shelf catches sunlight or diffuses daylight and reflects it toward the back of the room away from the window. The protruding portion of the light shelf, in the case of a combined or exterior light shelf, acts as a shading device and prevents sunlight from falling on the work area immediately adjacent to the window. It also cuts on glare and minimises brightness near the window. As a result, more uniform light levels are achieved throughout the room. The clearstory portion of the window may be made of clear glass for maximum daylight harvesting. The lower portion below the shelf is referred to as the view window. The glass in it may be tinted to reduce glare.

Skylights

Skylights are another top-lighting strategy used for single-storey schools to bring daylight from the top rather than the side. The drawing indicates the recommended spacing between skylights as function of the mounting height of the skylight, or the distance between the bottom of the skylight and the workplane. The depth of the skylight well, the size of the opening of the skylight dictates largely the efficiency of the skylight system. A very large portion (up to 75% or even more) of the luminous energy incident on the outside of the skylight may be lost within the skylight if the skylight well is too deep or too dark.

A single skylight could create large disparity in light levels between the area underneath the skylight and the rest of the room. The size of the skylight opening also dictates the daylight distribution. More than one skylight will help balance daylight inside the space.

Clearstory windows

Clearstory windows admit light deep towards the back of the room and henceforth create a more uniform daylight distribution throughout if there is another side window. The relationship between illumination from side window and clearstory depends on size, height and position. With typical narrow window arrangements for clearstories, the recommended depth from the plane of the clearstory to the opposite wall is about equal to the distance from the mounting height of the clearstory above the workplane level. For wider clearstories the depth could be one and half the mounting height. To obtain adequate and more uniform daylight distribution, the height of the clearstory window should be about one half the side wall window height. Not only the height of the clearstory affects the depth of the daylight penetration but also the width of the clearstory window.

Sawtooth systems

Sawtooth systems are an excellent daylighting strategy when uniform daylight distribution is desired throughout a large classroom or work surface. There is directionality in light distribution under these systems especially on clear days and if the opening is facing south. On an overcast day, however, sawtooth systems provide a little more uniformity than on clear days. In general daylight levels are higher towards the end of the room that faces the opening. The spacing between sawteeth is recommended to be 2 1⁄2 H, with (H) being the height of the ceiling clearance.

Roof monitors

Like the sawtooth system, a roof monitor is also an excellent daylighting strategy when uniform daylight distribution is desired throughout a large classroom or work surface. Roof monitors bring in light from above from two opposite directions. Henceforth directionality of light is minimised and uniformity is maximised. Roof monitors can be designed to allow sunlight in winter if desired and block it in the summer when not desired.

Anidolic systems

Anidolic systems collect sunlight falling on an entry aperture and concentrate it on a smaller exit aperture where the receiver is placed. The receiver is a light emitting source or a highly efficient luminaire capable of controlling beam output through well-defined beam spread.

The protruding portion of the system acts as a solar collector and concentrator. It collects large amounts of sunlight through the entry aperture and concentrates it onto a smaller area where the diffuser or distributor is located near the exit aperture. The distributor spreads daylight over a larger area further away from the side wall window.

Recommendations for visual comfort

Visual tasks occurring in schools range from very small to very large and from simple to complex. There are tasks that may require prolonged periods of concentration and others very brief ones. Minimum recommended illuminance levels for various tasks taking place in a school environment are displayed in the below table according to data from the American National Standard Guide for School Lighting (ANSI/IES RP-3, 1977).

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Originally published in: Mark Dudek, Schools and Kindergartens: A Design Manual, Birkhäuser, 2015.