How light shelves work: (left) In a room with big windows and a light shelf, (1) the light shelf shades the space near the big window from glaring direct light, and reflects indirect (non-glare) daylight into the space to broadly illuminate the room. (2) A light-colored ceiling further improves the reflection of light into the room. (right) Exterior view of example light shelves. Credit: Denise W. Carlson, ITL, University of Colorado Boulder; photo: Lawrence Berkeley National Laboratory

Light Shelves

Light shelves are (sometimes adjustable) reflectors installed on windows on the equator-facing side of a structure. They use a reflective metal or white surface to reflect daylight directly onto the ceiling of an interior space, resulting in a large amount of natural light supplied to the entire space by being dispersed onto the ceiling. A natural light shelf is created in the winter when sunlight is reflected off snow-covered ground and into the structure.

Daylighting examples: (left) Clerestory windows and ample side windows provide excellent lighting and views for a work space. (right) Windows, skylights and door windows help to illuminate a bathroom. (Left: Lawrence Berkeley National Laboratory; Right: Microsoft Corp.)

Clerestory Windows

Clerestory windows are narrow windows located on the upper walls of an interior space. They provide a direct light path to the polar-side and allow for a significant amount of natural light when oriented correctly. On the inside, surrounding the windows with light-colored walls helps to diffuse the light more evenly.

Skylights

A skylight is simply a window cut into the roof of a structure, with a flat, dome- or pyramidal-shaped exterior casing. Skylights admit a great deal of natural light into an interior space, but have some drawbacks, such as heat loss /gain, condensation, and potential for water and ventilation leakage. Care must be taken to address these issues during installation, otherwise the skylight could cost more than it is worth, and thereby decrease overall energy efficiency.

Solar Geometry

Everywhere on the planet, the tilt of the Earth on its axis and your location relative to the equator result in sun paths that change throughout the year. To maximize daylighting, the orientation of the building and position of the sun must be considered when deciding exactly where to place windows. Then, to design any type of system that relies on solar radiation, it is important to take into consideration the seasonal and hourly changes in position of the sun, which directly influence the incident angle of sunlight, and if possible, incorporate a system that can adjust to the position of the sun.

Before Activity

• Gather materials.
• Make copies of the Daylighting Design & TechniqueWorksheet, Solar Azimuth vs. Elevation Plot Handout and Solar Geometry Handout, one each per group.

With the Students

1. Discuss daylighting techniques used in various types of architecture, such as windows, solar tubes, light shelves, clerestory windows and skylights.
2. Explain the importance of solar geometry in designing the daylighting system for the house. Refer to the Solar Azimuth vs. Elevation Plot Handout, as appropriate. Refer to the Solar Geometry Handout for a more detailed explanation.
3. Divide the class into groups of two or three students each.
4. Give each group a worksheet and two handouts.
5. Have the groups follow along with Part 1 of their worksheets to design their model houses.
6. Have students incorporate one or many forms of daylighting into their design (Part 2 on the worksheet).
7. Have students gather all materials as specified in their model house designs.
8. Have students build their designed model house. Refer to the example model house procedure, below.
9. Once teams have finished their models, have each group test their house under the desk lamp, following along and completing Part 4 of the worksheets.
10. Have each group present their model to the class, explaining each type of daylighting used, as well as observations made during testing.
11. Have the groups complete their worksheets.
12. Conclude by leading a class discussion to review the worksheet answers. Incorporate the questions provided in the Assessment section. As time permits (or as a homework assignment), ask students to re-engineer their daylighting system, as described in the Assessment section.

Example Procedure for Building a Model House

1. Cut out a house base according to your scale and design. Scale the model house so that it is ~1,000 sq ft (~93 sq m). Recommended scale: 1 in = 3ft (or ~2 cm = 1m).
2. Measure and cut board pieces for all exterior and interior house walls.
3. Measure and mark windows and other daylighting holes to be cut out of walls, ceilings and roofs. Use the X-Acto knives to cut out all holes (see Figure 1). Be neat in making the window cuts, saving the pieces to make light shelves later.

Figure 1. Cut out daylighting openings for windows in walls (left) and solar tubes in ceilings (right).

4. Cover window openings with packing tape, or other transparent film (see Figure 2).
5. Use hot glue to attach walls to the base of the house (see Figure 2).

Figure 2. (left) Use clear tape to represent glass for window openings. (right) Use hot glue to attach the walls to the model house base.

6. To create a solar tube:: Determine the ceiling member that the tube will extend through. Create the bottom of the tube from a strip of thick paper wrapped in aluminum foil. Curl it and position it in the opening; secure it with hot glue (see Figure 3).

Figure 3. (left) Ceiling with cut-out hole for solar tube. (middle) Solar tube base sized to line the hole with reflective material. (right) Solar tube base installed.

7. Extend the tube to the spot at which you want it to emerge on the exterior of the model (roof), curving as necessary along the way (see Figure 4).

Figure 4. (left) Curve the upper part of the solar tube above the ceiling, through the attic space. (middle) Further extend the solar tube through and above a hole in the roof board. (right) Interior view of the finished solar tube in the ceiling.

8. After placing a roof on the model, cover the exposed top and bottom parts of the tube with packing tape to secure (see Figure 4).
9. To create light shelves: Gather the leftover pieces of foam core board from cutting out the window openings. For each light shelf, cut a piece of plastic drinking straw to the width of its window.
10. Use hot glue to adhere the straw pieces to the bottom edges of the foam core board pieces. Straighten out a paper clip and string it through the straws attached to the light shelves (see Figure 5), making a hinge.

11. Use a glue gun to adhere the paperclip wire holding the light shelves to exterior walls of the desired windows, making sure to allow for rotation of the shelves (see Figure 5).
12. Glue paperclips to the roof, directly above each light shelf/window. Attach a piece of string to each shelf that is long enough to extend beyond the roof paperclips; this permits adjustment of the shelf angle by tightening or loosening the string (see Figure 5).

13. To finish up the model house, close in all sides of the structure except for one, from which to make observations.
14. Use electrical tape to seal up all corners, edges and cracks so light does not leak into the structure (see Figure 6).

Vocabulary/Definitions

• absorption: A process in which the energy of a photon is absorbed by an object, and usually re-emitted as thermal energy.
• artificial light: Light generated from non-renewable energy (usually electricity).
• clerestory window: A daylighting technique. Upper wall windows placed to admit significant amounts of natural light while reflecting and dispersing it throughout the space.
• daylighting: The use of natural light, usually indirect, through the placement of windows, skylights, light shelves, and other techniques to provide internal illumination for a building, and minimize glare and unwanted heat.
• illuminance: The total amount of visible light illuminating a point on a surface from all directions above the surface. Measured in Lux (lx), or lumens per square meter (lm/m2).
• light: Electromagnetic radiation of a wavelength that is visible to the human eye. It is composed of photons. Also called visible light.
• light shelf: A daylighting technique. A horizontal shelf positioned (usually above eye level) to reflect daylight onto the ceiling and shield direct glare from the sky.
• lumen: A very basic unit of measurement for light. If a normal wax candle is positioned at the center of a sphere of 1m radius, then every area of 1m2 on the inside of that sphere receives a luminous flux of about 1lm.
• luminous flux: A measure of perceived power of light, measured in lumens (lm).
• model: (noun) A representation of something for imitation, comparison or analysis, sometimes on a different scale. (verb) To simulate, make or construct something to help visualize or learn about something else (as a product, process or system) that is difficult to directly observed or experimented upon.
• natural light: Light coming directly from a natural source, such as the sun, moon or stars.
• photon: The particle responsible for carrying electromagnetic radiation of all wavelengths (including visible light).
• reflectivity: The fraction of incident light reflected by a surface.
• refraction: A change in direction of a wave due to a change in its speed.
• skylight: A daylighting technique. A roof window that lets in natural light to illuminate a room.
• solar tube: A daylighting technique. A tube or pipe used for pulling daylight through a dome lens, reflecting it through, and then dispersing it in a multitude of angles throughout an interior space. Also called a light tube.
• solstice: Occurs twice a year (winter and summer), when the tilt of the Earth’s axis is oriented directly towards or away from the sun, causing the sun to appear to reach its northernmost and southernmost extremes.
• transmittance: The fraction of incident light at a specified wavelength that passes through a sample.

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.