LIGHT SHELVES are used to distribute more evenly the daylight entering a buidlding typically through

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Light Shelves
LIGHT SHELVES are used to distribute more evenly
the daylight entering a buidlding (typically
through a sidelighting aperture). The
distribution of the daylight depends on the form,
material and position of the light shelf. The
light shelf can be positioned inside, outside or
in both positions. The defining element is that
there is glazing directly above the plane of the
shelf. The exterior light shelf can act also as a
shading element.
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Light Shelves
INTENT More even and somewhat deeper
distribution of daylight, reduction of glare
potential. EFFECT Reduces consumption of
electricity, potentially reduced cooling loads.
OPTIONS Exterior, interior, or continuous
shelves, fixed or adjustable. COORDINATION
ISSUES Ceiling design, daylighting aperture,
glazing, internal partitions, orientation,
shading, heat gain. RELATED STRATEGIES Daylight
Factor, Internal Reflectances, Shading
Devices. LEED LINKS Energy Atmosphere, Indoor
Environmental Quality PREREQUISITES Preliminary
room design (geometry), information on room
orientation, site latitude, sun angles, site
obstructions.
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Light Shelves Implementation Considerations

• ORIENTATION Light shelves can be effective
  shading devices on south-facing facades in the
  northern hemisphere. Light shelved capture
  additional solar radiation and can therefore
  contribute to additional cooling load.
• SHELF HEIGHT AND ANGLE Should be placed above
  eye level to avoid glare. Horizontal shelves are
  most common because they provide balanced
  distribution, glare control, shading performance,
  and aesthetic potential. Tilted light shelves
  however can provide better performance.
• CEILING A high ceiling is desirable. If
  floor-to-floor height is low, tilting the ceiling
  towards the window aperture is a useful way of
  improving the light distribution.
• WINDOWS Higher windows allow light to penetrate
  deeper. Clear double-paned glazing is recommended
  for windows above the shelf for most climates.
• SHADING Use horizontal blinds for the window
  above the shelf.
• MAINTENANCE Consider how the shelves can be
  maintained since debris reduces the reflectivity
  of the shelf. Consider rain runoff and snow
  collection for external shelves.
• DIMENSIONS The top surface of light shelves
  should be at least 2ft from the ceiling. The
  ceiling height should be at least 9ft.

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Light Shelves Further Readings
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Internal Relfectances
INTERNAL REFLECTANCES of a space are governed by
two primary surface characteristics of the
building materials COLOR AND TEXTURE. Color
determines the quantity of light reflected by a
surface. Dark-colored materials absorb light
while light-color materials reflect light.
Texture determines the quality of light leaving
the surface after the reflection. Rough textured
surfaces, referred to as matte, create diffused
reflected light. Smooth or glossy surfaces create
specular reflected light. When lighting a space,
diffuse light is preferable because specular
surfaces can lead to glare. A larger space has
more opportunity for interreflections (losses)
than a smaller space (both in section and plane)
since the further away from the light source the
more light will be lost en route via
interreflections.
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Ambient light is the general light that
illuminates the entire scene. It has a uniform
intensity and is uniformly diffuse. It has no
discernible source and no discernible direction.
By default, there's a small amount of ambient
light in every scene. If you examine the darkest
shadows on your model with the default ambient
light setting, you can still make out the surface
because it's lit by the ambient light. Shadows in
your scene will not appear any darker than the
ambient light color, which is why you usually
keep ambient light set to black (or a very dark
color).
Diffuse color is the color that an object
reflects when illuminated by "good lighting,"
that is, by direct daylight or artificial light
that makes the object easy to see. When we
describe an object's color in conversation, we
usually mean its diffuse color. The choice of an
ambient color depends on the kind of lighting
for moderate indoor lighting it can be a darker
shade of the diffuse color, but for bright indoor
lighting and for daylight, it should be the
complement of the primary (key) light source. The
specular color should be either the same color as
the key light source, or a high-value
low-saturation version of the diffuse color.
Specular color is the color of highlights on a
shiny surface. The highlights are reflections of
the lights that illuminate the surface. For a
naturalistic effect, set the specular color to
the same color as the key light source, or make
it a high-value, low-saturation version of the
diffuse color.
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Internal Reflectances
INTENT Optimized lighting effectiveness EFFECT
Energy efficiency, visual comfort OPTIONS
Numerous materials, finishes, and reflectances.
COORDINATION ISSUES Clients preferred finish
materials and colors, tasks related to the space,
visual comfort, furnishings, windows, electric
lighting. RELATED STRATEGIES Toplighting,
Sidelighting, Daylight Factor, Light
Shelves. LEED LINKS Energy Atmosphere, Indoor
Environmental Quality PREREQUISITES This
strategy is essentially a prerequisite for
successful daylighting.
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Internal Reflectances Design Considerations

• Make sure the window jamb and sill have a high
  reflectance since they can make excellent
  reflectors. Splay deep jambs away from the
  window.
• Ceiling is the most important surface for
  daylighting. Choose paint and color with 90
  reflectance to optimize distribution of light.
  (see tables in the next slide_
• Angling the ceiling towards the source of
  incoming light can increase the amount of
  reflected light. This works well especially for
  light coming from the clerestory windows.
• Assume that the angle of reflection is the same
  as the incidence angle of incoming light to
  simplify design decisions regarding the placement
  of surfaces.

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Internal Reflectances Further Readings
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Shading Devices
SHADING DEVICES can significantly reduce building
heat gains from solar radiation while maintaining
opportunities for daylighting, views, and natural
ventilation. Conversely, careful design of
shading can admit solar gain during times of the
year when such energy is desired to passively
heat the building. While the focus of shading are
often windows and skylights, walls and roofs can
also be shaded to help reduce the heat gain.
Radiation is an energy transfer form that does
not require a material medium through which to
travel. Solar heat gain coefficient SHGC is a
dimensionless number (0 1) that indicates how
much of solar radiation is passing through a
material. Shading coefficient SC is defined as
the ratio of radiant heat flow through a
particular window relative to the radiant heat
flow through 1/8 thick double-pane clear window
glass. Shading coefficient applies only to
fenestrations. SHADING DEVICES if places inside
can reduce the heat gain up to 20, however,
placing it outside can reduce the heat gain up to
80. The preferred hierarchy for placing shading
is external to the glazing, integral with the
glazing, and then internal to the glazing.
Knowing the sun path at different times of the
day, month, year allow designers to provide
shading when is desirable. Some shading devices
use movable and adjustable parts.
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Shading Devices Key Architectural Issues And
Implementation Considerations
The massing and orientation of the building are
key for determining a building that can be easily
shaded. East and West are difficult to shade due
to the low angle of the sun. A building with long
north and south façade and short east and west is
usually easier to shade. Reflective surfaces on
top side of horizontally placed shading devices
can reflect light into the building and improve
the daylighting conditions.
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Shading Devices Design Procedure

• Determine the shading requirements. They are
  specific to the buiding, spaces inside the
  building, and many other variables including
  climate, building envelope design, visual comfort
  expectations, and thermal comfort expectation.
• Determine whether the shading will be exterior,
  integral or internal.
• Develop a trial design for the shading device.
• Check the performance of the shading device using
  shading masks and scale models.
• Modify shading device until the desired
  performance is obtained.

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Shading Devices
INTENT Energy efficiency through screening solar
radiation and allowing it when needed. EFFECT
Reduced cooling load, solar access when desired,
reduced glare. OPTIONS Devices internal,
integral or external to the building envelope,
movable or fixed. COORDINATION ISSUES Building
orientation and footprint, passive and active
heating and cooling, natural ventilation. RELATED
STRATEGIES Toplighting, Sidelighting, Cross
Ventilation, Direct Gain, Indirect Gain. LEED
LINKS Energy Atmosphere, Indoor Environmental
Quality PREREQUISITES Site latitude, window/wall
orientation, skylight tilt/orientation, massing
of neighboring buildings and trees, a sense of
buildings heating and cooling loads.
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