Chapter 6
Directional Effects of Lighting
1
Directional Effects
• Intensity and direction
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An object’s appearance
Architectural features
Ability to perform a task
Quantity of illumination
• Layered lighting plans
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Brightness and Glare
• At source of light
• At destination of light
• From different angles
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Chapter 3
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Directional Effects of
Controlling Brightness
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Subjective responses
Context of the situation
Personal vision attributes
Light sources
Directional qualities
Simultaneous contrast
Characteristics of elements of the design
Glare
• Contrast between two areas is severe
(greater than 3:1)
• Glare can cause:
– A loss in visual acuity
– Eye fatigue and strain
Glare-ing situations
• Settings that require contrast for
effective visibility and attention
• Task lighting
Direct Glare
• Examples:
– Sunlight
– Unshielded incandescent lamp greater
than 25 watts
– Unshielded downlights
– Variation in lighting level in adjacent
spaces
Indirect Glare
– Light source reflected from a light color or
a shiny surface
– Specular materials (called veiling
reflections):
• Glass
• Mirrors
• VDT screens
• High-gloss surfaces, such as a highly polished
wood
Controlling Glare
– Locate luminaires out of field-of-vision
– Use lower-brightness luminaires (linear
source, not point source)
– Choose smaller apertures
– Shield light source with baffles and lenses
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Eye’s Field of Vision
• Central field of vision:
– ~2 degrees above and below the direct line of sight
– Visual acuity (ability to see detail) is best in this range
central field of vision
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Visual Comfort
…increase the visible surface area
of the source
…redirect the light straight down
…block light with a baffle
Lamp choice
• R, PAR and MR lamps
• Non-specular reflectors, baffles
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Chapter18
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Directional Effects of
Controlling Light
• Refraction:
– Example: Light passing through a prism
• Direction of a light source altered to
maximize amount of light falling on a
surface:
– Example: Prismatic lenses from glass or plastic.
Prisms refract light to the space and reduce glare
• Glass and plastic lenses without prisms
distribute illumination through diffusion or
transmission
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Chapter19
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Directional Effects of
Controlling Light
• Transmission:
– Allows incident light to pass through
• Direct:
– Majority of light passes through material
• Mixed:
– Most light passes through in a semiscattered matter
• Diffused:
– Light scattered in many directions
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Chapter20
6
Directional Effects of
Illumination Zones: task
oriented
– Immediate task
– Area
surrounding the
task
– Background
zone 3
zone 2
zone 1
23
Reflectance and Texture
• Specular reflection: Results when
incident light is reflected
• Semi-specular reflection (etched
glass): Most of the incident light is
reflected
• Diffused reflection: Incident light
Chapter24
6
2006
scattered©Publications,
in
aFairchild
variety
of
angles
Directional Effects of
Inc.
Reflectance
• The ratio of incident lighting to the light
reflected from a surface or material
• Expressed as a percentage
• Environmental factors that affect
reflectance values in a space:
– Size of the room
– Location of a surface
– Light sources
Incident and Reflectance
• Angle of incident and reflectance
angle of incident
angle of reflection
Chapter 6
Directional
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Publications, Inc.
26
Reflectance Effects of
Texture
• Light is reflected or absorbed:
– Smooth and shiny materials reflect more light
than rough and heavily textured materials
• Specular reflection: Results when incident
light is reflected
• Semi-specular reflection (etched glass):
Most of the incident light is reflected
• Diffused reflection: Incident light scattered in
a variety of angles
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Chapter27
6
Directional Effects of
Lighting Conditions
100%
30%
30%
Controlling Light
• Some lamps designed for optical
control:
– R, PAR and MR lamps
• Elements of luminaires designed to
control illumination:
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Shielding devices
Reflection
Refraction
Diffusion
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Chapter29
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Directional Effects of
Controlling Light
• Reflection in luminaires:
– Shiny aluminum on inside surfaces
– Reflector contours:
• Spherical
• Parabolas
• Ellipses
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Chapter30
6
Directional Effects of
Controlling Light
and Accent Lighting
• Patterns of light and shadow can
reinforce elements of interior
architecture and objects of emphasis
• Required for accent lighting:
– Select what should be highlighted
– Select which objects or areas should be
hidden by shade and shadow
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Chapter31
6
Directional Effects of
Patterns of Light Shade
and Shadow
• Shape and length of shadows
dependent upon:
– Intensity of a light source
– Angle of direction
– Distance from object
• High intensity/close to object:
– Dark shadow with defined details
• Light sources at a low angle:
– Elongated shadows
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Chapter32
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Directional Effects of
Lighting Objects
Twodimensional
objects
Translucent materials
• Glass and other non-opaque materials
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Transparent
Semi-opaque
Fritted or frosted
Internal materials
Colors
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Chapter40
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Directional Effects of
3-form
Architecture
Elements
Patterns of Light
• Objects appear attractive by positioning a
light source to the side at 15-45 degrees
• Shiny materials: Light source at side of
object
• Glass objects: Illuminated from above and
below
• Pinhole opening < 30 degrees angle of
beam enhances form, textures, and shapes
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Chapter44
6
Directional Effects of
Luminaires