chapter 6 directional effects of lighting 1. © 2006 fairchild publications, inc. directional...
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Chapter 6
Directional Effects of Lighting
1
© 2006 Fairchild Publications, Inc.
Directional Effects
• Intensity and direction– 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
Controlling Brightness– 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
© 2006 Fairchild Publications, Inc.
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
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
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central field of vision
Visual Comfort
…increase the visible surface area of the source
…redirect the light straight down
…block light with a baffle
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Lamp choice
• R, PAR and MR lamps• Non-specular reflectors, baffles
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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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Controlling Light• Transmission:
– Allows incident light to pass through• Direct:
– Majority of light passes through material • Mixed:
– Most light passes through in a semi-scattered matter
• Diffused:– Light scattered in many directions
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Illumination Zones: task oriented
– Immediate task– Area
surrounding the task
– Background
zone 3
zone 1zone 2
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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 scattered in a variety of angles
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
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Incident and Reflectance
• Angle of incident and reflectance
angle of incident
angle of reflection
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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
Lighting Conditions
100%
30% 30%
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Controlling Light• Some lamps designed for optical control: – R, PAR and MR lamps
• Elements of luminaires designed to control illumination:– Shielding devices– Reflection– Refraction– Diffusion
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Controlling Light
• Reflection in luminaires: – Shiny aluminum on inside surfaces– Reflector contours:
• Spherical• Parabolas• Ellipses
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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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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
Lighting Objects
Two-dimensional objects
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Translucent materials
• Glass and other non-opaque materials– Transparent– Semi-opaque– Fritted or frosted– Internal materials– Colors
3-form
Architecture
Elements
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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
Luminaires