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LIGHT SOURCE AND FIXTURE SELECTION The
lighting design process in its most basic form entails
identifying a task and then providing a light source
that will provide proper quantity and quality of light
for the task. The fixture protects the light source,
connects it to the power source and distributes its
light. In this article, we will review the basic factors
that go into specifying a light source and a fixture.
Light
Source Specification Checklist
The light source is the actual light-producing
component of the lighting system. It may operate
simply as a lamp (incandescent/halogen) or as
a lamp powered by a ballast (fluorescent and
high-intensity discharge [HID]).
Below are considerations for specifying three
basic lamp types:
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Incandescent
Lamps |
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Do not require a ballast |
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Warm color appearance with a low color temperature
and excellent color rendering (CRI 100) |
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Compact light source |
· |
Simple maintenance due to screw-in Edison base
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Less efficacious light source |
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Filament is sensitive to vibrations and jarring
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Bulb can get very hot during operation |
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Must be properly shielded because incandescent
lamps can produce direct glare as a point source
|
· |
Require proper line voltage as line voltage
variations can severely affect light output
and service life
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Fluorescent
Lamps |
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Require a ballast |
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Range of color temperatures and color rendering
capabilities |
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Low surface brightness compared to point sources |
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Cooler operation |
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More efficacious compared to incandescent |
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Ambient temperatures and convection currents
can affect light output and life |
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All fixtures installed indoors must use a Class
P ballast that disconnects the ballast in the
event it begins to overheat; high ballast operating
temperatures can shorten ballast life |
· |
Options for starting methods and lamp current
loadings |
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Requires compatibility with ballast |
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Low temperatures can affect starting unless
a "cold weather" ballast is specified
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HID Lamps |
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Require a ballast |
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Ambient temperature does not affect light output,
although low ambient temperatures can affect starting,
requiring a special ballast |
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Compact light source |
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High lumen packages |
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Point light source |
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Range of color temperatures and color rendering
abilities depending on the lamp type |
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Long service life |
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Highly efficacious in many cases |
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Line voltage variations, possible line voltage
drops, and circuits sized for high starting
current requirements must be considered
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Checklist for
specifying the right lamp for the application: |
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Light output |
· |
Input wattage |
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Efficacy (lumens per watt) |
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Rated service life |
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Size |
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Surface brightness |
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Color characteristics |
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Electrical operating characteristics |
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Requirement of additional equipment such as
ballasts |
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Compatibility with the electrical system |
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Suitability for the operating environment
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Light
Fixture Specification Checklist
A luminaire, often called a light fixture, is
a complete lighting unit that produces and distributes
light. It contains the light source, a ballast
if the lamp is fluorescent or HID, components
designed to diffuse or distribute the light
in a controlled pattern, components to protect
and position the lamp(s), and a connection to
the power source.
The light fixture's basic function is to
produce and distribute light to fulfill the
design goals for the lighted space. Below
is a checklist for specifying the right fixture
for the job.
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Characteristics
of The Space
First, the specifier must fully understand the
demands of the application and conditions in
the space that will affect the operation of
the lighting system: |
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Tasks to be performed in the space
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Desired light levels based on the tasks performed
in the space |
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Room size and dimensions |
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Structural obstructions such as beams |
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Layout of furniture and obstructions such as
partitions |
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Room and object surface colors and reflectances
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Special concerns such as safety and security |
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Hours of operation |
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Assessment of normal operating conditions |
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Possibility or known existence of abnormal
operating conditions |
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Cleanliness of the area during operation |
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Maintenance schedule |
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Availability of daylight
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Characteristics
of Lighting Components And The Fixture
Now the most appropriate light source can be
selected, followed by the fixture. The specifier
must understand the factors affecting fixture
selection: |
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Electrical, physical and operating
characteristics of the light source selected |
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Electrical, physical and operating characteristics
of appropriate ballasts |
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Electrical, physical and operating characteristics
of controls to be employed |
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Fixture efficiency (% lamp light output transmitted
out of the fixture) |
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Distribution pattern |
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Glare control |
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Finish |
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Appearance |
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Size |
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Accessibility of interior components for maintenance
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Ability to handle abnormal as well as normal
operating conditions |
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Aesthetics |
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