LIGHTING NOISE
Design Development Considerations For Fixture Selection, Dimmer Selection And Electrical
Systems Design
Performing Arts Center of Greater Miami
Miami, Florida
5 June, 1997
Artec Report No.
Artec Project No.
Distribution:
7263
3236
Architect:
Cesar Pelli and Associates
Attn.: Mitch Hirsch and Phil Bernstein
(1 copy bound, 1 copy unbound for distribution to the engineers)
Theater Planner: Fisher Dachs Associates
Attn.: Josephine Marquez
(1 copy, bound)
Clients:
Mr. Michael Spring, Executive Director
Metropolitan Dade County Cultural Affairs Council
(1 copy, bound)
PERFORMING ARTS CENTER OF GREATER MIAMI
LIGHTING NOISE GUIDELINES
CONTENTS
INTRODUCTION..................................................................................................................... 1
QUIET DIMMERS ................................................................................................................... 2
TYPES OF LIGHTING FIXTURES ...................................................................................... 6
Quiet Incandescent Sources .....................................................................................6
Fluorescent Fixtures and Remote Ballasts ...............................................................6
Neon and Cold Cathode Sources .............................................................................7
ROOM-SPECIFIC GUIDELINES .......................................................................................... 8
Auditoria—Performance lighting ............................................................................8
Auditoria—House Lighting .....................................................................................8
Rehearsal Rooms .....................................................................................................9
Control Rooms .........................................................................................................9
Other Spaces ............................................................................................................9
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Introduction
Many types of lighting fixtures make enough noise to be distracting in otherwise very quiet
performance and rehearsal spaces. We have addressed general noise control issues such as
fluorescent lighting, remote ballasts, and other similar electrical noise sources in our earlier
Guidelines for the Control of Noise and Vibration report. In the present report we focus
specifically on the acoustical aspects of non-incandescent fixtures and on noise of dimmed
incandescent fixtures used in performance lighting and house lighting in the auditorium, and
lighting in rehearsal spaces and other noise critical spaces. We recommend acoustical guidelines
for fixture selection and dimmer selection. We open these lines of dialogue at this point to allow
the theater consultant, architect and engineers to include the noise concerns in their detail design
and pricing.
The choice of incandescent fixtures must be coordinated so as to avoid producing objectionable
noise. In the most critical spaces (auditoria, stage, music rehearsal and coaching rooms), any
noise that is audible is objectionable. The goal in these spaces is subjective “quiet,” which is
different for each space and is quantified by the PNC noise criteria. For fixtures and dimmers
serving areas other than those mentioned specifically herein there are no special acoustical
criteria, except perhaps the physical location and mounting of the dimmers.
For permanent incandescent fixtures the dimmer noise criteria will be chosen as a function of the
noisiness of the fixture and the degree of quiet that is required in the particular application.
House lighting in the auditorium and dimmed lighting in rehearsal spaces and control rooms fall
into this category. Performance lighting instruments are not permanently connected to particular
circuits; so the dimmer selection must assume the noisiest fixtures.
With conventional dimmer technology at this point in time, making a dimmer quieter entails
using a larger filter choke and therefore entails somewhat greater cost. Recognizing that some
spaces with dimmable lighting must be very quiet and others need not be, we have found that it is
cost-effective to assign dimmer noise criteria in three grades. For the purposes of this report,
therefore, we shall refer to grades A, B, and C, with A the noisiest and C the quietest.
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LIGHTING NOISE GUIDELINES
Quiet Dimmers
Dimmer technology is evolving rapidly. While most of the change is in the control system and
user interface, there has also been movement toward quieter output. Noise is emitted directly
from the dimmer choke and semiconductors and from the cooling fans. While a single dimmer
may not make much noise, a room full of several hundred requires special attention for sound
isolation. But the main subject of this report is the noise generated by the lamp filament and
radiated by source and fixture.
Conventional dimmers (at present) vary the RMS voltage by chopping the 60Hz sinusoidal line
power with a fast electronic switch (SSR or SCR). Besides reducing the total power out, this
phase chopping transfers some of the electrical power into higher frequency harmonic noise that
is audible to humans. This chopped electrical power is more or less well radiated as acoustical
power by lighting sources, depending on the current through the source and the
electromechanical properties of the source and fixture.
Most dimmers (except the small, inexpensive ones sold for residential use) incorporate a filter
coil, called a “choke” after the power switcher for the purpose of reducing the radio frequency
noise (RFI) emitted by the dimmer, wire and lamp and for reducing audible noise emitted by the
lamp. A choke that will adequately filter out RFI can be relatively small and inexpensive, but it
takes a larger choke to quiet the lamp noise in the audible frequency range.
Over the last few years there has been increasing market pressure on manufacturers of theatrical
dimmers to develop better filters (and switches) for lower acoustical noise output at the fixture.
Theaters should not make any sound of their own, and it has taken several years for the
“electronic invasion” into theater to recognize and begin to deal with its own problems; still,
there has been progress, and we expect the advances to accelerate. Present off-the-shelf
technology includes “high rise time” dimmers from most major manufacturers, a traditional
approach wherein the filter choke is large enough to smooth out the chopped waveform
significantly. The cost is slightly lower electrical efficiency, greater expense and greater space
requirements. Hopefully, as the manufacturers learn how important quiet dimmers are, they will
intensify the competition and develop new technology.
At this stage of this project we do not yet know what will be the most appropriate technology for
low-noise dimmers, so we cannot yet put forward firm, but attainable, specification criteria for
low noise. We agree with FDA that during the development period between now and tender for
the dimmer package the design team should keep the options open by keeping collective watch
on the dimmer R&D at the major manufacturers and accommodating the broadest possible range
of technologies into the building infrastructure.
Artec has developed a specification for testing the acoustical noise output of a variety of
dimmers. We will continue to refine this with FDA in measuring candidate dimmers for the
performance spaces. In addition to rise time and rate of rise measurements at the dimmer, we
measure the frequency spectrum of the electrical power and of the acoustical power radiated by
the source and fixture. But the most important tests are careful subjective listening tests. We
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correlate the listening tests with the measurements and with samples of other “known” dimmers.
We recommend that the team consider specifying three “acoustical grades” of dimmers in order
to allow the project to afford the quietest possible dimmers in the most noise-critical spaces and
take advantage of lower prices for the spaces that are not as critical, such as lobbies.
Electrical noise output from the dimmer and the ensuing acoustical noise radiated from the light
are a function of the load on the dimmer. Dimmers are generally quietest at full load, and noisier
at anything less than full load. For this reason it is essential that all dimmers serving fixed
circuits in noise critical spaces be loaded to the maximum allowed by code (usually 80% of the
dimmer’s nominal maximum load). This must be kept quite consciously in mind as the circuiting
is designed; mixing of 2.4k and 6k dimmers is sometimes appropriate to achieve the full load
goal.
Although the dimmer rise time alone will not be the deciding factor as to what is “quiet enough”,
we can outline the current state of the art for dimmers we have specified, tested and used on other
North American (120v) projects to provide a starting point for the development and pricing:
Dimmer Type
Max Load (kW)
Test Load (kW)
Min. 10%-90% Rise
Time (µs) @ 90°
firing
A (Standard)
2.4
2.0
350
6.0
6.0
350
2.4
2.0
500
2.4
1.0
500
6.0
4.8
500
2.4
1.0
800
6.0
4.8
800
B (Superior)
C (Critical)
We note that most manufacturers offer 500µs rise time dimmers for only slightly higher cost than
their 350µs models and substantially lower cost than their 800µs modules. Artec, FDA and CPA
will need to coordinate to select the dimming modules and fixtures that are silent and technically
and aesthetically suitable. We note that in no recent project has it been necessary to use dimmers
with rise times greater than 800µs. Dimmers with rise times above 800µs will only be necessary
if custom or particularly noisy fixtures are required. Such dimmers are not readily available from
the present probable suppliers of dimming equipment.
There is much new technology in the lighting marketplace, and Artec is willing to consider and
test (perhaps participate in the development of) new technologies in quiet lighting systems. For
example, so-called “intelligent” dimmers that chop the incoming waveform in a more random
fashion, and variable-focus fixtures that are supplied with specialized, matching dimming
equipment are technologies that may be appropriate for the Performing Arts Center of Greater
Miami. Most “intelligent” dimming systems have equivalent rise times of 800µs and are
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LIGHTING NOISE GUIDELINES
comparable in noise level to other Type C dimmers of a more conventional design. Variable
focus fixtures have only recently become available without integral cooling fans and are now
worth consideration. We are concerned that the typical lamps used in these fixtures may still be
prohibitively noisy, and encourage immediate investigation of their potential use.
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We will work with FDA to refine the criteria for Type A, B and C dimmers on this project. The
guidelines below assume that the dimmers to be prequalified for the Performing Arts Center of
Greater Miami will be at least as quiet in each of the three categories as the current products that
fall into these categories.
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Types of Lighting Fixtures
The combination of lighting fixture and dimmer ultimately determines the amount of noise
generated by the lighting system. However, certain fixtures are more prone to radiating filament
noise and certain lamp types (filament types) are noisier than others. The following is a brief
discussion of the noise associated with different types of light fixtures.
Quiet Incandescent Sources
If electronic dimmers did not chop the incoming electrical signal to reduce power, almost all
incandescent fixtures would be quiet. But given the technology we have to work with, it is
prudent to make some assumptions and give some guidelines on the fixture types where possible
so that the dimmer/source combination is quiet. In the next section we provide some guidelines
for specific rooms. It is likely that the Architect and Engineers are proceeding with designs that
are mostly in compliance with these recommendations, and all but a few fixtures that are not
acoustically acceptable can usually be made acceptable through usage of a different source
(lamp) than the standard element supplied by the manufacturer.
Fluorescent Fixtures and Remote Ballasts
In fluorescent lights the ballast generates “hum” and the discharge of the gas in the tube
generates additional high-frequency energy. Ballast hum is generally the worse of the two
problems. Some of the new “electronic” ballasts are quieter than the average ballasts, but even
so, most of them contain a small transformer or some device that generates audible hum.
The Advance Mark VII ballast is still the only ballast available in North America that is silent
enough for noise-critical spaces rated PNC-20 and below. No North American fluorescent
fixture is silent enough for application in the critical performance spaces except as work lighting.
Fluorescent lighting is not acoustically acceptable for house lighting, exit lights or aisle lights in
the auditorium. (It is not usually acceptable in for house lighting from a color temperature point
of view either.)
Fluorescent lighting is acoustically acceptable in certain of the other noise-critical spaces, but in
those cases the ballasts must be mounted remote from the room. The requirements for spaces
with remote ballasts will be determined during this phase of design and locations for remote
ballasts will be identified on the electrical drawings.
In general, remote ballasts should be located outside of, but nearby to the space they serve. The
cabinet containing the ballasts will, in most cases, have to be mounted on the floor or hung on the
wall with neoprene isolators as described in the electrical specification.
Where remote ballasts are used, the electrical engineer should confirm that the ballasts specified
are capable of driving the load wiring and that the conduit provided will accommodate all the
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wire required.
Neon and Cold Cathode Sources
Neon and cold cathode lighting are not acceptable in noise critical spaces. To date, we have not
heard of any desire to use such lighting on this project.
LED Lights and low-voltage incandescent
What to say?
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Room-Specific Guidelines
Auditoria—Performance lighting
There are many types of theatrical fixtures—many of them high-wattage—and there are no
permanent connections between fixtures and circuits. The facility users will move fixtures from
place to place depending on the particular production. Furthermore, the technology of theatrical
fixtures will continue to evolve, and fixtures will be replaced or augmented before the dimmer
system is replaced. Since just one or a few noisy fixtures can ruin the theatrical experience for
many people in the house, this problem must be addressed as far as possible at the dimmer.
Performance lighting fixtures range from moderately quiet (500w mini-ellipsoids) to moderately
noisy (1k FEL) to very noisy (PAR-64). Owing to the high wattage and the proximity of fixtures
to the ears of the audience, dimmers for front-of-house circuits should be Type C. Type C is
acoustically preferred for on-stage and circuits in the acoustic canopy of the Concert Hall, but,
depending on budgetary constraints, it may be necessary to step back to Type B for performance
lighting circuits (non-concert lighting) in the Concert Hall and Ballet/Opera House stage. With
present technology Type B and C dimmers have different voltage output for the same input,
owing to the different losses in their filters. The solution may be to provide some sort of voltage
regulator on the line serving either the Type C dimmer racks or the Type B dimmer racks. With
the advent of self-regulating dimmers there may be another option: supply a single voltage to all
performance dimmers that is high enough to drive the Type C dimmers to full output, and let the
Type B dimmers regulate their own voltage back to nominal 120v. The theater consultant should
consider the related performance and technology issues and discuss the alternatives with the
electrical engineer.
Motorized color changers, variable focus and other recent advances create noises that we have
not had to contend with on past projects. Our collaborative selection of these devices and draft
specification should be issued in enough time to allow selection or development of quiet versions
of any such technologies.
Auditoria—House Lighting
We recognize that maximum flexibility must be given to those designing the house lighting. We
also understand that the auditorium lighting concept includes only incandescent fixtures. For
high-wattage luminaires use quartz sources.
Many of the house lighting fixtures will be very close to the ears of the audience; so the
dimmer/fixture combination must be truly silent at close range. It is imperative to use Type B or
Type C dimmers for house lighting. Load all house lighting dimmers to the maximum allowed.
Certain types of fixtures will require Type C dimmers—Artec will coordinate with FDA and
CPA in selecting the appropriate dimming equipment.
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If low-voltage sources are to be included, the transformer(s) must be located outside of the noisecritical space. Note that aisle lights in seats and steps and/or exit signs may fall into this
category.
Rehearsal Rooms
Quartz downlights are usually desirable in music rehearsal rooms to attain high intensity for
reading music. Acoustical preference is for more 500W fixtures rather than fewer 1kW fixtures.
Quartz sources are acoustically recommended, and can be made quiet enough by choice of quiet
dimmers as discussed below. If fluorescents are used in rehearsal rooms, the ballasts must be
remote (outside the room).
The high-wattage downlights and absence of background noise required for music rehearsals
leads us to choose Type B dimmers for the Orchestra and Chorus rooms. Load all rehearsal room
dimmers to the maximum allowed.
Control Rooms
Dimmed task lights are often used in control rooms. Although they are not usually high-power
sources, typical R- or A-type sources are noisy if not supplied by quiet dimmers. If the central
performance dimming system is used to control these spaces, Type B dimmers would be
acceptable for these rooms. If local dimmers are used, then use autotransformer dimmers, but
consider the hum radiated by the autotransformer itself. We will consider other quiet
alternatives. The sound and broadcast and staff viewing rooms are more critical in this regard
than the stage manager and lighting control rooms.
Any fluorescent fixtures in control rooms should have remote ballasts (which should not be
located in the auditorium sound locks).
Other Spaces
All other spaces with dimmed incandescents may use standard Type A dimmers (no acoustical
criteria).
We believe that Cosentini’s engineers plan to locate the dimmers serving the public spaces in a
dimmer room close to the center of the load, and will serve them from the general power system,
not the performance lighting transformer.
We assume that the principal dressing rooms would not include dimmed incandescent fixtures,
and are therefore not addressing those spaces here.
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END OF REPORT
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