BR>challenge is in trying to maintain, if not enhance, the
quality of the lighting in these existing spaces while
complying with stringent energy codes.
It is difficult to establish a strategy for meeting this
challenge without extensively examining the existing
lighting system beforehand. In fact, it is a big mistake
to assume that simply adding more efficient lamps and
ballasts to a room full of existing fixtures is the best
way to save energy.
To help establish a strategy for planning retrofits, it helps
to develop a simple lighting audit procedure. Audits help
establish the condition of an existing lighting system and
the architectural finishes of the space and assess the
interaction between the lighting and the occupants. Most
importantly, an audit provides benchmarks for determining
how effective the lighting improvements will be during
and after the completion of the design process.
Site Visit
A site visit to examine the specific characteristics of the
existing lighting system is the keystone of the audit.
Below are suggested steps to follow:
1. Note the age, condition, and quantity of the existing
light fixtures. If there is no accurate reflected
ceiling plan with dimensions, this is the time to
make one.
2. Record the manufacturers and model numbers of the
fixtures to help establish photometrics.
3. Record the wattage of the lamps, the ballast types,
and model numbers.
4. Note the condition of the fixtures. Are the lenses
yellowed or cracked? If so, they are probably at the
end of their useful lives. Observe the painted sur-
faces. Are there burn marks or greasy smudges? Is
there yellowing? Deterioration of the fixtures causes
excessive loss of efficiency.
5. Ascertain the environmental conditions of the space
for dirt depreciation. More dirt will accumulate in
fixtures placed in a sandblasting shop, say, than in
an office. This will aid in specifying an appropriate
replacement fixture that will minimize future main
tenance costs.
6. Note the activities of the end-users in the space.
Pay particular attention to occupants ages, and
what type of work is being performed.
7. Observe and record how the lighting is switched,
and establish whether there are any automated light
ing controls or another type of lighting control system.
8. Check all work surfaces with a light meter to estab-
lish existing lighting levels. Note the coloration and
reflectances of the walls, floors, and ceiling in the
space, and establish all other calculation criteria for
the space. This will facilitate the use of lumen
method and point-by-point calculations for the
replacement lighting system.
Reverse Engineering
Once all of this basic information has been recorded and
digested, one can begin to make some useful conclusions
about the current lighting system.
Look at the original intent of the space and the
related costs of operating the lighting system
installed there. Does the existing system still provide
an appropriate level of light for the space as it is
now used? Are energy and maintenance costs in
line with this use?
Run some rough lumen method or point-by-point
calculations to establish the illumination levels the
original lighting system was designed to produce.
Compare them to the light meter readings. This will
give a good idea of how much the current system
has deteriorated.
Establish the existing lighting power density. How
efficient is the existing lighting system in terms of
watts per square foot? How efficient is it in terms
of the amount of light actually available at the
work surface?
This information gives us a basis for deciding how to
improve the lighting systems efficiency and also helps
justify improvements regarding aesthetics, ergonomics,
and the cost of maintaining and operating the new light-
ing system.
A Hypothetical Problem
Imagine an insurance form processing center located in
a high-rise office building. Originally an open office, it
has now been subdivided by seven-foot high partitions
into 8x10 cubicles. The walls bear 10-year-old paint,
the ceilings are stained, and the vinyl floor tile has not
been maintained.
The lighting system in this space is a virtual sea of fixtures,
all in terrible condition. The lenses are yellowed and caked
with dust. The ballasts are old, core-and-coil types.
The light meter reads an average of 65 footcandles at the
work surface. By looking up the photometric data of the
Kilojolts Consulting Group, 594 Marrett Road, Suite 10, Lexington, MA 02421 | 781 861 6800 | garym@kilojolts.com
How to Conduct a Lighting Audit
Published in Plant Engineering Council 1993 Journal
Gary Markowitz, IES fixture, and making some assumptions about the reflect-
ances of the walls, floor, and ceiling, it can be calculated
that the system was originally designed to produce 110
footcandles at the work surface. The unit power density
is 3.5 watts per square foot.
Although the occupants feel the lighting level is adequate,
the facility owners are paying more for lightalmost
double the amountthan theyre actually getting.
Apparently, there is room for some improvements here.
Now that it is known how inefficient the existing lighting
system is, we can establish energy savings and ergonomics
goals by looking at two numbers: unit power densities
and recommended illumination levels.
On any project, the first step is to examine local energy
codes to establish a maximum allowable unit power den-
sity. Generally, it is a good idea to try to use an even
lower unit power density than thisthe incremental cost
can easily be justified by the extra energy savings, and
utility company rebates can often help further offset any
additional cost.
Next, consult the reference lighting handbook of your
choice to determine what lighting levels are suitable for
your project. Remember that the quality of the luminous
environment is more important than providing a high
quantity of lightin many cases buildings are overlit, and
less light will result in better vision.
When comparing energy saving strategies, always com-
pare the costs for both a system retrofit and a complete
system replacement.
Two Hypothetical Solutions
Solution 1
Complete Re-Design
In this scenario, the lighting system is redesigned from
scratch. The lighting level is decreased from 110 foot-
candles to 65 footcandles by using fewer, more efficient
fixtures with high efficiency components. This also
reduces the connected unit power density to about 1.2
watts per square foot. Additional energy savings are
realized through the addition of a relatively sophisticated
control system.
The lighting fixtures might include parabolic troffers with
energy saving color-corrected fluorescent lamps (3,000K
to 3,500K) and electronic ballasts. The control system
might have pre-programmed occupancy scheduling, with
telephone actuated after-hours override. The wiring to
the fixtures could be split to allow one or two lamps to
be dropped out after hours to correspond with building
maintenance or security activities.
To make the most of the improved lighting system, the
entire room would be refinished with new materials with
better reflectance values.
Solution 2
Retrofit
In this scenario, the lighting system is remodeled,
eliminating the cost of wiring new circuits and hanging
new fixtures. The lighting level is lowered from 110 to 65
footcandles by eliminating lamps and adding reflectors,
new aluminum parabolic louvered door assemblies, elec-
tronic ballasts, and energy-efficient lamps. The connected
unit power density remains slightly higher, at 1.5 watts
per square foot, because fewer fixtures could be eliminated
than in the first solution. Time clock activated occupancy
sensors help save additional energy, although they are not
as effective as the control strategy in the first scenario.
Take No Chances
Changing a facilitys lighting system to meet todays
energy guidelines without losing quality doesnt happen
by chance. Even a thorough, well-intended retrofit using
all the right tools to reduce energy can still be wasteful if
lighting levels remain too high. Conversely, a retrofit that
neglects the needs of the users can drastically cut visual
comfort and productivityand that gives energy conser-
vation a bad name. A well-planned and thorough audit
procedure helps establish a basis for improving energy
efficiency without leaving users in the dark. Kilojolts Consulting Group, 594 Marrett Road, Suite 10, Lexington, MA 02421 | 781 861 6800 | garym@kilojolts.com
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