From Pokemon to Tiffany's to LEED to DALI - Illuminating ...

in the US. Europe is accustomed to
saving energy in lighting by providing
soft, indirect illumination. This provides
user comfort with the least
amount of expended energy.
Luminaires also have dimming systems
that reduce light levels when
rooms are unoccupied and when daylight
is available.
But with the cost of electricity on
the rise in North America, the Department
of Energy has endorsed a new
energy conservation requirement for
office lighting in the US. The
ASHRAE/IESNA 90.1-1999 lighting
standard and the new International
Energy Conservation Construction
code (IECC) are fast becoming law in
all 50 states. Maximum lighting
power densities (LPDs) are allowed
for interior lighting, and controls
must be employed to limit the use of
electricity when offices are unoccupied.
Daylight, when available, is recommended
to supplement or replace electric light.
Which is why more and more new luminaires for use in the
U.S. are going green. An example is a fixture design with a combination
occupancy and daylight harvesting sensor integrated
into the luminaire. This is particularly suited for perimeter
offices with exterior windows.
Occupancy sensors used in Europe have already been
shown to reduce lighting energy loads by 25 percent to 40
percent, depending on how long the occupant is away from
the office. On average, an office is occupied two-thirds of the
business day, or 1875 hours out of the normal 2800 working
hours of the year.
Tests have shown that properly designed daylight “harvesting”
saves as much as 50 percent of the lighting load, depending
on the latitude and climatic conditions of the site and the
orientation of the building. In an office occupied only 1875
hours a year, the power saved by utilizing daylight reduces the
lighting load, conservatively, by 40 percent.
For example, in a typical 160 square foot exterior office, with
an allowable LPD of 1.5 watts per square foot (240 watts), an
eight-foot pendant-mounted luminaire with four 54W T5 HO
lamps just meets that connected load maximum. An occupancy
sensor would save one-third of the lighting load, and a daylight
harvester, connected to dimming ballasts, saves an additional
40 percent of the lighting energy during occupancy. The
two sensors working together yield a total load reduction of 60
(above) An integral automatic daylight/occupancy
sensor can be less obtrusive and costly
than installing separate sensors.
(opposite, top) In low-daylight conditions,
"sensor" luminaires automatically provide full
light output, for comfortable indirect lighting.
(opposite, middle) Throughout the day, the
fixture gradually adjusts light output to balance
artificial illumination and daylight.
(opposite, bottom) The luminaire automatically shuts
itself off when no one is present, significantly
reducing energy use.
percent, or 144 watts. That lighting
load reduction will save an additional
36 watts in air conditioning load, for
total energy savings of 180 watts.
In an area of the U.S. where the
electric rate over the next ten years is
expected to average $.13 a kilowatt
hour, the cost savings are 180 watts x
2800 hours x $.13 per kilowatt hour,
or a total of $65.50 per year.
Based on this example, the “green”
fixtures would provide a return on
investment of 22 percent and the initial
investment for sensors and digital
dimming ballasts would be paid off in
4.6 years. Separate sensors installed in
the room by an electrical contractor
would be much more expensive, and
not nearly as inconspicuous. The
green fixtures react subtly to changes
in available daylight to avoid being
distracting to the occupant of the
space. In addition, the user has the
ability to adjust the light level manually
via a remote control unit. And, since the digital dimming ballasts
are DALI-compatible, the building owner has the option to
integrate the fixtures into a larger DALI control system later on.
The New York State Energy Research and Development
Authority (NYSERDA) has a lighting energy conservation program
that rebates $70 for every luminaire with self-contained
sensors used in that state until June 2003. This could increase
the return on investment to 28.5 percent and reduce the payback
for a sensor-operated fixture to 3.5 years. Should energy
costs rise by only 10 percent, the return on investment increases
to 31 percent and the payback would be further reduced to
3.2 years.
But, are economics the only reason for an organization to
invest in green technology What about corporate values –
could it be that in this time of ethical turmoil, corporate sustainability
will come easiest to those who are committed to a
higher purpose If so, what purpose could be higher than saving
the planet
The author: Wolfgang Egger is president of Zumtobel
Staff Lighting, Inc., Highland, NY. Mr. Egger is a graduate
of the Technical University, Vienna, Austria, where he
received a Ph.D. in Physics. He has been a member of the
IESNA since 1986.
www.iesna.org
LD+A/January 2003 23