Can the color of lighting affect the energy
efficiency of lighting systems? According
to the Department of Energy, the
answer is yes.
When the spectral properties of ambient
lighting are shifted to be more like the color
of daylight (more white), our eyes respond
the same as if lighting levels were increased
— the pupils of our eyes get smaller, spaces
seem brighter, and we see things more
clearly.
The DOE’s solid-state lighting portfolio
activities target improvements in the efficiency,
performance, lifetime, and quality
of light from both organic and inorganic
light emitting diodes. Solid-state lighting
systems have the potential to more than double
the efficiency of today’s systems, and
these research and development efforts represent
an essential component of meeting the DOE's Building Technologies Program’s
energy efficiency goals.
Still, a mix of lighting solutions will be
needed to meet our nation’s near-term and
long-term needs. Spectrally enhanced
lighting is a simple strategy that uses existing
products and technology to significantly
reduce energy use in commercial
buildings.
The Cost of Lighting
According to the Buildings Energy Data
Book, energy consumption for all lighting
in the United States is estimated to be
about 18 percent of the total electricity
generated in the country. More than half
of the energy is consumed in the commercial
sector, where lighting coincides with
peak electrical demand and contributes to a
building’s internal heat generation, increasing air-conditioning load.
The conversion of electricity into useful
light is one of the least efficient energy
conversion processes in buildings
today. The DOE says advanced lighting
technologies can significantly improve
the energy efficiency of lighting and reduce
building energy consumption and
costs.
The concept behind SEL: A significant
amount of energy can be saved by using
lamps that have less light output, but higher
correlated color temperature (CCT). Lamps
with higher CCT appear brighter than those
with lower CCT, so the actual light output of
higher CCT lamps can be decreased, while
maintaining equivalent perceived brightness
and visual acuity.
Thus, energy can be saved because the
actual light output of the higher CCT lamps can be decreased, while maintaining
equivalent perceived brightness and visual
acuity relative to lower CCT lamps.
Energy savings are achieved by using
lower wattage lamps and/or lower ballast
factor ballasts.
Unlike other energy efficiency strategies,
SEL is not a technology — it’s a different
way to quantify light that can be used with
any type of lighting design to improve energy
performance. Energy savings are
achieved by using high performance and
high CCT lamps coupled with efficient
electronic ballasts.
The DOE says SEL is a market-ready,
cost effective solution for quick energy savings.
It is simple to implement, and can currently
be employed in buildings as a cost
effective way to get quick energy savings. It
is non-proprietary, requires no fancy controls
or gadgets, and the energy savings are
significant. In addition, SEL is low risk, and
DOE says there are no known negatives to
installing this type of lighting in commercial
buildings.
An evaluation of lighting retrofits at three
office buildings in California in 2005 conducted
by Pacific Northwest National Laboratory
(PNNL) for the DOE Building
Technologies Program found energy savings
are achieved via lower wattage lamps
and/or lower ballast factor ballasts.
In the Spectrally-Enhanced Lighting Program:
Implementation for Energy Savings
demonstrations, existing fluorescent lamps,
from 3000 to 4100 Kelvin, were replaced
with lamps of 5000 Kelvin. Normal ballast factor
ballasts (0.88) were replaced with
new electronic ballasts with ballast factors
ranging from 0.60 to 0.77.
The demonstrations were designed to decrease
lighting power loads in the three
buildings by 22 percent to 50 percent, depending
on the existing installed lamps and
ballasts. The buildings were a 57,000-
square-foot office building located in Santa
Rosa, Calif., in which 1,700 T12 lamps were
replaced; an 119,000-square-foot office
building located in Vallejo, in which 2,800
T8 lamps were replaced; and a 67,000-
square-foot office building located in Oxnard,
in which 2,300 T8 lamps were
replaced.
The project designers hypothesized that
this reduction in electrical loads could be
achieved by the change to higher CCT
lamps without decreasing occupant satisfaction
with the lighting. During a six-month
period, PNNL performed field measurements and occupant surveys before and after
the lighting retrofits were completed.
PNNL measured the following: overhead
lighting electrical loads, light levels in
the workspace, task lighting use, and occupant
ratings of satisfaction with the
lighting. The analysis compared pre-retrofit
to post-retrofit conditions in these
four areas.
Electrical loads (kW) and consumption (kWh) by the overhead lighting equipment
were measured by installing data logger
meters on the lighting circuits at the lighting
control panel. Data were collected for
at least two weeks under the pre-retrofit or
baseline condition (in which existing
lamps were replaced with identical new
lamps and the fixtures were cleaned) and
for at least two weeks following the retrofit
with the new higher CCT lamps and new ballasts.
The logging meters were configured to
record average overhead lighting loads (in
kW) in five-minute intervals 24 hours per
day during the monitoring periods. In addition,
connected load measurements were
taken on a sample of fixtures in each building
during the baseline period and in the
post-retrofit period.
Pre-retrofit and post-retrofit illuminance
measurements were taken at representative
spaces in each building before and after
retrofit. The instrument used for all measurements
was a combined photopic/scotopic
meter. The human eye has two types
of photoreceptor cells, known by their
shape as “cones” and “rods.” The photopic
luminous efficiency function describes the
sensitivity of the cone-shaped photoreceptor
cells to all the wavelengths in the visible
spectrum. The rod-shaped photoreceptor
cells have a different sensitivity curve,
called the scotopic luminous efficiency
function.
Standard light meters are calibrated to the photopic response. Use of a photopic/scotopic
meter allowed for measurement of the scotopic illuminance levels and calculation
of the scotopic to photopic (S/P) ratio. The
S/P ratio provides an easily referenced indicator
of relative blue content in the light
source. Most light sources have S/P ratios
ranging from 0.8 to 2.5, with the higher values
containing more energy in the blue
wavelengths of the visible spectrum.
Pre- and post-retrofit task lighting use was
monitored to assess whether people compensated
for the lower overhead light levels
by using their task lights more frequently.
In all three buildings, under-cabinet
mounted task lighting fixtures of 15-40 watts
were present. The frequency of task lighting
use was monitored with portable data
loggers installed in a sample of task lights
in each building. Data were collected for
about two weeks in both the pre- and postretrofit
periods.
PNNL’s evaluation found that connected
loads due to overhead lighting in the three
buildings decreased by 20 percent to 46 percent
following the retrofit. Horizontal photopic light levels decreased by 15 percent
to 31 percent. Task lighting use did not change
significantly, as indicated by metered use or in
terms of occupants’ reported use. Finally, occupant
ratings of satisfaction with the lighting did not
change significantly following the retrofits in any
of the three buildings. Appropriate lamps are
available through many major lamp manufacturers and
are generally no more expensive than traditional
lamps. The predominant light source used in
commercial applications is fluorescent lighting; the
lamps and ballasts used dictate the efficiency of
fluorescent lighting systems.
Using higher color
temperature, fluorescent lighting and new
high-efficiency ballasts can achieve energy savings
of 20-40 percent compared to traditional fluorescent
lighting systems, according to results of the DOE
study, and can be achieved by simple lamp/ballast
retrofits.
FSM Source:
“Spectrally Enhanced Lighting Program Implementation
for Energy Savings: Field Evaluation,” prepared by
Pacific Northwest National Laboratory for U.S.
Department of Energy Office of Energy Efficiency and
Renewable Energy Building Technologies Program.
