EDUCATION
T
he other day, while discussing
LED street lighting, a city official
told me that he wants to wait until
LEDs “are here.” His opinion was
that LEDs are not yet ready for prime time.
As we talked further, it became clear that
he knew very little about LED technology, IES testing standards, DOE Gateway
projects, or much else about LEDs. This
conversation reminded me of a campus
facilities manager who’d told me “I tried
LEDs. Didn’t like ’em.” That’s like saying,
“I’ve tried soup. Didn’t like it.” What kind
of LED did he try? What color temperature
was he looking at? What type of optics
and lensing were used?
This far into the LED revolution, it’s a
The 7 Habits of
Highly Selective
People
BY PAUL MITCHELL
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Even though the revolution
is well underway, too many
owners and end users are
still blissfully unaware of
what they need to know
about LEDs. Here are seven
good places to start
concern that many end users and other
decision-makers are not yet up to speed
on the fundamentals of today’s technology.
Ironically, while the Municipal Solid-State
Street Lighting Consortium continues
to promote LED education and produce
helpful tools, this lack of understanding
seems uncomfortably common among
the aforementioned city officials, college
campus officials, utilities and developers.
Many people still find themselves lost in
the forest of information (or misinformation) regarding what is and isn’t true about
today’s LEDs. Just as there are key items
that everyone would want to have if they
were lost in the woods (a compass, a
lighter, Cherry Coke, Funyons, etc.), there
are key considerations for safely navigating today’s landscape of LED options.
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EDUCATION
1. Why Consider LED?
2. Say Watt?
odes and micro optics, more circuit boards,
The primary benefits of LED over tradi-
Further mitigating the importance of en-
tional light sources are fourfold: immediate
ergy savings, watts aren’t the primary mea-
energy savings, long-term maintenance sav-
suring stick anymore—lumens are. People
You don’t want to be paying for lumens
and possibly more heat sink required in the
higher wattage version.
ings, improved directionality and adaptability,
generally know what lumen output they
that are going up and out, but rather the use-
and an improved quality of light, particularly
can expect from a 150-W HPS lamp, but 150
ful lumens that are being directed down into/
when converting from HPS. Some funding
watts can produce entirely different lumen
onto your target area. Note, however, that
opportunities are tied to energy savings, but
output in different LED luminaires. Watts
some LED fixtures are offered with only one
the truth is that maintenance savings is gen-
are certainly important in terms of calcu-
LED array, opting to provide higher or lower
erally what really provides the payback, par-
lating energy savings, but they’re not the
lumen output simply by varying the drive
ticularly when/where energy is cheap. Some
key metric to use when comparing LED to
current. In these cases, the fixture will most
customers produce their own power, or have
HID, or even LED to LED. Wattage will vary
likely cost the same regardless of its po-
access to relatively cheap hydro power, so
based on several factors, such as the drive
tential lumen output or variance in required
their potential energy savings are minimal.
current of the LED array and the number of
wattage. Directing lumens downward is not
Many people have already found that the
diodes used. What one fixture produces us-
to be confused with recommending narrow
ROI on LED, when based solely on energy
ing 90 watts may be vastly different from
beam patterns that produce hot spots and
savings, just isn’t cost effective; it’s too long-
what another fixture produces using similar
significant reflective light off the ground.
term. Still, LED makes sense to many cities
wattage. Generally, you’re going to signifi-
You can still have a responsibly wide beam
and universities because they're going to
cantly cut your wattage when going from
pattern, producing improved uniformity and
reap not just the energy savings, but the long-
traditional light sources to LED. But saving
reducing material and installation costs.
term maintenance benefits. Conversely, for a
10-15 watts may not be the way to go if the
But light that is uncontrolled, going out
developer who’s going to build and then sell
light output is significantly lower than an-
sideways and up is not what you want to
the project, the upfront premium to use LED
other luminaire with slightly higher wattage,
be paying for. Remember that the increased
may not make sense.
especially if the lower wattage luminaire
directionality and control offered by today’s
Directional control is much higher with
requires you to use more fixtures in your
LED fixtures over older HID lamp and optic
LEDs, generally given to the move from
overall site plan, increasing your long term
combinations is part of what allows them to
single lamp/single optic design, to utilizing
energy and maintenance costs, as well as
produce equal or better light using less total
multiple light sources (often dozens), each
your upfront material and installation costs.
lumens, and significantly less energy. This
3. Please Keep it Down.
night sky should be considered.
with its own finely tuned micro-optic. This
approach allows for very sharp cutoff near
is where BUG ratings and protection of the
property lines, as well as new hybrids of
While lumen output is important, the
the standard IES distribution patterns. This
most emphasis should be placed on a lumi-
4. Get a Life.
leads to better lighting design, offering the
naire’s downward delivered lumens, not its
The proper way to evaluate the LED ROI
designer more powerful tools to put the light
total lumen output. With HID fixtures, the
is through life cycle analysis, not unit price
exactly where they want and only where
difference in manufacturing cost between
on bid day. Look at the life cycle of the LED
they want. The benefits in lighting quality,
a 70-W version and a 250-W version of the
system, say 100,000 hours for the sake of
moving from a HPS environment to a broad
same fixture is negligible (unless you’re go-
discussion. Then look at the comparative life
spectrum white light environment, such as
ing to a larger housing, just for aesthetic
cycles of other light sources being proposed,
warm LED, are well documented, and in-
purposes). For many LED fixtures, the dif-
such as HID or induction. It is critical to note
clude dramatic improvement in CRI, visual
ference between a 70-W luminaire and the
that these life cycles are based on differ-
same fixture using 250 watts can be signifi-
ent metrics. The “useful life” of an LED has
cant. You’re probably talking about more di-
been defined as its hours of operation to L70
acuity, contrast, and more.
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EDUCATION
(a 30 percent depreciation in lumen output),
maintains the proper case temperature.
long period of time, without any maintenance,
whereas the life of HID lamps and induction
That’s really the life span that you want to use
they must have their own defense against
systems are based on their failure rates.
in your ROI calculations, because regardless
both water and particulates, such as dust and
Metal halide lamps are generally rated to a 50
of the condition or depreciation of the diodes,
dirt. Otherwise, your diodes could be shining
percent failure rate, whereas HPS lamps are
that’s when you’ll actually need to make a
(and corroding) under water, or trying to emit
generally rated to a 33 percent failure rate.
maintenance visit to the fixture.
light through a filthy lens. An IP rating of 65
Induction generally has a 100,000-hour life
Consider also that when the driver fails,
is a good base for most outdoor street and
rating, but that’s to a 50 percent failure rate.
it might be prudent to consider changing/
area applications. The ‘6’ indicates complete
So using that example, compare the energy,
upgrading your LED array. If the projected
protection against the entry of dust, and the
material and maintenance cost of an induc-
life of the driver is 23 or so years, think what
‘5’ indicates protection against low pressure
tion system where 50 percent of your units
we’ll be doing with LEDs by then. With the
jets of water from all practicable directions.
will have to be replaced in the same time that
speed at which efficacy is improving, you’ll
A well-engineered luminaire, regardless of
it will take the LEDs to depreciate to L70 with
be able to dramatically reduce your energy
the light source, should probably have an IP
little/no projected failures.
consumption and still maintain the light
rating of 65 or higher for at least the optical
levels you originally designed to.
chamber, if not the entire luminaire.
For outdoor applications, the cost of
changing a lamp is generally several hun-
Remember there are other components
7. Get Used to Change.
dreds of dollars, per fixture, per event. Over
in the fixture, such as gaskets, lensing, pho-
a single “useful life” span of an LED luminaire,
tocells or controls components, which will
In the world of LEDs, lumen output, avail-
you may need six to eight visits to that fixture
eventually need to be repaired or replaced.
able CCTs, optional drive currents, etc.
to relamp an HID luminaire, each time incur-
Related to this, a shift that’s taking place in
change quickly as new diodes become avail-
ring not only the cost to send a couple of guys
LED site design is the cessation of relying
able. The same is true of some of the newer
with a bucket truck, but the cost to replace
on an individual button-style photocell to
HID lamp technologies. You can’t rely on
the failed component(s), divert traffic, do the
operate each fixture, a common practice
printed brochures; the technology and prod-
initial trouble-shooting, etc. These additional
in HID site design. If you’re going to invest
uct offering changes too quickly now. Most
costs need to be considered on top of the en-
in LED, then it’s worthwhile to explore the
updates are provided via PDF or posted
ergy savings that the LED unit will provide over
expanding offering of wireless controls. If a
online at the manufacturer’s website. How-
that same life span, and most likely none of us
PEC is absolutely necessary, a utility grade
ever, you also shouldn’t rely on info from the
expect energy costs to go anywhere but up.
twist-lock PEC is much more reliable than
website if you’ve not checked it in a while.
the button style. If you must use a button
Before making any final decisions, return
5. Get a Real Life.
style, then consider controlling a number of
to the manufacturer’s website to check for
While a fixture’s L70 rating is an important
fixtures from one PEC, rather than having
updated information. There may be newer
metric, you must also consider the life of the
one in each fixture. Either way, recognize
options available to make your project even
driver. Because LEDs last so long and depre-
that the button approach puts the burden of
more energy-efficient, or to reduce your up
ciate so slowly, one of the reasons for L70 was
your entire lighting system—and all of your
front and/or long term costs. ■
to answer the question, “If LEDs don’t fail for
projected maintenance savings—on the
such a long time, how do we know when it’s
shoulders of a $5 component.
time to change the lights?” While the actual
LED array may not “fail” on its own, the array
6. Got Protection?
will still go out when the driver fails. Some of
Tool-less access is still an important part of
the better LED drivers on the market today
good luminaire design, but equally if not more
have a life expectancy of 100,000 hours, if
important is a good IP rating. Because LEDs
engineered into the luminaire in a way that
are expected to stand on their own for such a
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THE AUTHOR
Paul Mitchell, Member IES (2004),
is a regional sales vice president
for Sternberg Lighting and heads up
their national education program.
He has been involved with street
and area lighting for over 15 years, and serves on both
the IES Roadway Lighting Committee and the IES
Street and Area Lighting Committee.
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2/6/13 6:11 AM