Saving Street Lighting Energy & Maintenance Costs
Jack I. J'maev
A. Brooke Jones
ReadyTrace, Inc.
February 1, 2012
A new technology Street Light Dimmer (SLD) is now available. The new "stepless"
dimmer can save 40% or more in electricity costs and pays for itself in about 2 years.
The VariLuxTM SLD can be installed in 5 minutes (YES - 5 minutes) and there are no
additional fees beyond the purchase price . The energy savings potential has been
demonstrated in Santa Fe Springs, CA and a report of this initial test can be found at
Today, as cities across the country try to reconcile the need to maintain night-time safety
and the cost of public lighting, new and emerging technologies may hold the solutions.
Given that 30% to 40% (or more) of a city's electricity costs are directed toward street
lighting, it is no wonder that a fresh look at the entire realm of street light savings
technology is so vital. The VariLux device is so affordable, when compared to other
technologies, that cities can immediately start saving money on electricity and street light
maintenance. Reduction in energy usages also helps cities lower their carbon footprint.
Street Light Dimming
Dimming street lights is highly effective because the human eye has an extremely large
sensitivity range in low level light. In fact, it is hard to perceive the difference between a
street light operating at full power and a street light that has been dimmed down by 40%.
In Europe, street light dimming is widely applied and is considered the cost effective
alternative for saving 40% to 50% on electricity. If that is not enough incentive, the
savings created by the VariLux Street Light Dimmer can be realized within a 2 year payback period. The nearest competition, LED streetlights, take almost 10 years to pay for
themselves. This means that, after just 2 years, cities can start putting money in the bank.
If this sounds like sales hype, well it is - but it is driven by the excitement we have for
this new technology.
We can thank the Europeans for their extensive study efforts with respect to street light
dimming. In fact, the European studies have resulted in new standards and specifications
for intelligent street light control. These new concepts for street lighting are all predicated
on the concept of "stepless" dimming of street lights. There is a great deal of useful
information at "". Bottom line, street light dimming works and is
a viable option for saving electricity.
Additional equipment for programming is necessary, but the costs for such equipment are nominal.
Nominal signaling fees may be incurred when a city wants to use custom dimming profiles.
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VariLux Street Light Dimmer
Stepless dimming technology for High Pressure Sodium (HPS) lighting is not a new
concept. Using older technology, it takes several hours to install a dimming ballast
because the entire light fixture needs to be rewired. Even more time is needed to install
and establish the control system that enables cities to specify dimming profiles. Today,
all that has changed because the VariLux Street Light Dimmer (SLD) is a "plug-n-play"
replacement for the photo controls used on most street lights in the United States. Again,
it takes only 5 minutes to install a VariLux Street Light Dimmer.
People in cities around the world, especially in more progressive societies, share similar
life styles. In our modern society, street lighting is absolutely essential in order to
promote safe, night-time passage along arterial highways, collector roads and in
residential neighborhoods. The common factor here is that the amount of light needed is
a function of how many people are out and about. And, this can vary from city to city
and within different sections of a city. Without a doubt, street lighting separates us from
the "dark ages" and promotes general safety and discourages criminal activity.
American Ingenuity
It's a bitter pill, but cities all across the United States are suffering significant financial
crisis. In order to reduce electricity usage costs, many cities are actually resorting to
turning off selected street lights, for example every other street light. This, of course, is
not in the public's best interest. The new VariLux Street Light Dimmer (SLD) installs
in 5 minutes and can save cities 40% or more in street light electricity costs. And, the
VariLux device helps to extend the life of HPS street light bulbs. This means that the
cost of the VariLux SLD is generally recouped by avoiding the labor cost needed to
replace just one light bulb.
If we consider the lifestyle of our progressive population, it is easy to see that street lights
can be operated according to a pre-established dimming profile. For example, the graph
(Fig. 1) below shows how one city may choose to dim street lights in an industrial region.
As this graph shows, a particular city may choose to turn street lights "FULL ON" at
dusk, reduce power to 55% at 9 PM, increase power to 70% at 4 AM and then return to
"FULL ON" operation from 5 AM until dawn. Notice that we don't refer to 100%
power. This is because the VariLux SLD uses a technique called "depletion curve
tracking", which is described later in this paper. Of course, different areas in the city can
be programmed with different dimming profiles. This, too, is described later.
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VariLux Street Light Dimmer
Fig. 1 - Typical Dimming Profile
Value Proposition
The VariLux Street Light Dimmer pays for itself in about 2 years. Before VariLux, cities
had no cost effective way to reduce street light energy usage. Recently, LED street
lighting has been installed in many cities, but these installations have only been made
possible through Federal and private grants, rebate incentives and special loan programs.
Any way you look at it, the cost of LED street lighting is so high that a typical LED street
light will only pay for itself after 9 or 10 years.
Cities can now choose from three alternative options. The first option is to just do nothing
or to turn off a portion of their existing street lights. The second option is to replace the
existing HPS street light fixtures with LED light fixtures. This is a costly proposition
both in terms of the procurement cost and in terms of the labor needed to replace the
fixture. Today, the attractive option is to replace the photocell controller installed on the
existing HPS light fixture with the VariLux SLD. Table 1 shows a comparison of energy
savings and total cost of operating street lights over a 10 year period. The numbers speak
for themselves. Life Cycle Cost (L.C.C.) over this ten-year period is reduced by over
40%. It is important to realize that this cost comparison has been produced on very
conservative values and is based on only 31% energy savings. Actual test data shows
that 35 % to 40% energy savings is easy to achieve.
The data in Table 1 is based on VariLux field test data and compares the VariLux
technology against LED street lights relative to existing HPS installations. This
comparison also considers non-biased studies that clearly demonstrate that the
"equivalent" LED street light fixture does not meet the requirements established in the
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VariLux Street Light Dimmer
American National Standards Institute (ANSI) / Illuminating Engineering Society of
North America (IESNA) RP-8-00 standard for roadway lighting. According to studies
performed in accordance with the RP-8-00 standard, manufacturer recommend
replacements for a given power level HPS street light simply don't get enough light on
the ground and fail to meet requirements for uniformity in street light illumination. as
such, the comparisons made here are based on using LED street lights that are actual
equivalents to their HPS counterparts at varying power levels. These studies are, along
with other significant information, identified in the bibliography section of this
Table 1 - 10 Year Operating Costs
100 W
150 W
200 W
250 W
31 %
31 %
31 %
31 %
44 %
42 %
41 %
40 %
2.3 YR
2.1 YR
1.9 YR
1.8 YR
43 %
43 %
43 %
43 %
-3 %
10.5 YR
10.0 YR
9.1 YR
11.0 YR
5 Minute Installation
As hard as it is to believe the VariLux SLD installs in 5 minutes. This is because the
VariLux SLD is pin-for-pin compatible with C.136 compliant photocell used to control
most street lights used in the United States. This reduces the amount of labor needed for
installation. Because of the low procurement cost of a VariLux SLD and the easy
installation, the overall cost of operating a street lighting can be reduced by 40% or more.
Fig. 2 - "5 Minutes" & VariLux Is There !!!
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VariLux Street Light Dimmer
In order to install the VariLux SLD, the first step is to remove the photocell from the light
fixture as shown in the photo below. This is depicted in Fig. 3.
Fig. 3 - Removal of Photo Cell Controller
After the photocell is removed, the VariLux Street Light Dimmer, with its C.136
compliant connector, installs directly on the street light. This is shown in Fig. 4.
Fig. 4 - Installing the VariLux SLD
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VariLux Street Light Dimmer
After the service technician has installed the VariLux Street Light Dimmer onto a street
light, the SLD needs to be programmed. The VariLux SLD needs some pretty basic
information in order to operate properly. This information is established during the
programming phase of the installation. Programming the VariLux SLD takes less than a
minute. Programming is accomplished using an inexpensive Initialization Unit (IU),
which is shown in Fig. 5.
Fig. 5. - Initialization Unit
The Initialization Unit loads each newly installed Street Light Dimmer with several
parameters including:
City Identifier
Neighborhood Identifier
Turn-On Offset
Turn-Off Offset
Dimming Profile Identifier
When the SLD begins operation, it uses the City Identifier and the Neighborhood
Identifier in order to receive custom dimming profiles for particular neighborhoods in a
given city. The SLD receives custom dimming profiles from the InfoMate Network,
which is described below.
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VariLux Street Light Dimmer
The InfoMate Network also transmits five different standard dimming profiles. These
Residential Dimming Profile
Retail/Commercial Dimming Profile
Industrial Dimming Profile
Recreational Dimming Profile
Major Roadway Dimming Profile
All of these standard dimming profiles are provided by the InfoMate Network at no
additional cost. This means that cities can use different dimming profiles for residential
areas of a city and retail/commercial sections of a city. Major thoroughfare and industrial
regions of a city need different dimming profiles as well. Lastly, parks and schools will
typically use the Recreational Dimming Profile. Again, all of these standard dimming
profiles are provided by the InfoMate Network at no additional cost to the city. The
Dimming Profile Identifier that is loaded into the SLD is used to select a particular
standard dimming profile from the list of standard dimming profiles listed above. The
Dimming Profile Identifier loaded into the SLD uses a dimming profile that is transmitted
by the InfoMate Network for the particular city and neighborhood in which the SLD is
Each day, the SLD receives the time of "civil sunset" and "civil sunrise" from the
InfoMate radio station that is servicing that particular Street Light Dimmer. The SLD
then turns on the street light based on the sunset time plus or minus the turn-on offset that
is programmed into the SLD by the Initialization Unit. Of course, the Street Light
Dimmer shuts off the street light based on the sunrise time, as received from the InfoMate
Network and adjusted by the pre-programmed turn-off offset. This alone helps to reduce
energy usage when compared to standard photo cell controllers. No longer will street
lights burn just because of a cloudy, overcast day.
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VariLux Street Light Dimmer
InfoMate Network
The InfoMate Network is a nationwide network of AM radio stations that broadcast the
data needed to control VariLux Street Light Dimmers all across the United States. There
are over 40 AM radio stations that broadcast this data. The InfoMate signal can be
received almost everywhere in the United States, as shown in Fig. 6. For more
information about the InfoMate Network, please visit "".
Fig. 6. - InfoMate Network Coverage
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VariLux Street Light Dimmer
Management Software
Let's face it, a city manager is concerned about one thing - saving money! The InfoMate
Network enables sophisticated control of all street lights in a city without the need to
maintain a sophisticated control center and the cost associated with it. All the city
manager needs is a PC running Windows , an Internet connection and the "VariLux
Manager" software package.
Determining the amount of energy saved using any dimming technology is a balancing
act. Some regions in a city need more light at night while others need less. The amount
of light needed in a particular section of a city may vary during the night. Different areas
in a city may have more powerful street lights than others. All of these factors must be
considered before a dimming strategy is approved.
VariLux Street Light Dimmers are controlled by AM Radio, which communicates sunset
and sunrise times on a daily basis. Standard and custom dimming profiles are delivered
in the same way. Custom dimming profiles can be used by cities in order to maximize
their energy savings. The energy balancing described above, if done by hand, it would
take a city manager hours, days or maybe even weeks of effort to determine just how to
balance the lighting requirements across even a moderate sized city.
VariLux is supported by a sophisticated street light management software package called
"VariLux Manager". Free to cities and other government users, the VariLux Manager
interacts with the Initialization Unit, shown in Fig. 5, in order to build a database that
represents the number of street lights and their respective power ratings within the city.
The VariLux Manager software package uses this database to calculate energy savings
potential. This allows the city manager to try different dimming profiles across different
areas in the city in order to determine the best energy savings strategy. After the city
manager is satisfied with the custom dimming strategy for the entire city, the dimming
strategy is uploaded to the InfoMate Network, after which it is communicated by AM
radio to the Street Light Dimmers.
Fig. 7 shows how the graphical interface provided by the VariLux Manager software
package lets users create custom dimming profiles. This graphical interface is called the
"Dimming Profile" screen. New dimming profiles can be added using an intuitive
Windows interface. Various dimming profiles can be specified for monthly or quarterly
delivery to the Street Light Dimmers in the city. Each custom dimming profile can be
assigned a "turn-on" offset and a "turn-off" offset. During the night, the dimming level
can be adjusted for up to four different user-specified time intervals. Another important
feature is that each dimming profile can have different specifications for Friday and
Saturday nights. This helps promote safety over the weekend when more people are out
and about in the evening hours. For special events, when people are likely to be out late
at night, an "Event Profile" can be activated. The Event Profile is useful at sporting
stadiums, concert venues, parade routes and the like.
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VariLux Street Light Dimmer
Fig. 7 - Dimming Profile Interface
Once various custom dimming profiles are defined by the city manager, these custom
dimming profiles can be applied to different neighborhoods and sections of the city.
Fig. 8 shows the graphical interface provided by the VariLux Manager for assigning
different dimming profiles to different regions of the city. Because the VariLux Manager
receives street light information from the Initialization Unit, the VariLux Manager knows
how many street lights are in each region of the city and how much power they consume.
The VariLux Manager lets the city manager partition the city into different zones. For
example, there may be several residential zones, one or two commercial zones, and zones
for industrial areas and recreational centers. Once these zones are established in the Zone
Manager Interface provided by the VariLux Manager, each zone can be assigned to a
different dimming profile. Again, because the VariLux Manager knows how many street
lights are in each zone and the power rating of each of those street lights, the VariLux
Manager is able to estimate a total power savings for the city. Once a dimming strategy
for the entire city is deemed acceptable, then the city manager can upload the entire
dimming strategy to the InfoMate Network. No additional effort is needed.
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VariLux Street Light Dimmer
Fig. 8 - Zone Manager Interface
Emergency Override
Life is not without tragedy and there may be situations where dimmed street lights need
to be brought to 100% power levels. The VariLux Street Light Dimmer is equipped to
handle these emergency situations. As shown in Fig. 9, the Street Light Dimmer is
normally controlled by way of AM radio stations that are part of the InfoMate Network.
However, there may be emergency situations that require all dimmed lights to be brought
to 100% power. This can be accomplished by way of direct city control using a local
control system.
There may also be situations where street lights in the immediate vicinity of a crime
scene need to be shut off. For these types of police emergencies, as depicted in Fig. 9, a
remote control can be used to force street lights to a 100% power level or to turn off the
street lights within a particular radius of the police officer. A police officer can restore
street lights to 100% power or turn off street lights within 100 yards or 300 yards.
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VariLux Street Light Dimmer
Fig. 9 - Emergency Local Override
The local override feature requires additional equipment, which can be installed at the
city maintenance yard or at city hall or at other strategic locations within the city. The
local override system can be useful in situations of urban stress.
What About LEDs ???
The most modern and most misunderstood street light technology is Light Emitting
Diode (LED). LED street lights have been studies for years and some cities have adopted
the technology. Most LED projects have only been implemented through long-term
loans and with the support of Federal Grants. Some projects, most notably in the City of
Los Angeles, have been co-sponsored by the Clinton Foundation.
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VariLux Street Light Dimmer
There is a great deal of debate about how effective LED street lights are, how they are
perceived by the public and their energy efficiency. The United States Department of
Energy (DOE) is administering a program (called the "GATEWAY Program") in order to
test the efficacy of this emerging technology. In numerous reports, the DOE Gateway
Program has attempted to rationalize the use of LEDs for street lighting.
The findings in many of there reports appear to be skewed in order to support the
expenditure of public monies for this technology. Thus far, the only un-biased reports are
those presented by the Lighting Research Center (LRC) at Rensselaer Polytechnic
University, Troy, NY. The LRC reports have come under attack by Government and
private institutions. In spite of these attacks, the LRC continues to maintain it's position
that the cost associated with LED street lights is more than twice as much when
compared to HPS street lights. Amazingly, even after attacking the LRC studies, the DOE
admits that the pay-back-period for LED street lights is in the range of a decade (yes - 10
years) or more.
Bright Lights - Bright Glare
LED street lighting may be fashionable, but many cities are now discovering that the
harsh white light provided by LED street lights is far from desirable. HPS lighting, with
it yellow-orange glow, closely mimics moonlight. Tens of thousands of years of
evolution have caused our human eyes to adjust to this type of "moonlight" for night
vision. The bright, bluish-white light generated by LED street lights is just not what we
are comfortable with at night.
To understand the problem, it is important to appreciate how LED street lights generate
"white light". When we look at the white light coming from an LED street light, most
people immediately notice the "bluish tinge" that comes along for the ride. Although the
"bluish tinge" may not be all that of a problem, it does affect night vision and it interferes
with police night vision equipment. Both of which pose potential public safety issues.
The critical issues here is that when a motorist moves from an area that is lit by LED
street lights back into an area that is lit by HPS lights, it takes time for the human eye to
readjust for night vision. This is not only uncomfortable, it is also hazardous as the eye
takes time to make this readjustment. Another factor is that, because LED street lights
are a strong point-source of light, the eye is naturally drawn to the street light fixture
itself, rather than paying attention to the road. When considering that it takes higher
power LED street lights to illuminate the roadway, when compared to HPS lighting, the
discomfort glare and annoyance of LED street lighting can not be ignored.
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VariLux Street Light Dimmer
So, why do LED street lights create a "bluish tinge" ??? The technical reason for this not
that difficult to understand. As shown in Fig. 10 above, the most economical way to
create a white LED is to use a blue LED chip. The blue LED chip generates blue light,
which is filtered through a yellow phosphor. As the blue light moves through the yellow
phosphor, a portion is converted to green light and some is converted to red light. This
effect, known as the "Stokes Wavelength Shift", is depicted in Fig. 11.
Fig. 10 - White LED Structure
The combination of the remaining blue light with the red and green light creates a white
light. The problem is that the amount of green and red light can not be accurately
controlled and any remnant blue light creates the "bluish tinge" that we see in LED street
lights today. To make matters worse, this color changing effect, i.e. the Stokes Shift, is
inherently inefficient and generates a great deal of heat. This heat eventually causes the
phosphor to deteriorate resulting in a street light that will emit more and more blue light
as it ages.
One of the greatest challenges in the design of LED street light fixtures is to shed the heat
generated by the Stokes Shift. The heat generated by the blue LED chip also needs to be
dissipated. All of this heat is wasted energy and if it is not dissipated correctly, the
phosphor will degenerate over time and more blue light will be created by the LED light
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VariLux Street Light Dimmer
Fig. 11 - Stokes Wavelength Shift Effect
Many research projects are under way to help improve white LED manufacturing
techniques in order to obtain a more pure white light, but for now, this remains the most
economical method for producing the white LEDs that are used in street lights today.
So, for the time being, the "bluish tinge" remains.
LED Light Coverage
When LED lighting is used to replace High Pressure Sodium (HPS) lamps, it can be done
in two ways:
Existing lamp poles can be used to mount the new LED street lights
New lamp poles with the LED street lights can be placed at closer intervals
The first method provides insufficient light between the poles when manufacturer
"equivalent" LED street lights are used. This means that, in order to have an equivalent
amount of light on the ground, brighter (and thus more expensive and power-hungry)
LED street lights must be used. The second method of spacing the poles closer together is
only economically effective for new construction. Despite the claims made by their
manufacturers, the "equivalent" LED street lights are simply not direct replacements for
their HPS counterparts. This problem is depicted in Fig. 12.
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VariLux Street Light Dimmer
This problem of insufficient light levels can only be addressed by increasing the power of
the LED street lights or by moving the street lights closer to each other. Given that the
latter solution is not economically feasible for retrofit applications, this drives the need to
use higher powered LED street light fixtures. This, of course, increases the original
procurement cost of the LED light fixtures and increases the power consumption. All of
these factors are considered in the Value Proposition presented earlier in this paper.
Fig. 12 - LED Street Light Spacing
Depletion Curve
When an HPS light bulb is installed, it typically produces about 40% more light than it
does when it reaches the end of its life. Fig. 13 presents a typical depletion curve for a
High Pressure Sodium light bulb. Because a brand new HPS light bulb produces much
more light than what is actually needed, the VariLux Street Light Dimmer immediately
takes advantage of this fact by reducing the power level of the street light in order to
conserve energy.
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VariLux Street Light Dimmer
Earlier, we referred to a "FULL ON" power level. The FULL ON power level varies
based on the age of the HPS bulb. The VariLux SLD tracks the age of the HPS bulb and
uses a well established depletion (a.k.a. depreciation) curve in order to determine the
amount of power needed to comply with the requirements of "FULL ON".
Considering just a couple of examples from Fig. 13, the first 1,000 hours of bulb life
requires only 68% power in order to deliver the requisite 65% of bulb output, which is
the minimum required for roadway lighting at the end of a 20,000 hour bulb life. As the
HPS bulb continues to age, the VariLux Street Light Dimmer applies more power to the
bulb in order to meet the 65% end-of-life target bulb output. So, even after the HPS bulb
as served an equivalent 10,000 hours, the power applied to the street light fixture is 86%
of the true 100% full on power. This is an immediate savings that contributes to lower
energy consumption and reduced life cycle cost.
Fig. 13. - HPS Depletion Curve
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VariLux Street Light Dimmer
1. National Lighting Product Information Program (NLPIP), “Streetlights for Collector
Roads”, Volume 13 Number 1, September 2010 (Rev. 2, November 2010)
2. Response sent by Pacific Northwest National Laboratory to the NLPIP regarding the
Gateway Program, October 13, 2010.
3. Response to Correspondence Sent by the Pacific Northwest National Laboratory to
the NLPIP Regarding Specifier Reports: Streetlights for Collector Roads, October
29, 2010
4. Response to Postings: From the Desk of Jim Broderick Regarding Specifier Reports:
Streetlights for Collector Roads, November 15, 2010
5. NLPIP Releases Addendum to Street Lighting Report, 7 January 2011, (USA)
Additions to Street Lighting Technologies research addresses industry criticism of
report that states LED streetlights are not as efficient as HPS streetlights
6. Final Report prepared in support of the U.S. DOE Solid-State Lighting Technology
Demonstration GATEWAY Program, December 2011
7. LED Roadway Lighting: Palo Alto Residential and Commercial Streets, DOE
Building Technologies Program
8. Visibility, Environmental, and Astronomical Issues Associated with Blue-Rich White
Outdoor Lighting, May 4, 2010, The International Dark Sky Association
9. Intelligent Road and Street Lighting in Europe (E-Street), 30 Jun 2008, Sofia
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VariLux Street Light Dimmer
10. PG&E Emerging Technology Program, Application Assessment Report #0714, LED
Street Lighting, Oakland, CA, January 2008
11. NLPIP Volume 11, Issue 2, “Dynamic Outdoor Lighting”, September 2010
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