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The Super Light – Can an LED Save A City?

March 19, 2010

With the economic flat tire we’re running on, we like to think our various government agencies use all the tax money they collect in responsible ways.  The daily federal arguments on spending fill the nightly news with examples that prove this wish wrong and always seem stupidly complex.  Local governments face similar problems but scaled down.  Perhaps local governments are the place to start implementing solutions, as there is even more to paying for common services, like traffic lights, than meets the eye.

Unfortunately, something as simple as traffic lights takes on complexity when viewed at a city or county-wide level.  Everything from availability of replacement bulbs to scheduling maintenance with boom-trucks comes into play.  Of course, when we add cost to the mix, the complexity grows by leaps and bounds.  In the end, cost is the part we, the citizens, are really interested in, being that money out of our pockets pays for it.

The prototypical traffic light uses three halogen light bulbs around 150 watts each, with one of the lights on at all times.  At a standard intersection, there are at least four traffic lights, one for each direction, with many intersections having a good number more.  As cost is our primary concern, let’s put some numbers to it.  In South Carolina; our average cost per kilowatt in 2009 was $0.0553 (Source: U.S. Energy Information Administration (Dec 2009)) .  That means a single 150 watt bulb running continually costs about 20 cents a day.  With each intersection having at least four, that’s 80 cents per day per intersection.  Here is a quick table showing various costs:

Lights per
intersection
Daily Monthly Yearly
4 $     0.80 $   23.89 $   290.66
8 $     1.59 $   47.78 $   581.31
12 $     2.39 $   71.67 $   871.97
16 $     3.19 $   95.56 $1,162.63

Extending the figure out for various numbers of intersections:

Number of
Intersections
Daily Monthly Yearly
100 $      79.63 $    2,388.96 $     29,065.68
500 $     597.24 $  17,917.20 $   217,992.60
1000 $  1,592.64 $  47,779.20 $   581,313.60
5000 $11,944.80 $358,344.00 $4,359,852.00

This is only the cost of electricity.  The average life of a halogen bulb is just over 2,000 hours or less than 90 days meaning each light is replace three or four times a year.  Simply to provide traffic lights, city and county governments face substantial costs.  This is where the LED comes in.

LED stands for Light Emitting Diode.  We have all seen the little red lights on various types of electronic equipment.  Most are LEDs.  While the theory of their use has been around for over 100 years, true practical applications were not developed until the 1970s.  Even then, LEDs lack the intensity for use beyond indication lighting (i.e. showing a status as on or off).  Over the last thirty years, changes in LEDs allow for bright lights in every color of the spectrum.

The LED has many advantages over the incandescent, halogen, and Compact Florescent Light (CFL) style systems.  They use only a fraction of the electricity and last for years, if not decades and they do not have the mercury found in CFLs.  Cities across America are in the process of changing their traffic lights to LED based units.  To produce the same amount of light, as a 150 watt halogen traffic light, requires only 15 watts of LED powered lighting.  Using the same data above:

Lights per
intersection

Daily Monthly Yearly
4 $  0.08 $ 2.39 $ 29.07
8 $ 0.16 $ 4.78 $ 58.13
12 $ 0.24 $ 7.17 $ 87.20
16 $ 0.32 $ 9.56 $ 116.26

Again, extending the figures for number of intersections:

Number of Intersections

Daily Monthly Yearly
100 $ 7.96 $ 238.90 $ 2,906.57
500 $ 59.72 $ 1,791.72 $ 21,799.26
1000 $ 159.26 $ 4,777.92 $ 58,131.36
5000 $1,194.48 $ 35,834.40 $ 435,985.20

Producing a savings over halogen bases lighting of:

Number of Intersections

Daily Monthly Yearly
100 $      71.67 $    2,150.06 $     26,159.11
500 $     537.52 $  16,125.48 $   196,193.34
1000 $  1,433.38 $  43,001.28 $   523,182.24
5000 $10,750.32 $322,509.60 $3,923,866.80

These costs only reflect a saving in the electricity.  A halogen light costs around $5.00, for 100 intersections with six lights that works out to $12,000 a year just in bulbs.  Of course, the cost of labor to replace bulbs is saved too.

Thankfully, most cities have all ready replaced or are currently replacing their traffic lights.  The question is what other areas are there to save money.  It must be remembered, when we are talking about a city or county, it is never one light bulb, it’s thousands.  It’s not the 1 cent for a sheet of paper but the $10,000 for a million sheets that becomes an issue.

It is obvious that replacing traffic lights produces savings.  It is one of many examples where savings are found.  Others are less obvious; perhaps reducing the requirements of a procedure or even rethinking the way student report cards are sent to parents will produce savings.  Maybe they won’t, the point is we will not know until we look.  We need to examine everything to ensure the service is in tune with the times and is provided in the most cost-effective manner.

In the end, the LED will not save a city but is simply an example of the type of thinking that will save it.  Every expenditure, to serve the public good, must be questioned.  No one questions the need for traffic lights, but can and do question the cost.  By seeking a less expensive option, local governments are saving real dollars, real tax dollars we do not have to pay.

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3 comments

  1. Note: the 0.0553 rate applies to industrial customers, I do not for sure that is the rate municipalities receive but I hope the utilities give them a break.


  2. Nice example, well written.


    • Thanks Suzie, It is really one are where local governments should get credit for forward thinking. Often, it is easier to beat them up on the bad things



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