d

  current page:
    Lighting Practices>
      Articles & Studies>
        Chicago: A Case Study

May, 2008

Chicago: A Lighting Case Study

To explore real-world examples of outdoor lighting techniques, their effectiveness, and their costs, we present here an analysis of the street lighting operated by the City of Chicago. While Chicago is Illinois' largest city, it by no means is home to all of the state's outdoor lighting; the data shown below would be similar for many other municipalities (scaled to population size and area).

The City operates a number of different styles of streetlight fixtures, installed over several decades of time; some of the more common types will be looked at in more depth. This study only includes streetlights operated by the City; it does not tally those on private property (parking lots, buildings), nor those operated by the Illinois Department Of Transportation (state and federal roads/highways). Figures on the total numbers of each type of lighting which the City operates were supplied by the Chicago Department of Streets & Sanitation, Bureau of Electricity, November, 2007.
 

"TORCH"-STYLE STREETLIGHTS THROUGHOUT DOWNTOWN--
 
Chosen for their period appearance, these streetlights feature modern-day high-pressure sodium lamps. As noted on our Lighting Studies> Style & Fashion page, period fixtures which simply replace a gas flame or dim Edison lamp with a modern, tremendously brighter, high intensity discharge lamp are neither efficient energy users or good at keeping glare levels down.

The scale diagram below illustrates the standard installation of this fixture type along city streets in Chicago, with the 20' poles spaced 45' apart. Presumably they were installed to light the sidewalks and adjacent roadway and parking zones, illustrated by the lighter gray zone under the center pole. But, the glass globes on the dual fixtures on each pole allow the energy output of the lamps to shine out in a spherical shell from the pole tops. Only about 37% of the light actually goes where it is needed.
 

"Torch"-style street lamps as installed in downtown Chicago: While their energy/light output shines in all directions, just over a third of it goes to directly illuminate the sidewalks and street. An efficient, focused lamp fixture could provide the same level of illumination to the walkways and roadway while consuming less than half the energy, night after night, year after year.
 

COBRA-STYLE STREETLIGHTS THROUGHOUT THE CITY--
 
These traditional streetlight fixtures are used to illuminate many roadways and alleys. They vary in design; some newer ones have their lamps recessed in the fixture, with flat, horizontal glass shields underneath, sending most of their light downward to the street and sidewalks. The majority, though, feature a hanging globe diffuser/shield, sending much of their light output sideways rather than downward.
 
The fixtures in this photo are of the older type. A pattern has been added in green to delineate the area which just one of the lamps is intended to illuminate; obviously, much of that lamp's output is shining outside of that zone. Note how the direct glare from the fixtures way down the road is plainly visible; why should any of their direct energy output be seen from this spot? As in the case of the "torch" style fixtures above, lower wattage lamps in properly focused fixtures could provide the same roadway and sidewalk illumination as these wasteful streetlights; the reduced glare from such fixtures would actually improve visibility and safety.
 

Chicago Streetlight Facts & Figures

The table below lists the numbers of various types of streetlight being operated by the City of Chicago as of November, 2007; we've added up the total wattage of the fixtures, and totaled up some figures on energy consumption. As noted above, these figures do not include any of the outdoor lighting in the City other than that operated by the Department of Streets & Sanitation; other types include privately owned lighting (most parking lots and buildings), that operated by other City departments (parks, buildings, etc.), and that operated by the State of Illinois (highway lighting, etc.)
 

Fixture Type

Arterial 400W

Arterial 310W

Residential 250W

Residential, Pedestrian & Alley 150W

Alley 250W

Pedestrian 100W

Pedestrian 50W

Flood 400W

Total Number

17,560

68,342

21,478

78,107

58,632

2,730

7,892

892

Total Kilowatts¹

8,148

24,945

6,658

14,494

18,176

355

521

414

KWH Per Year²

34,497,955

105,616,410

28,190,734

61,366,631

76,956,845

1,502,647

2,205,372

1,752,402

Lumens Output³

790,200,000

2,255,286,000

579,906,000

1,124,740,800

1,583,064,000

23,341,500

28,411,200

40,140,000

¹ Wattage total includes lamp plus ballast for each high intensity discharge fixture.   ² Yearly kilowatt-hour total based on operating time of 4,234 hours per year. This is derived from the U.S. Naval Observatory's determination that Chicago experiences 4,417 hours between sunsets and sunrises each 365-day year, and subtracting 15 minutes past each sunset and before each sunrise for the period of twilight in which streetlights might not be turned on.  ³Lumens output is based on the mean output over the normal lifetime for each lamp type; initial light outputs are considerably higher.

 
TOTALING THE FIGURES
 
For all of the fixtures in the table above the totals are as follows:
- Number of fixtures: 255,633
- Total kilowatts of power draw: 73,710⁴
- Total kilowatt-hours of electricity consumed per year: 312,088,955
     which represents 267,086 tons of C0₂ production from electrical generation⁵
- Total light output: 6,425,089,500 lumens⁶ (yes, that's almost 6.5 billion lumens)
- Annual electricity cost for the City: $18,007,535⁷

IF THE LIGHTING FIXTURES IN USE NOW ARE 30% INEFFICIENT, that represents the waste of:
 
- 93,626,699 kilowatt-hours per year, or 80,126 tons of excess C0₂ production
- 1,927,526,850 lumens of light going where it isn't needed, every minute of every night of the year
- $5,402,261 in taxpayers' money will be spent on wasted power this year
 
And, as you can see from the illustrations on the upper portion of this page, 30% inefficiency is probably a gross underestimate!

⁴Total power draw, electricity consumed, light output and costs are computed assuming that all fixtures are operational, functioning within normal specifications, and only operating during nighttime hours    ⁵C0₂ equivalence computed from national average for electrical generation, per The U.S. EPA    ⁶For comparison, a 100W soft white incandescent light bulb puts out about 1,690 lumens    ⁷Calculated from a cost of $0.0577/kilowatt-hour, the average rate which the City paid Commonwealth Edison for electricity during the first 3 months of 2008, per the Department of Streets & Sanitation, May, 2008.

Millions Of Wasted Watts In One Snapshot

Chicagoland from space, daytime.

Chicagoland from space at night.

The photo on the right from the International Space Station (ca. 2003) shows not only some of the billions of stray, wasted lumens of light energy documented above, but also billions more from other irresponsible Chicago area outdoor lighting. This tidal wave of energy waste goes on hour after hour, night after night, year after year, and will do nothing but increase until reponsible lighting practices become the norm.

Return to Page Top

light pollution Illinois Chicago Cook County DuPage County Will County Springfield energy enviromnent global warming anti light pollution legislation lighting ordinances