Glacier Site Lighting AnalysisJames M. eStandard (2� Associates, Inc.
CONSULTING ENGINEERS
WASHINGTON PLAZA • 300 WASHINGTON STREET • SUITE 206 • MONROE, LOUISIANA 71201 • (318) 322-0551 • FAX (318) 361-0517
August 13, 2007
Mr. Ian Macaskill, AIA
ARCHITECTURE +
300 Washington St., Suite 400
Monroe, LA 71201
RE: Site Lighting
Glacier Town Center
Kalispell, Montana
Dear Ian:
We have completed the illumination analysis of two site lighting layouts covering one-half of the
site at the referenced project. Our analysis utilized identical cut-off luminaires, lamps and ground
reflectance. Only the luminaire mounting height was changed. One layout utilized 25 foot poles
while the other layout utilized 40 foot poles. Only half the site was investigated in our lighting
analysis since nothing would be gained by completing the entire site. Asphalt paving of the parking
area was assumed, and having a light reflectance of 20 percent.
In order to show quantitatively the amount of light entering into the night sky, an imaginary
horizontal reference plane was inserted into our luminance calculations at a height of 100 feet
above the parking surface. Therefore, light leaving luminaires will travel downward at all angles
below 90 degrees and then reflect off the asphalt back up into the sky, and land on the imaginary
plane. Footcandles of lighting has been computed on the underside of the imaginary plane.
The analysis of the two afore mentioned schemes of site lighting follow:
SCHEME 1: 1000 watt metal halide luminaires atop 25 foot poles.
No. of Poles
= 64
No. of Luminaires
= 114
Total Lamp Lumens
= 12,540,000
Maximum Footcandle "Hot Spot" on ground
= 14.4
Footcandles on underside of imaginary plane
= 1.3
Total Watts of Electricity Used
= 114 KW
Total Lighting Material Cost
= $91,500.00
SCHEME 2: 1000 watt metal halide luminaires atop 40 foot poles.
No. of Poles
= 36
No. of Luminaires
= 73
Total Lamp Lumens
= 8,030,000
Maximum Footcandle "Hot Spot" on ground
= 8.5
Footcandles on underside of imaginary plane
= 0.75
Total Watts of Electricity Used
= 73 KW
Total Lighting Material Cost
= $74,350.00
CONCLUSION:
By comparing the intensity of light being bounced back into the night sky, it is evident that 1000
watt luminaires mounted on 25 foot poles doubles the footcandles of light at the 100 foot high
imaginary horizontal plane. Therefore, to reduce "sky -glow", it would be better to utilize a higher
luminaire mounting height.
If you or your client have questions or comments regarding the above site lighting analysis, please
contact me at your convenience.
Very truly yours,
Standmes M. _.
JMS, III/csm
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