22 August 2006
Shadows: Locate and space poles so that the light from the luminaires
minimizes shadows that could conceal potential hazards.
Vertical Illuminance: Vertical illuminance lights individuals' faces as well
as potential hazards.
Target Horizontal Illuminance: Follow the Recommended Maintained
Illuminance Values for Parking Lots outlined in IESNA RP-20-98.
Nighttime use areas such as retail and libraries should use the higher
"Enhanced Security" values. Facilities that are primarily daytime use only
such as offices should use the "Basic" values. Average illuminance levels
are typically 10 -20 lux (1-2 fc) although maintaining the minimum,
maximum, and uniformity criteria is more important than meeting an
Parking lot lighting should provide uniform illuminance or luminance while avoiding
direct glare. By utilizing fully shielded or full cut-off luminaires, the direct beam light that
contributes to light pollution will be eliminated. Because poles are often located at the
perimeter of lots and next to adjacent properties, light trespass must be carefully
considered and prevented. Cut-off luminaires, house-side shields, and low wattage
lamps all help to reduce the chance of light trespass.
RULES OF THUMB:
Spacing to Mounting Height: When beginning a design, start with a 4:1
spacing to mounting height ratio and modify accordingly to meet critical
Distribution: Use Type V distributions for luminaires within the parking
areas. Use Type III and IV distributions for luminaires along the
EXAMPLE ANALYSIS WITH LUMEN EFFECTIVENESS MULTIPLIERS:
This parking area example shows how lumen effectiveness multipliers may be used to
compare high-pressure sodium and metal halide sources. A 200 x 600 ft parking lot
was evaluated with the AGI lighting calculation program (Lighting Analysts, Inc.). The
table on the following page outlines the results for two different light sources with the
same pole layout, luminaire, and mounting height. The lamp wattages are the same
(250 watt) for each case.
Determining Effective Values
Step #1: Calculate Luminance. The first line for each case shows the
calculated average, maximum, and minimum luminance. These are
determined from a lighting calculation program such as AGI.
Step #2: Determine LEM Multipliers. The luminance values were then
applied to Table 2-1 or Figure 2-7, "Lumen Effectiveness Multipliers"
shown in Chapter 2 "Lighting Design Considerations". By entering the first
row of Table 2-1 with any luminance value, a corresponding effectiveness
multiplier can be read or interpolated for three different types of light