ASSIST Recommends Parking Lot Luminaire Calculator

ASSIST program

This calculator is designed to estimate the Luminaire System Application Efficacy and overall cost of a given parking lot luminaire within a given task area, based upon the luminaire's IES distribution file and your other inputs.

Begin your calculations by Defining your luminaire


This calculator is based on ASSIST's recommendation for testing and evaluating the photometric performance of parking lot luminaires for all light source technologies. The recommendation was developed by the Lighting Research Center (LRC) at Rensselaer Polytechnic Institute in collaboration with members of the Alliance for Solid-State Illumination Systems and Technologies (ASSIST).

ASSIST's recommendation to determine the Luminaire System Application Efficacy of light sources for parking lot applications is based on the premise that luminaires should meet the target photometric criteria for parking lots with minimum energy usage. The two main design criteria for parking lots are a minimum light level and a certain uniformity ratio. Because luminaires are designed to meet the needs of different parking lot geometries, manufacturers assign distribution types that describe the coverage area of the luminaire and its shape. Thus, the Luminaire System Application Efficacy is based on a calculation area corresponding to the intended coverage for a given luminaire's distribution. The method accounts for the light (in lumens) that falls inside this target area, but only if the illuminance and uniformity criteria are met. You can download more information on this evaluation method: Vol. 7, Issue 3: ASSIST recommends: Recommendations for Evaluating Parking Lot Luminaires.

IES File Selection

Upload the IES file for your desired luminaire. If you don't have one, you can simply select an example IES file provided below.

The IES file format defines the distribution of light from a particular luminaire. They are provided by most major lighting manufacturers and can usually be downloaded, free of charge, from their respective websites.

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Light Distribution and Classification

Below is a summary of the photometric file you uploaded for evaluation. The file contains relative photometric data. The following fields affect the calculation of application efficacy. Please verify that the information is correct and make changes as needed.

Input Power

watts

Candela Multiplier

Distribution Type

Using the IES file you've specified, we've calculated the following IES luminaire distribution types. More information on Lateral and Vertical distribution types can be found on the ASSIST recommends site.

Lateral: Vertical:

Determining Optimum Pole Height

Next, we will determine the optimum pole height for your luminaire.

Illuminance Criteria

The minimum and maximum allowed illuminance values. Any illumination falling outside of this range will be considered wasteful and be penalized when calculating Luminaire System Application Efficacy.

fc to fc

Number of Luminaires per pole

Light Loss Factor

Light loss should be anticipated and taken into account for any design. Different sources provide guidance on how to estimate recoverable and non-recoverable light loss factors for outdoor systems. See for instance the IESNA Lighting Handbook, 9th Edition (Rea 2000).

Step 4 – Luminaire System Application Efficacy at Desired Pole Height

Once we've determined the optimal pole height, we can calculate the Luminaire System Application Efficacy at that pole height.

Simply put, the Luminaire System Application Efficacy is a measure of the amount of power (watts) needed to deliver the required amount of light (luminous flux) to the target area, and is therefore measured in lumens per watt. By maximizing this value, we maximize energy efficiency for the given design.

For details on how this calculation is performed, please review Vol. 7, Issue 3: ASSIST recommends: Recommendations for Evaluating Parking Lot Luminaires.

Desired Pole Height

Step 5 – Life-cycle Cost

To calculate the average and per-pole life-cycle cost, please provide the following information. We assume that the luminaires operate 365 days a year, and that the installation and replacement costs include both parts and labor.

  1. ($)
  2. ($)
  3. ($)
  4. (¢/kWh)
  5. %

Number of years for life cycle cost consideration

Step 6 – Light Level Adjustment for Different Light Sources

This step lets you calculate the reduction in illuminance (and therefore input power) that can be achieved by switching to an alternative light source with a higher S/P ratio.

To learn more about Light Level Adjustment for Different Light Sources view Vol. 6, Issue 2: ASSIST Recommends: Outdoor Lighting Visual Efficacy.

S/P ratio of the base case

Reflectance of the pavement in percent

S/P ratio of the alternative light source

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Summary of Calculations

IES file chosen  → 250W MH
Illuminance Criteria  → 0.2 fc to 4 fc
Luminaires per pole  → 1
Optimum Pole Height for Your Luminaire
Lateral distribution type  → Type III
Vertical distribution  → Medium
Light loss factor  → 1.0
Optimum pole height  → 15 feet (4.5 meters)
LSAE at optimum pole height at optimum pole height  → 15.4 lm/W
Luminaire System Application Efficacy in lm/W at different pole heights
Luminaire System Application Efficacy at Desired Pole Height
Desired pole height  → 15 feet (4.5 meters)
Luminaire System application efficacy  → 15.4 lm/W
Estimated longitudinal spacing  → 135 feet (41.1 meters)
Estimated transversal spacing  → 135 feet (41.1 meters)
Average illuminance in area  → 1.3 fc (13.9 lx)
Average power density  → 1.3 W/ft² (13.9 W/m²)
Illuminance on the Task Plane (Pavement)
Calculated Life-cycle Cost
Luminaire price  → $1,000
Initial installation cost per pole  → $500
Lamp life (hours)  → 10,000
Hours of operation per day  → 12
Lamp replacement cost  → $200
Electricity cost  → 10/kWh
Annual interest rate  → 5%
# of years to consider  → 30 years
Life cycle cost per pole  → $7,754
Average life cycle cost  → 63¢ / ft² (6.79 / m²)
Light Level Adjustment for Different Light Sources
S/P ratio of the base case  → 0.65
Reflectance of the pavement in percent  → 7%
S/P ratio of the alternative light source  → 2.15
Illuminance can be reduced to 0.8 fc (8.7 lx) which is 37.1% lower than the base case light source.
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