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.
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 SolidState 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.
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.
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.
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.
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 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)  


Calculated Lifecycle 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. 