Green Light New Orleans is a 501c3
nonprofit organization
EIN 208151937
Calculations for energy savings
Assumptions:  
Energy Cost per KWH (March 2006, Entergy New Orleans)  $0.118 
Energy savings / bulb: One 15w light bulb used 24hrs/day for one year (8,760 hrs) saves 394.2 KWH (source: Entergy New Orleans lighting calculator)  $46 
Average daily use per light bulb:  3.5 hrs 
Average Lifetime for a CFL bulb= 10,000 hrs  >6 years 
Green Light New Orleans installs light bulbs with an average lifetime of >10,000 hrs and an average wattage of 15w. For our calculaion we discount the life time to 8760 hrs to account for early lamp failure.  
Calculations for CO2 emission reduction  
EPA recommends to use the value for the subgrid from the eGRID database. The value for the SERC Mississippi Valley subregion (our region) from the latest eGRID data (for the year 2004) is 1135 lb/MWh (1 MW = 1000 kW), which is equivalent to 0.515 kg CO2/kWh, the most widely used measure. 394 KWH = 447lb CO2  
The international reporting standard for CO2 emissions is in metric tons. Since there are 2204.62 lbs per metric tonne, a single ton of carbon dioxide equates to 2204.62 pounds of CO2. Our main focus is environmental. The savings posted on sections of this web site are on purpose a low estimate (We install bulbswith an average 10,000 hr life time but we only calculate 8,760 hrs). The savings might be higher than stated on the web site. Thank you for your support! 

1 CFL = savings of 394KWH = $46 = 447 lb of CO2 
Calculations for rainwater retention
Assumptions:  
Average roof square footage:  1300 
Amount of downspouts:  4 
Amount of water diverted in percent:  85 
Capacity of rain barrel in gallons:  50 
NOOAA Airport daily rainfall report  
Calculations for water retention  
See detailed explanations  
See rainfall data  
See financial calculations  
2255.1 Gallons of water / rain barrel / year = $50  
Our methodology discounts the impact according to survey results to the following question: 