This example shows the energy–related dollar savings based on reduced energy consumption from retrofitting an existing lighting system that has F40T12 lamps and magnetic ballasts. In addition to using F32T8 lamps and electronic ballasts, the replacement system uses high power factor ballasts so fewer lamps produce the same light.

Old Lighting System The old lighting system had of 100 three–lamp fixtures. The lamps are 4–foot F40T12 bulbs powered by standard magnetic ballast with a ballast factor of 0.88. This combination produces 6,844 lumens per fixture.

New Lighting System The new lighting system has of 100 two–lamp fixtures. The lamps are 4-foot, energy efficient F32T8 bulbs powered by a newer electronic ballast with a ballast factor of 1.29. This combination produces 6,618 lumens per fixture. When the new lamps are ready to be replaced, their light output will be 3.3 percent less than the output of the old lamps at the end of their life.

Typical T12 (old) lamps have color rendition indices (CRIs) of less than 70. The T8 (new) lamps have CRIs of 80 or more. If starting lighting levels are adequate, the higher CRI of the T8 lamps will more than offset the 3 percent reduction in light output at the end of their life. The electronic ballasts of the new lamps will eliminate the annoying 60–cycle hum and strob of the old magnetic ballasts.

1. Compute the demand of your lighting systems using the following formula: (Watts per Fixture)(Number of Fixtures) =
   Demand in kW Watts 1,000 Example Existing System New System (140)(100) (56)(100) = 14 kW = 5.6 kW 1,000 1,000
2. Compute the demand savings with the following formula:
   Exisiting Demand – New Demand = Demand Savings
   14 kW – 5.6 kW = 8.4 kW

1. Compute energy use of your lighting system using the following formula: (Watts per Fixture)(Number of Fixtures)(Operating Hours per Year)/1,000 Energy use per year (in kilowatt-hours)
   Existing System New System (140)(100)(2,600) (56)(100)(2,600) = 36,400 kWh = 14,560 kWh


2. Compute the energy savings using the following formula:
   Existing Energy Use – New Energy Use = Energy Savings
   Example
   36,400 – 14,560 = 21,840 kWh per year energy savings

The electric bill of most facilities consists of two major charges, demand or kilowatts (kW) and energy or kilowatt–hours (kWh). The most accurate method of calculating electric energy–related savings is to take the charges from the electric bill. The average cost per kilowatt–hour will not always give accurate results. The Tech Tip, Saving Money by Understanding Demands Charges on Your Electric Bill (0071–2373–MTDC), explains demand charges. The rates used to calculate the electrical dollar savings came from the October 1999 bill for Fort Missoula, Building No.1, MTDC's office.

1. Compute your demand dollar savings using the following formula:
   ($/kW Charge1 + $/kW Charge2 + …from rate schedule)(Demand Savings per month)(12 months per year) = Demand Dollar Savings per Year
   ($4.944/kW + $2.425/kW)(8.4 kW per month)(12 months per year) = $742 per year dollar demand savings
   
   
2. Compute your energy use dollar savings using the following formula:
   ($/kWh Charge 1 + $/kWh Charge 2 +...from rate schedule)(Energy Savings) = Energy Dollar Savings per Year
   ($0.0039/kWh + $0.0289/kWh) (21,840 kWh) = $717 per year energy savings

Retrofitting an existing lighting system that uses F40T12 lamps and magnetic ballasts with F32T8 lamps and electronic ballasts can generate significant annual savings.