Electrical Formulas
Demand for Power (kW) = System Input Wattage (W) ÷ 1,000
Energy Consumption (kWh) = System Input Wattage (kW) x Hours of Operation/Year
Hours of Operation/Year = Operating Hours/Day x Operating Days/Week x Operating Weeks/Year
Lighting System Efficacy (Lumens per Watt or LPW) = System Lumen Output ÷ Input Wattage
Unit Power Density (W/sq.ft.) = Total System Input Wattage (W) ÷ Total Area (Square Feet)
Watts (W) = Volts (V) x Current in Amperes (A) x Power Factor (PF)
Voltage (V) = Current in Amperes (A) x Impedance (Ohms) [Ohm's Law]
Economic Formulas
Simple Payback on an Investment (Years) = Net Installation Cost ($) ÷ Annual Energy Savings ($)
5-Year Cash Flow ($) = 5 Years - Payback (Years) x Annual Energy Savings ($)
Simple Return on Investment (%) = [Annual Energy Savings ($) ÷ Net Installation Cost ($)] x 100
Design Formulas
Footcandles (fc) = Total Lumens (lm) ÷ Area in Square Feet
1 Lux (lx) = 1 Footcandle (fc) x 10.76
Lux = Total Lumens ÷ Area in Square Meters