Light Loss Factor (LLF) = Ballast Factor x Fixture Ambient Temperature Factor x Supply Voltage Variation Factor x Lamp Position Factor x Optical Factor x Fixture Surface Depreciation Factor x Lamp Burnouts Factor x Lamp Lumen Depreciation Factor x Fixture Dirt Depreciation Factor x Room Surface Dirt Depreciation Factor Required Light Output/Fixture (Lumens) = (Maintained Illumination in Footcandles x Area in Square Feet) Г· (Number of Fixtures x Coefficient of Utilization x Ballast Factor x Light Loss Factor) of Fixtures x Coefficient of Utilization x Light Loss Factor) Г· Area in Square FeetДЄverage Maintained Illumination (Footcandles) = (Total Lamps x Lumens/Lamp x Coefficient of Utilization x Light Loss Factor) Г· Area in Square FeetДЄverage Maintained Illumination (Footcandles) = (Lamps in One Fixture x Lumens/Lamp x Coefficient of Utilization x Light Loss Factor) Г· Area in Square Feet/Fixture Lumen Method L = Distance between that point and the point where light level is being calculatedД = Square Root of (H2 + L2) or D2 = H2 + L2Д¬alculating Average Light Level Throughout a Space (three formulas)ДЄverage Maintained Illumination (Footcandles) = (Lamps/Fixture x Lumens/Lamp x No. H = Distance between the lamp and the point direct below on the workplane Vertical Footcandles (fcv) = (I Г· D2) x L Horizontal Footcandles (fch) = (I Г· D2) x H For tilted-horizontal or vertical planes: In these cases, we often must determine light levels on workplanes that are not horizontal and perpendicular but tilted or even vertical. Many workplanes are not perpendicular to the direction of light intensity, which is why calculating light level at a point is useful for such applications.

Lux = Total Lumens Г· Area in Square MetersДЇor planes perpendicular to the direction of candlepower (Inverse Square Law):Д = Direct distance between the lamp and the point where light level is calculated Simple Return on Investment (%) = x 100ДЇootcandles (fc) = Total Lumens (lm) Г· Area in Square Feet Simple Payback on an Investment (Years) = Net Installation Cost ($) Г· Annual Energy Savings ($)ДҐ-Year Cash Flow ($) = 5 Years - Payback (Years) x Annual Energy Savings ($) Voltage (V) = Current in Amperes (A) x Impedance (Ohms) ECONOMIC FORMULAS Watts (W) = Volts (V) x Current in Amperes (A) x Power Factor (PF)

Unit Power Density (W/sq.ft.) = Total System Input Wattage (W) Г· Total Area (Square Feet) Lighting System Efficacy (Lumens per Watt or LPW) = System Lumen Output Г· Input Wattage Hours of Operation/Year = Operating Hours/Day x Operating Days/Week x Operating Weeks/Year

Demand for Power (kW) = System Input Wattage (W) Г· 1,000Д®nergy Consumption (kWh) = System Input Wattage (kW) x Hours of Operation/Year

Light intensity equation