Calc lumen ohm7/9/2023 ![]() ![]() H = Distance between the lamp and the point direct below on the workplane ![]() Vertical Footcandles (fcv) = (I ÷ D2) x L Horizontal Footcandles (fch) = (I ÷ 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 ÷ Area in Square Metersįor planes perpendicular to the direction of candlepower (Inverse Square Law):ĭ = Direct distance between the lamp and the point where light level is calculated Simple Return on Investment (%) = x 100įootcandles (fc) = Total Lumens (lm) ÷ Area in Square Feet Simple Payback on an Investment (Years) = Net Installation Cost ($) ÷ Annual Energy Savings ($)ĥ-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) ÷ Total Area (Square Feet) Lighting System Efficacy (Lumens per Watt or LPW) = System Lumen Output ÷ 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) ÷ 1,000Įnergy Consumption (kWh) = System Input Wattage (kW) x Hours of Operation/Year ![]()
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