Floodlight Calculations:
Foot Candles, Mounting Height, Light Depreciation, and Number of Flood Lights Needed

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Use the following formula to calculate the required number of flood lights based on recommended foot candles, mounting height, and light depreciation.

Step 1: Determine the foot candle level (FC) from the recommended lighting foot candle table.

Step 2: Determine the total square footage (ft²) of the area to be lighted (length x width).

Step 3: Determine the type of fixture to be used and its proper mounting height.

Step 4: Identify the initial lumens (LM) of the fixture type.

Step 5: Determine the dirt depreciation factor of the fixture from the Light Depreciation Chart.

Step 6: Use the formula with your above data to calculate the number of fixtures. Round decimals to the nearest whole number.

Formula: Number of Fixtures = 3 x FC x ft² / (LM x Dirt Depreciation)

Example: Using a 400 watt High Pressure Sodium (HPS) on a 30 foot pole: 3 x 2 x 40,000 / (50,000 x 1.01) = 4.85 Round up the decimal. Number of Fixtures = 5

Note: This is not a precise lighting guide.

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