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

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.

Lighting Area Recommended Foot Candles
Storage Yards: Inactive 1
Railroad Yard Switch Points 2
Shipyards 5
General Building Construction 10
Corridors / Stairways / Restrooms 10‑20
Storage Rooms 10‑50
Storage Yards: Active 20
Loading Platforms 20
Conference Rooms 20‑50
Gymnasiums 30‑50
Merchandising 30‑150
Cafeterias 50
Classrooms 50‑75
General Offices 50‑100
Manufacturing Assembly 50‑100
Areas with Video Display Terminals (VDTs) 75
Drafting / Accounting 100‑200
Terminal Apron / Parking 0.5
Hanger Aprons 1
Light Surfaces 20‑50
Dark Surfaces 50‑100
Low Activity 1
Medium Activity 2
High Activity 2
Playground 5
Basketball Court: Recreational 10
Baseball: Recreational 10‑15
Tennis Court: Club 20
Basketball Court: High School 30

Mounting Height Guide

Bulb Type Mounting Height
70 Watts
High Pressure Sodium (HPS) 10‑15'
Metal Halide (MH) -
Mercury Vapor -
Tungsten/Halogen -
100 Watts
High Pressure Sodium (HPS) 15‑20'
Metal Halide (MH) -
Mercury Vapor -
Tungsten/Halogen -
150 Watts
High Pressure Sodium (HPS) 20‑55'
Metal Halide (MH) -
Mercury Vapor -
Tungsten/Halogen -
175 Watts
High Pressure Sodium (HPS) -
Metal Halide (MH) -
Mercury Vapor 18‑23'
Tungsten/Halogen -
200 Watts
High Pressure Sodium (HPS) 20‑25'
Metal Halide (MH) -
Mercury Vapor 18‑23'
Tungsten/Halogen -
250 Watts
High Pressure Sodium (HPS) 22‑27'
Metal Halide (MH) 20‑25'
Mercury Vapor 20‑25'
Tungsten/Halogen -
400 Watts
High Pressure Sodium (HPS) 30‑35'
Metal Halide (MH) 25‑30'
Mercury Vapor 20‑25'
Tungsten/Halogen -
500 Watts
High Pressure Sodium (HPS) -
Metal Halide (MH) -
Mercury Vapor -
Tungsten/Halogen 15‑20'
1000 Watts
High Pressure Sodium (HPS) 40‑50'
Metal Halide (MH) 40‑45'
Mercury Vapor 35‑40'
Tungsten/Halogen 25‑30'
1500 Watts
High Pressure Sodium (HPS) -
Metal Halide (MH) -
Mercury Vapor -
Tungsten/Halogen 25‑30'

Light Depreciation Chart

Clean Environment 0.96
Medium Environment 1.01
Dirty Environment 1.06

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Warning: When using this information to perform electrical work, call a licensed electrician and consult the NEC® for safety. All licensed electricians have passed examinations covering the National Electric Code®, know state and local building codes, and may carry insurance to cover damages.