# 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
Shipyards 5
General Building Construction 10
Corridors / Stairways / Restrooms 10‑20
Storage Rooms 10‑50
Storage Yards: Active 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
AIRPORTS
Terminal Apron / Parking 0.5
Hanger Aprons 1
BULLETIN BOARDS
Light Surfaces 20‑50
Dark Surfaces 50‑100
PARKING AREAS / VEHICULAR TRAFFIC
Low Activity 1
Medium Activity 2
High Activity 2
SPORTS
Playground 5
Baseball: Recreational 10‑15
Tennis Court: Club 20

## 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 1.01 1.06

### Available Lighting Products

#### The Lighting Showroom

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.