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 outdoor 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 the decimal. Number of Fixtures = 5
Note: This is not a precise lighting guide.
Foot Candle Table
| 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 |
| Manufactering 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 |
| Basketball Court: Recreational | 10 |
| Baseball: Recreational | 10‑15 |
| Tennis Court: Club | 20 |
| Basketball Court: High School | 30 |
Mounting Height Guide
| Watts | High Pressure Sodium (HPS) | Metal Halide (MH) | Mercury Vapor | Tungsten / Halogen |
|---|---|---|---|---|
| 70 | 10‑15′ | – | – | – |
| 100 | 15‑20′ | – | – | – |
| 150 | 20‑25′ | – | – | – |
| 175 | – | – | 18‑23′ | – |
| 200 | 20‑25′ | – | – | – |
| 250 | 22‑27′ | 20‑25′ | 20‑25′ | – |
| 400 | 30‑35′ | 25‑30′ | 20‑25′ | – |
| 500 | – | – | – | 15‑20′ |
| 1000 | 40‑50′ | 40‑45′ | 35‑40′ | 20‑25′ |
| 1500 | – | – | – | 25‑30′ |
Light Depreciation Chart
| Clean Environment | Medium Environment | Dirty Enviroment |
|---|---|---|
| 0.96 | 1.01 | 1.06 |
