Foot-candle to Phot Conversion Table
| Foot-candle (fc) | Phot (ph) | Reference Benchmark | Formula Step |
|---|---|---|---|
| 0.000093 fc | 1e-7 ph | Overcast night sky with starlight only | 0.000093 × 0.001076 = 0.0000001 ph |
| 0.0232 fc | 0.000025 ph | Full moon on a clear night at sea level | 0.0232 × 0.001076 = 0.000025 ph |
| 0.0929 fc | 0.0001 ph | Emergency pathway and exit corridor egress lighting | 0.0929 × 0.001076 = 0.0001 ph |
| 0.929 fc | 0.001 ph | Residential hallway and twilight ambient outdoor light | 0.929 × 0.001076 = 0.001 ph |
| 4.645 fc | 0.005 ph | Residential living room or cinema auditorium ambient lighting | 4.645 × 0.001076 = 0.005 ph |
| 9.29 fc | 0.01 ph | Warehouse bulk storage aisles and commercial stairwells | 9.29 × 0.001076 = 0.01 ph |
| 18.581 fc | 0.02 ph | General dining room and school classroom background light | 18.581 × 0.001076 = 0.02 ph |
| 27.871 fc | 0.03 ph | Library reading room and hotel conference workspace | 27.871 × 0.001076 = 0.03 ph |
| 46.452 fc | 0.05 ph | Standard commercial open-plan computer office desktop | 46.452 × 0.001076 = 0.05 ph |
| 69.677 fc | 0.075 ph | Technical CAD drafting and mechanical inspection bench | 69.677 × 0.001076 = 0.075 ph |
| 92.903 fc | 0.1 ph | Precision electronic manufacturing and watchmaking bench | 92.903 × 0.001076 = 0.1 ph |
| 185.806 fc | 0.2 ph | Hospital operating surgical theater task illumination | 185.806 × 0.001076 = 0.2 ph |
| 464.515 fc | 0.5 ph | Television broadcasting studio lighting stage | 464.515 × 0.001076 = 0.5 ph |
| 929.03 fc | 1 ph | Overcast overcast midday outdoor daylight | 929.03 × 0.001076 = 1 ph |
| 2322.576 fc | 2.5 ph | Full indirect daylight under clear blue sky | 2,322.576 × 0.001076 = 2.5 ph |
| 9290.304 fc | 10 ph | Direct overhead tropical noon sunlight | 9,290.304 × 0.001076 = 10 ph |
Foot-candle to Phot Formula & Unit Definitions
The exact ratio derives from imperial-to-metric geometric surface definitions: 1 foot equals 30.48 centimeters, which means 1 square foot equals (30.48 cm)² = 929.0304 square centimeters. Since 1 foot-candle = 1 lm / 929.0304 cm², dividing 1 by 929.0304 yields exactly 0.00107639104 phot per foot-candle. Consequently, multiplying any foot-candle value by 0.00107639104 converts it directly to phot.
Quick Estimation: To estimate foot-candles to phot mentally, divide by 930 (or multiply by 1.08 and divide by 1,000). For example, bright noon sunlight at 9,300 foot-candles corresponds to approximately 10 phot.
Foot-candle (fc)
Source Unit- Primary US customary unit of illuminance (lumen per square foot, lm/ft²).
- Mandated standard across North American building codes, OSHA guidelines, and architectural blueprints.
- Covers human-scale lighting where typical office desktops range from 30 to 50 fc.
Phot (ph)
Target Unit- Centimetre-gram-second (CGS) metric illuminance unit (lumen per square centimeter, lm/cm²).
- Historically standard in microscopy, photography, and early optical physics.
- Represents 929.03 times greater luminous density per unit area than a foot-candle.
Frequently Asked Questions
Q.How do you convert foot-candles to phot accurately?
Multiply the illuminance in foot-candles by approximately 0.00107639 (or divide by 929.03). For instance, 929.03 foot-candles divided by 929.03 equals exactly 1 phot.
Q.What is the exact mathematical ratio between foot-candles and phot?
One phot equals exactly 929.0304 foot-candles because 1 square foot contains exactly 929.0304 square centimeters. Conversely, 1 foot-candle equals 0.00107639104 phot.
Q.What is the physical difference between Foot-candle and Phot?
Foot-candle measures luminous flux per square foot (lm/ft²) used in American building codes, while Phot is a CGS metric unit measuring luminous flux per square centimeter (lm/cm²).
Q.Why is 1 phot equal to roughly 929 foot-candles?
Because one square foot (12 in × 12 in) equals exactly 929.0304 square centimeters. Therefore, concentrating 1 lumen into 1 cm² represents 929.0304 times higher density than 1 lumen spread across 1 ft².