Convert Lumens/Square Foot to Flame Phots
Lumen/Square Foot (lm/ft²) to Flame Phot (ph (flame)) illuminance conversion — enter any value below to get an instant result, or use the table for common values.
Results from this calculator are estimates provided for general informational purposes only, based on formulas, rates, and standards commonly accepted as of 2026. Figures may differ slightly from other calculators or professional sources due to rounding methods, differing assumptions, or regional regulations, and rules may change over time. Always consult a qualified professional — such as a financial advisor, healthcare provider, or other relevant specialist — before making decisions based on these results.
Result
1 lm/ft² = 0.25 ph (flame)
1 Lumen/Square Foot = 0.25 Flame Phots
1 Flame Phot = 4 Lumens/Square Foot
1 lm/ft² in every supported unit
Conversion chart: Lumen/Square Foot to Flame Phots
Conversion table
| Lumen/Square Foot (lm/ft²) | Flame Phot (ph (flame)) |
|---|---|
| 0.01 lm/ft² | 0.0025 ph (flame) |
| 0.1 lm/ft² | 0.025 ph (flame) |
| 1 lm/ft² | 0.25 ph (flame) |
| 2 lm/ft² | 0.5 ph (flame) |
| 3 lm/ft² | 0.75 ph (flame) |
| 5 lm/ft² | 1.25 ph (flame) |
| 10 lm/ft² | 2.5 ph (flame) |
| 20 lm/ft² | 5 ph (flame) |
| 50 lm/ft² | 12.5 ph (flame) |
| 100 lm/ft² | 25 ph (flame) |
| 1000 lm/ft² | 250 ph (flame) |
Lumen/Square Foot (lm/ft²)
Definition: Luminous flux per unit area expressed in square feet, numerically identical to the foot-candle since both describe one lumen spread over one square foot of surface.
History: Used in US customary engineering and lighting specifications where an explicit flux-per-area ratio is preferred over the named foot-candle unit, particularly in technical datasheets.
Current use: Common on American luminaire and sensor datasheets as an alternative way of writing foot-candle values.
Flame Phot (ph (flame))
Definition: A rare CGS-derived illuminance unit occasionally encountered in older flame-photometry and specialized lighting literature, historically defined relative to the phot at roughly 43.06 lux.
History: Emerged from specialized 20th-century photometric work that needed an intermediate scale between the lux and the far larger phot, though it never achieved wide adoption outside niche technical fields.
Current use: Almost never used today; it survives mainly as a legacy conversion entry in historical photometric references and unit-conversion tables.
Supported Units
| Unit | Symbol | In Lux |
|---|---|---|
| Lux | lx | 1 lx |
| Meter-candle | m·c | 1 lx |
| Centimeter-candle | cm·c | 10000 lx |
| Foot-candle | fc | 10.76391 lx |
| Flame Phot | ph (flame) | 43.055642 lx |
| Phot | ph | 10000 lx |
| Nox | — | 0.001 lx |
| Candela Steradian/Square Meter | cd·sr/m² | 1 lx |
| Lumen/Square Meter | lm/m² | 1 lx |
| Lumen/Square Centimeter | lm/cm² | 10000 lx |
| Lumen/Square Foot | lm/ft² | 10.76391 lx |
| Watt/Square Centimeter (at 555 nm) | W/cm² | 6830000 lx |
About These Parameters
- Value
- The illuminance value you want to convert, expressed in the "From" unit. Accepts decimals, and can represent anything from faint starlight to bright studio lighting.
- From Unit
- The unit your input value is currently measured in — a light meter's lux reading, a lighting code's foot-candle requirement, or a scientific instrument's phot or nox figure.
- To Unit
- The unit you want the result converted into. Use the swap button to flip From and To instantly.
How Illumination Conversion Works
The Formula
Every unit here is defined by a fixed multiplier relative to lux. To convert a value from one unit to another:
result = value × (factor of "From" unit ÷ factor of "To" unit)
For Lumen/Square Foot → Flame Phot: multiply by 0.25. For example, 1 lm/ft² × 0.25 = 0.25 ph (flame).
Lux vs. Foot-candles
Lux and foot-candles are the metric and US customary measures of the same underlying idea — luminous flux landing on a surface — and the divide between them tracks the broader metric/imperial split. One foot-candle equals about 10.76 lux, because a square foot is much smaller than a square meter. Most of the world specifies lighting requirements in lux, but US architectural and lighting codes, published by bodies like the Illuminating Engineering Society (IES), still specify recommended illuminance in foot-candles, so American lighting designers routinely need to convert between the two.
Typical Illuminance Levels
For context, here's roughly where common lighting conditions fall on the lux scale:
- Direct summer sunlight: ~100,000+ lux
- Full daylight (not direct sun): ~10,000-25,000 lux
- Overcast daylight: ~1,000 lux
- Typical office lighting: ~300-500 lux
- Living room lighting: ~50-150 lux
- Twilight: ~10 lux
- Full moonlight: ~1 lux
- Starlight (clear night sky): ~0.001 lux
Example
An illuminance of 1 lm/ft² equals 0.25 ph (flame). For scale, a well-lit office sits around 300-500 lux (roughly 28-46 foot-candles), while overcast daylight reaches about 1,000 lux and full moonlight is only about 1 lux.
Frequently Asked Questions
How many Flame Phots are in 1 Lumen/Square Foot?
1 Lumen/Square Foot (lm/ft²) equals exactly 0.25 Flame Phots (ph (flame)).
What's the difference between illuminance and luminance?
Illuminance (measured in lux or foot-candles) is the amount of light falling on a surface. Luminance is how bright that surface actually appears to an observer, which depends on both the illuminance and how much light the surface reflects. A white wall and a black wall under the same illuminance have very different luminance.
How many lux is one foot-candle?
One foot-candle equals approximately 10.7639 lux. This is why US lighting specifications in foot-candles produce noticeably larger numbers than the equivalent metric lux specification for the same physical brightness.
What is a phot and why is it so large?
A phot is the CGS-system unit of illuminance, defined as one lumen per square centimeter. Because a square centimeter is 10,000 times smaller than a square meter, one phot equals 10,000 lux — an enormous illuminance rarely encountered at full scale, which is why phot values are often expressed in millphots or microphots instead.
When would I use the nox unit?
Nox (1 nox = 0.001 lux) is used for very low illuminance levels, such as those encountered in night-vision equipment specifications or low-light astronomical and research work, where ordinary lux figures would require awkward, hard-to-read decimals.
How accurate are these conversions?
Every conversion factor used here is the standard, internationally recognized relationship between the underlying illuminance units — results are limited only by floating-point display precision, not by rounded conversion constants.