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Illumination & Illuminance Converter

Convert light incident upon a surface across Lux (lx), Foot-candles (fc), and Phots (ph) with real-time bidirectional calculations and inverse-square lighting laws.

Explore Illumination & Illuminance Guide & Formulas↓View Illumination & Illuminance Converter Chart→

Formula

Simultaneous Category Equivalents

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Popular Illumination & Illuminance Conversion Shortcuts

Instant pair conversions with verified scientific and mathematical formulas

Quick Pairs

Foot-candles to Phots→

1,000 fc = 1.0764 Phots

Phots to Foot-candles→

1 Phot = 929.03 fc

500 Lux to fc (Office Standard)→

500 Lux ≈ 46.45 fc

100 fc to Lux→

100 fc = 1,076.39 Lux

Illumination & Illuminance Reference Equivalents (1 Lux)

Standard ratios measured against the base Lux (lx)

Reference Table

Unit Name	Symbol	Equivalent in 1 lx	Quick Pair Page
Lux	lx	1 lx = 1 lx	Base Unit
Foot-candle	fc	1 lx = 0.092903 fc	lx to fc →
Phot	ph	1 lx = 0.0001 ph	lx to ph →

Architectural & Natural Illuminance Standards Reference Chart

Lookup table of standard lighting levels from moonlit night skies to surgical operating suites and direct midday sunlight

Lookup Matrix

Visual Environment / Task	Lux (lx) (SI)	Foot-candles (fc)	Phots (ph)	IESNA / OSHA Standard Guideline
Clear Night Sky under Full Moon	0.25 lx	0.023 fc	0.000025 ph	Night Orientation / Security
Public Street Lighting at Night	10.0 lx	0.93 fc	0.0010 ph	Municipal Roadway Safety
Residential Living Room / Dining	150.0 lx	13.94 fc	0.0150 ph	Casual Domestic Relaxation
Corridor & Warehouse Walkway	100.0 lx	9.29 fc	0.0100 ph	OSHA Warehouse Passage Minimum
Standard Commercial Office Desk	500.0 lx	46.45 fc	0.0500 ph	IESNA Reading & Computer Work
Mechanical Drafting & Precision Assembly	1,000.0 lx	92.90 fc	0.1000 ph	Fine Inspection Workstations
Hospital Surgical Operating Suite Table	10,000.0 lx	929.03 fc	1.0000 ph	Surgical Cavity Precision Focus
Television Broadcast Production Studio	2,000.0 lx	185.81 fc	0.2000 ph	Camera Sensor Aperture Quality
Overcast Cloud Daylight Outdoors	1,000.0 lx	92.90 fc	0.1000 ph	Natural Daylight Diffuse
Direct Midday Summer Sunlight	100,000.0 lx	9,290.30 fc	10.0000 ph	Unshaded Sun Zenith Maximum

Photometry & Architectural Optics

Illuminance: Photometric Quantities, Inverse-Square Law & Lighting Codes

Authoritative guide to illuminance, lumens incident per area, CIE photopic eye response curves, and unit conversions across architectural and stage lighting.

Photometric Incident Flux & Lux Definition

Illuminance E quantifies the density of visible light luminous flux incident upon an illuminated plane:

E = dΦ / dA = (I · cos(θ)) / d²

Lambert's Cosine Law & Inverse-Square Equation (Φ = Luminous Flux in Lumens, I = Luminous Intensity in Candelas, θ = Incidence Angle)

Unlike radiometric irradiance (measured in pure physical Watts per square meter), photometric illuminance scales optical radiation according to the standardized CIE Photopic Luminosity Function V(λ), which peaks at 555 nanometers (human green-yellow spectral sensitivity).

SI Lux vs. Imperial Foot-Candles Standards

Building regulations around the world specify lighting code compliance:

SI Metric Standard: Lux (lx)

1 Lux = 1 Lumen/m². Standard in European (EN 12464) and international ISO building performance standards for interior lighting ergonomics.

North American Standard: Foot-Candle (fc)

1 Foot-candle = 1 Lumen/ft² ≈ 10.764 Lux. Retained across US OSHA workplace safety regulations and North American architectural specifications.

Lighting Energy Efficiency & Uniformity Ratios

Modern solid-state LED luminaires produce 100 to 180 lumens per electrical Watt. In professional architectural planning, engineers assess not only peak Lux, but also the Uniformity Ratio (U₀ = E_min / E_avg), guaranteeing that office workstations do not suffer from sharp light-to-shadow contrasts that provoke visual fatigue.

About Illumination & Illuminance Units & Formulas

1 Foot-candle ≈ 10.76391 Lux | 1 Phot = 10,000 Lux.

Luxlx

SI unit of illuminance (1 lm/m²)

Foot-candlefc

Imperial illuminance (1 lm/ft²)

Photph

CGS unit (1 lm/cm²)

FREQUENTLY ASKED QUESTIONS

Illumination & Illuminance Converter FAQs

Frequently asked questions regarding illumination & illuminance conversion metrics, formulas, and real-world calculation standards

How do you convert Lux to Foot-candles (lx to fc)?

To convert Lux (lx) to Foot-candles (fc), divide by 10.76391 or multiply by 0.092903: fc = Lux × 0.092903.

Physical Relationship:

1 Lux = 1 Lumen per square meter (lm/m²).
1 Foot-candle = 1 Lumen per square foot (lm/ft²).
Because 1 square meter contains approximately 10.7639 square feet (1 m² = 10.7639 ft²), 1 Foot-candle ≈ 10.764 Lux.
Reverse Conversion: Multiply Foot-candles by 10.7639 to get Lux (e.g., 50 fc × 10.764 = 538.2 Lux).

What is illuminance in photometry?

Illuminance (E) is the total luminous flux incident on a surface per unit area (E = Φ ÷ A = Lumens ÷ Area).

SI Derived Unit: Lux (lx), equivalent to 1 Lumen per square meter (lm/m²).
Imperial Unit: Foot-candle (fc), equivalent to 1 Lumen per square foot (lm/ft²).
Illuminance vs Luminance: Illuminance measures light falling onto a surface (independent of surface reflectance), while luminance measures light reflected or emitted from a surface into an observer's eye.

What is the Inverse-Square Law of lighting?

For a point light source emitting uniformly, illuminance is inversely proportional to the square of the distance (d) from the source:

E = I / d²

If you double the distance from a lamp (e.g., moving from 1 meter to 2 meters away), the illuminance drops by a factor of 4 (2²), receiving only 25% of the original light.

How many Lux are recommended for a home office or computer desk?

Under Illuminating Engineering Society (IESNA) guidelines, a modern computer workstation requires 300 to 500 Lux (approximately 30 to 50 Foot-candles) of ambient task lighting.

Excessive illuminance (> 1,000 Lux) creates harsh display monitor glare and visual fatigue, while insufficient lighting (< 200 Lux) induces eye strain during paper reading.