How do you convert lux and foot-candle (fc)? How many lux are in 1 fc?
1 fc (foot-candle) = 10.76391 lux (exact value), approximately 10.76 lux. Reverse: 1 lux = 0.0929 fc. The conversion comes from area units: 1 square foot = 0.0929 square meters, so 1 lm/ft² = 1/0.0929 lm/m² ≈ 10.764 lux. IESNA standards in North America commonly use fc; EU/international standards use lux.
What is a phot (ph)? How do you convert it to lux?
phot (symbol ph) is the illuminance unit in the CGS centimeter-gram-second system, defined as 1 lumen per square centimeter (1 lm/cm²). 1 ph = 10,000 lux = 10 klx (ten thousand lux). ph is a large unit often used to describe extremely high illuminance scenarios (e.g., direct sunlight, near-field of strong light sources). It has been replaced by lux in modern lighting engineering but still appears in some older literature and Eastern European national standards.
What is a nox (nx)? What's its relationship to lux?
nox (symbol nx) is a unit specifically for describing low-light/nighttime illuminance, 1 nx = 0.001 lux = 1 mlux (millilux), one-thousandth of a lux. Used for nighttime environments, astronomical observation, darkroom design, night-vision device parameters (e.g., moonlight ~0.1~1 lux = 100~1000 nx); this unit is not used for everyday lighting.
About how many lux are in everyday environments?
Common scenario illuminance references: starlight night 0.001~0.01 lux (1~10 nx), full moon night 0.1~1 lux, dusk road 1~10 lux, living room general lighting 50~100 lux, hallway/corridor 100~200 lux, office/classroom 300~500 lux, precision workbench/drafting room 500~1000 lux, overcast outdoors 1000~5000 lux, sunny shade 10,000~25,000 lux, direct sunlight 50,000~100,000 lux (50~100 klx).
What is the standard office illuminance in lux?
ANSI/IESNA standards: general office 30~50 fc (~320~540 lux), high-end office 500 lux, conference room 300 lux, corridor 100~200 lux, design/drafting room 500 lux. International standard: ISO 8995 recommends 500 lux for offices, 750~1500 lux for precision assembly.
What's the relationship between lux and EV values in photography metering?
Photographic EV (Exposure Value) to illuminance conversion is based on ISO 100: EV 0 ≈ 2.5 lux (moonlight level), EV 5 ≈ 80 lux (indoor), EV 10 ≈ 2560 lux (overcast), EV 12 ≈ 10,240 lux (bright overcast), EV 14 ≈ 40,960 lux (sunny shade), EV 15 ≈ 81,920 lux (direct sunlight). Approximate EV-to-lux relationship: lux ≈ 2.5 × 2ᴱⱽ (ISO 100). Studio light meters commonly give fc or lux readings.
How many lux do plants need to grow?
Light requirements vary widely by plant: shade plants (ferns, evergreens) 50~200 lux survive; common houseplants (pothos, monstera) 200~1000 lux; flowering plants (orchids, roses) need 1000~10,000 lux; vegetable seedlings/leafy greens 10,000~20,000 lux; succulents/cacti/tomatoes and other high-light crops 20,000~50,000 lux or more. Note that plants care more about PAR (Photosynthetically Active Radiation, μmol/m²/s) than lux, but lux works as a quick estimate.
What's the difference between lux and lumens (lm)? How do you convert?
Lumens (lm) are luminous flux (total light emitted by a source); lux are illuminance (light received per unit area on a surface). 1 lux = 1 lm/m²—1 lumen of light uniformly illuminating 1 square meter produces 1 lux illuminance. Conversion: Illuminance E(lux) = Luminous flux Φ(lm) × utilization factor × maintenance factor / area (m²). The same light source farther from the surface produces lower illuminance (inverse-square law).
How is illuminance different from luminance (cd/m²)?
Illuminance (lux) describes how much light is received on a surface (incident); luminance (cd/m², nit) describes how bright an emitting/reflecting surface appears to the eye (exitant). Relationship: Luminance L = ρ×E/π (ρ = reflectance, ideal diffuse surface). For example, a white wall (reflectance 0.8) at 500 lux illuminance has luminance ~127 cd/m². Typical screen brightness 200~500 cd/m², sun luminance ~1.6×10⁹ cd/m².
Why is fc-to-lux 10.764 instead of a whole number?
Because the foot-to-meter conversion is non-integer: 1 foot = 0.3048 meters, 1 square foot = 0.3048² = 0.09290304 square meters, so 1 lm/ft² = 1/0.09290304 = 10.76391... lm/m² ≈ 10.764 lux. This relates to length/area unit conversion—it's not a 1000x integer multiple like meters to millimeters. This is why you can't simply move the decimal point for illuminance conversion.
How many lux are needed for reading/writing in classrooms/studies?
Recommended reading/writing illuminance: ANSI/IESNA requires classroom desks 300 lux, library reading rooms 500 lux; bedside reading at night 150~300 lux (with desk lamp); close reading/student homework recommends desk lamp + ambient light together reaching 500 lux or more. For children's eye health, desk illuminance should not be below 500 lux, and uniformity (min/average) should not be below 0.7 to avoid eye strain from excessive contrast.
Will the illuminance values I enter be uploaded? Is my data private?
No uploads at all. All conversion logic runs locally in your browser using pure client-side JavaScript. The illuminance values you enter never make any network requests—servers cannot see your lighting design parameters or project data. Inputs are cleared immediately when you close the page; no cookies or localStorage are used. Suitable for lighting designers, photographers, architectural engineers, enterprise projects, and other data-sensitive scenarios.
