Illuminance Converters

Convert between lx, klx, fc, and ph using exact lux-based illuminance relationships. This hub covers lighting-design, exposure, and architectural reference values with dedicated mirror pages.

Scope & Verification

This hub groups related converter families so you can move from the category level to exact routes with one clear basis per page.

  • Families are split so exact-factor, profile-based, density-based, and estimate-style pages do not collapse into one generic answer.
  • Leaf pages keep calculator, common values, FAQ, and reverse routes aligned to the same assumption.
  • Methodology and verification pages document how those assumptions are chosen and checked.
Methodology How We Verify Editorial Policy

Explanation

Illuminance is luminous flux per unit area incident on a surface. In SI, illuminance is measured in lux (lx), where 1 lx = 1 lm/m², and kilolux (klx) is an exact base-10 scaling of lux. Foot-candle (fc) is defined as lumens per square foot, giving 1 fc ≈ 10.7639 lx from the exact square-foot area relationship. Phot (ph) is a CGS unit defined as 1 lm/cm², which equals exactly 10,000 lx. All conversions in this hub are purely multiplicative with no offsets, and factors are derived by reducing each unit to lux using exact area relationships. For clarity, illuminance conversions are grouped into SI, imperial, and CGS systems.

Frequently Asked Questions

What is illuminance?

Illuminance quantifies how much luminous flux reaches a surface area.

What is the SI unit of illuminance?

The SI unit of illuminance is lux (lx), defined as lumens per square meter (lm/m²).

How many lux are in one foot-candle?

One foot-candle is approximately 10.7639 lux.

What is a phot?

A phot is a CGS illuminance unit defined as 1 lumen per square centimeter (1 lm/cm²).

Why is phot exactly 10,000 lux?

Because 1 cm² is exactly 1/10,000 m², so 1 lm/cm² equals exactly 10,000 lm/m² (10,000 lx).

Are illuminance conversions multiplicative?

Yes. Illuminance conversions are purely multiplicative with no additive offsets.

How do I switch direction?

Open the mirror page for the reverse conversion when you need the same lux-based relationship in the opposite direction.