What is the difference between lux and foot-candles?

Both measure illuminance (light falling on a surface). One foot-candle equals approximately 10.764 lux. Foot-candles are used in the US; lux is the SI standard used globally.

How do lumens differ from lux?

Lumens measure total luminous flux emitted by a source (output). Lux measures how much of that light lands on a surface per square meter. A 1-lumen source uniformly lighting 1 m² produces 1 lux.

What is a nit in photometry?

A nit is a unit of luminance equal to 1 candela per square meter (cd/m²). It is commonly used to describe the brightness of displays, TVs, and monitors.

What are stilb and lambert?

Stilb (sb) and lambert (L) are older CGS units of luminance. One stilb equals 10,000 cd/m² (nits). One lambert equals 1/π cd/cm² ≈ 3,183.1 cd/m².

Can I convert lumens to lux directly?

Not without knowing the area. Lux = lumens ÷ area (m²). This tool converts within unit families — flux-to-flux or illuminance-to-illuminance — where a direct factor exists.

Photometry Unit Converter

Name: Photometry Unit Converter
Availability: InStock
Author: Nham Vu

Convert lumens, candela, lux, foot-candles, nits, stilb, and lambert with instant results and a full unit reference table.

Photometry Converter

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Enter a value on the left to see conversions.

Photometric Unit Reference

Common units, their symbols, what they measure, and typical use cases.

Unit	Symbol	Quantity	Definition	Typical Use
Lumen	lm	Luminous Flux	SI base unit of luminous flux	Lamp output, LED packages
Candela	cd	Luminous Intensity	SI base unit; flux per steradian	Directional lights, headlights
Lux	lx	Illuminance	1 lm per m²	Workplace lighting, photography
Foot-candle	fc	Illuminance	1 lm per ft² ≈ 10.764 lx	US lighting standards, film/TV
Phot	ph	Illuminance	CGS unit; 1 lm per cm² = 10,000 lx	Older scientific literature
Nit	nt	Luminance	1 cd per m²	Display brightness, HDR specs
Stilb	sb	Luminance	CGS unit; 1 cd per cm² = 10,000 cd/m²	Legacy optics, CRT specs
Lambert	L	Luminance	(1/π) cd/cm² ≈ 3183.1 cd/m²	Older photometric reports
Foot-lambert	fL	Luminance	(1/π) cd/ft² ≈ 3.4263 cd/m²	Cinema projection, US standards
Apostilb	asb	Luminance	(1/π) cd/m² ≈ 0.3183 cd/m²	European older standards

Summary

Convert lumens, candela, lux, foot-candles, nits, stilb, and lambert with instant results and a full unit reference table.

How it works

Select the photometric quantity group: flux, illuminance, or luminance.
Enter a numeric value in the input field.
Choose the source unit from the dropdown.
All equivalent values in other units appear instantly.
Use the reference table below to understand what each unit measures.

Use cases

Convert manufacturer lux specs to foot-candles for US lighting standards.
Check if display brightness in nits meets HDR thresholds.
Translate luminous flux specs between lumens for different lamp types.
Convert stilb or lambert values from older scientific papers.
Verify illuminance levels against OSHA or IESNA recommendations.
Cross-reference camera exposure data that uses foot-candles.

Frequently Asked Questions

Last updated: 2026-07-23 · Reviewed by Nham Vu