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Luminous Unit Converter

Convert between luminous intensity, luminance, and illuminance units such as candela, nit, lux, footcandle, lambert, and more.

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Overview

Light measurement covers three key quantities:

  • Luminous Intensity (candela): brightness emitted in a direction.
  • Luminance (nit, cd/m²): brightness per area on a surface.
  • Illuminance (lux, footcandle): luminous flux received per area.

Formula & Methodology

All conversions pivot through SI base (candela for intensity, cd/m² for luminance, lm/m² for illuminance):
\( X_{\!SI} = X_{\text{input}} \times f_{\text{from}} \)
\( X_{\text{output}} = \frac{X_{\!SI}}{f_{\text{to}}} \)

Examples

  • 50 cd → candela-per-ft²: 50 cd ÷ 0.092903 = ~538.2 cd/ft²
  • 300 lux → footcandle: 300 lx ÷ 10.7639 ≈ 27.87 fc
  • 1000 cd/m² (nit) → lambert: 1000 ÷ 3183.1 ≈ 0.314 L

Use Cases

  • Display brightness: monitors ~200–400 cd/m².
  • Photography: recommended ~100–500 lux for indoor shooting.
  • Art galleries: 50–200 lux to protect artwork.

Frequently Asked Questions

What is candela?

The SI base unit for luminous intensity: light emitted per solid angle.

What’s a nit?

Nit = cd/m², used for screen brightness specs.

Why footcandle vs lux?

FC (imperial) vs lx (metric): 1 fc = 10.7639 lx.

What is lambert?

Unit of luminance: 1 L = 10⁴/π cd/m² ≈ 3183.1 cd/m².

How does this affect photography?

Illuminance dictates exposure settings; use lux→fc conversion for older light meters.