Understanding Luminous Flux

Luminous flux measures the total quantity of visible light emitted by a source per unit time, weighted according to the human eye's sensitivity to different wavelengths.

Introduction

Luminous flux is a photometric quantity that measures the perceived power of light by the human eye. It accounts for the eye's varying sensitivity to different wavelengths of light, making it essential for lighting design and energy efficiency.

History

Photometry developed in the 18th century with Pierre Bouguer's work on light measurement. The lumen was defined in 1979 as part of the SI system, based on the candela and the concept of solid angles. Modern LED technology has revolutionized how we think about luminous efficiency.

Key Units

Lumen (lm)

The SI unit of luminous flux, equal to the light emitted by one candela in a solid angle of one steradian.

Candlepower

An older unit roughly equivalent to the light from one candle, now largely replaced by the candela and lumen.

Applications

  • LED and lighting fixture specifications
  • Architectural and interior lighting design
  • Energy efficiency calculations and building codes
  • Photography and cinematography lighting setups
  • Automotive headlight and taillight standards
  • Display technology and screen brightness measurement

Luminous Flux Calculation

Φ = I × Ω

Luminous flux (Φ) equals luminous intensity (I) multiplied by the solid angle (Ω) in steradians.