BASIC PARAMETERS USED IN LIGHTING

THE LIGHTING HANDBOOK – CHAPTER 1

Luminious flux – Luminious intensity – Illuminance – Luminance

Ω = solid angle into which luminous flux is emitted

A = area hit by luminous flux

AL · cosϵ = visible areas of light source

p = reflectance of area

π = 3.14

* = for diffuse surface areas

Luminous flux

The luminous flux describes the quantity of light emitted by a light source.

The luminous efficency is the ratio of the luminous flux to the electrical power consumed (lm/W). It is a measure of a light source’s economic efficency.

Abbreviation: Φ Phi Unit: lm Lumen

Luminous intensity

The luminous intensity describes the quantity of light that is radiated in a particular direction. This is a useful measurement for directive lighting elements sush as reflectors. It is represented by the luminous intensity distribution curve (LDC)

Abbreviation: I Unit: cd Candela

Illuminance

Illuminance describes the quantity of luminous flux falling on a surface. Relevant standards specify the required illuminance (e.g. EN 12464 “Lighting of indoor workplaces”)

Illuminance: E(lx) = [𝑙𝑢𝑚𝑖𝑛𝑜𝑢𝑠 𝑓𝑙𝑢𝑥 (𝑙𝑚)] / 𝑎𝑟𝑒𝑎 (𝑚2)

Abbreviation: E Unit: lx Lux

Luminance

Luminance is the only basic lighting parameter that is perceived by the eye.

It describes on the one hand a light source’s inpression of brightness, and on the other, a surface and therefore depends to a large extent on the degree of reflection (colour and surface).

Abbreviation: L Unit: cd/m2