Definitions related to illumination
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This document defines and explains key terms related to illumination: Illuminance is the amount of light falling on a surface, measured in lux which is equal to one lumen per square meter. Luminance is the luminous intensity emitted per unit area of a light source, measured in candela per square meter. Luminous flux, measured in lumens, is the total perceived power of light emitted by a source in all directions. Luminous intensity is the luminous flux emitted in a given direction within a unit of solid angle, measured in candelas.
Definitions related to illumination
- 2. IILUMINATION • This definition determines the amount of light that covers a surface. • If Ø is the luminous flux and S is the area of the given surface then the illuminance E is determined by E=Ø/S. • The unit of illumination in SI system is lux. • One lux (lx) is the illuminance of 1 m² surface area uniformly lighted by 1 lm of luminous flux.
- 3. • Lux is luminous flux per unit area. • It is equal to one lumen per square meter. 1 lx = 1 lm/m² • A lux meter is used for measuring illuminances in work places.
- 5. LUMINANCE • Luminance L is the luminous intensity emitted by the surface area of 1 cm² (or 1 m²) of the light source. • It is a photometric measure of the luminous intensity per unit area of the light travelling in a given direction.
- 6. •Mathematically it is L=I/S where I is the luminous intensity and S is the area of the source surface perpendicular to the given direction. •SI Unit : Candela per square meter (cd/m²)
- 7. •Used to characterize emission or reflection from flat, diffuse surfaces. •Indicates how much luminous power will be detected by an eye looking at the surface from a particular angle of view.
- 8. LUMINOUS FLUX • Also known as luminous power is the measure of the perceived power of light • It is the quantity of the energy of the light emitted per second in all directions. • SI Unit : lumen (lm)
- 9. • One Lumen : is defined as the luminous flux of light produced by a light source that emits one candela of luminous density over a solid angle of one steradian • It is the luminous flux of the uniform point light source that has luminous intensity of 1 candela and is contained in one unit of spatial angle (or 1 steradian). • Steradian is the spatial angle that limits the surface area of the sphere equal to the square of the radius.
- 11. LUMINOUS INTENSITY • Luminous intensity is the ability to emit light into a given direction, or it is the luminous flux that is radiated by the light source in a given direction within the unit of the spatial angle. • If the point light source emits Ø lumens into a small spatial angel ß, the luminous intensity is I=Ø/ß. • The unit of luminous intensity is candela.