LightLight

IlluminationIllumination

Ray Model of Light-travels in a straight Ray Model of Light-travels in a straight path, can only be changed by placing an path, can only be changed by placing an obstructionobstruction

Luminous =SunLuminous =Sun

Illuminated = MoonIlluminated = Moon

OpaqueOpaque

TransparentTransparent

TranslucentTranslucent

QuanityQuanity

Luminous Flux (P)-Unit- LUMEN (lm) Luminous Flux (P)-Unit- LUMEN (lm) – Rate at which light is emitted from a luminous Rate at which light is emitted from a luminous

sourcesource

Illuminance (E)- Unit-LUX (lx)Illuminance (E)- Unit-LUX (lx)– illumination of a surface or the rate at which illumination of a surface or the rate at which

light strikes the surfacelight strikes the surface

Luminance Intensity- Unit: Candela (cd)Luminance Intensity- Unit: Candela (cd)– Luminous flux that falls on 1 mLuminous flux that falls on 1 m22

E=P/4 pi rE=P/4 pi r22

Practice ProblemPractice Problem

What is the illuminance on your desktop if it What is the illuminance on your desktop if it is lighted by 1750 lm lamp that is 2.5 m is lighted by 1750 lm lamp that is 2.5 m above your desk?above your desk?

22.3 lx22.3 lxA public school law requires a minimum A public school law requires a minimum illuminance of 160 lx at the surface of each illuminance of 160 lx at the surface of each student’s desk. An architect’s specifications student’s desk. An architect’s specifications call for classroom lights to be located 2.0 m call for classroom lights to be located 2.0 m above the desks. What is the miniumum above the desks. What is the miniumum luminous flux that the lights must provide?luminous flux that the lights must provide?

8042 lm8042 lm

Remember Waves!Remember Waves!

DiffractionDiffraction

RelfectionRelfection

RefractionRefraction

PolarizationPolarization

Production of light in a single plane of Production of light in a single plane of oscillationoscillation

Only parallel can pass throughOnly parallel can pass through