2 Photometry.pdf - EE512 Electrical Illumination and Design Photometry Photometry Photometry The science of measurement of visible light in terms of its

# 2 Photometry.pdf - EE512 Electrical Illumination and Design...

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Electrical Illumination EE512 and Design
Photometry
Photometry Photometry The science of measurement of visible light in terms of its perceived brightness to human vision It is the measurement of light's brightness, or luminous intensity. Photometry frequently focuses on the perceived brightness to the human eye. As such, it takes into account the eye's sensitivity to varying degrees of light and focuses primarily on the visible light spectrum.
Definitions 1. Candela (cd) The SI unit of luminous intensity, or power emitted by a light source in a particular dimension. A common candle emits light of approximately one (1) candela. A source of one candela emits one lumen per steradian.
Definitions 2. Luminous Flux (F or Φ) or Luminous Power All the radiated power emitted by a light source and is perceived by the eye is called luminous flux It is the light energy radiated out per second from the body in the form of luminous light waves Luminous Flux “Total Power” “light power” “Light output”
Definitions 2. Luminous Flux (F or Φ) or Luminous Power Since it is a rate of flow of energy, we can consider it to be a sort of power unit. The unit of luminous flux is lumen (lm). Which is defined as the flux contained per unit solid angle of a source of one candela. 1 lumen is approximately 0.0016 watts.
Definitions 3. Luminous Intensity ( I ) or Candle Power The luminous intensity or candle power of a point source in any particular direction is given by the luminous flux radiated out per unit solid angle in that direction. It is the solid angular flux density of a source in a specified direction. I = Where: dΦ is the luminous flux radiated out by a source within a solid angle of dω steradian in any direction.
Definitions 3. Luminous Intensity ( I ) or Candle Power With the flux measure in lumens and the solid angle in steradians, the unit of Luminous intensity is lumen/steradian (lm/sr) or candela (cd) Luminous Intensity “Total Power / Solid angle” “candle power”

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• Summer '19
• Photometry, Physical quantities, Luminous flux, Luminosity function, Luminous Power