photometry & radiometry

Bonnie Cooper

Luminous Power
- Total percieved light power emitted from a light source
- Units: Lumens
Radiometric Power:
- Total emitted radiant energy from a radiant body
- Units: Watts, J/sec

Luminous power? ….radiant power?

No, Luminous & Radiant power quantifies the light emitted from a source

Luminous power? ….radiant power?

…maybe?

introducing the goniophotometer:

Luminous Intensity
- light power emitted per solid angle by a point source
- Units: candela (cd) = lumen/steridian
- steridian (sr) = an SI derived unit of solid angle
Radiant Intensity
- radiant power emitted per solid angle by a point source
- Units: Watts/steridian

a specific example: spectroradiophotometer

Luminance
- luminous intensity per unit area by an extended source
- Units: candela/$ m^2 $, Foot-lamberts
Radiance
- radiant intensity per unit area by an extended source
- Units: Watts/steridian/$ m^2 $

…presenting a luminance meter:

Illuminance
- luminous intensity incident to a unit of surface area
- Units: lux, lumens/$ m^2 $, Foot-candles
Irradiance
- radiant intensity incident to a unit of surface area
- Units: Watts/$ m^2 $

Inverse Square Law \[ \mbox{Intensity } = \frac{1}{\mbox{distance}^2} \]

Measurement	Units	What does it measure?	What do you measure it with?
Luminous / Radiant Power	Lumens / Watts/sec	Total percieved light / radiant energy emitted from a light source	Goniophotometer
Luminous / Radiant Intensity	candela, lumen/sr / Watts/sr	Luminous power / radiant power emitted per solid angle by a point source	Spectroradiometer
Luminance / Radiance	candela/$ m^2 $, foot-lamberts / Watts/sr/$ m^2 $	Luminous / radiant intensity per unit area of an extended source (Can be a light source or any surface)	Luminance Meter
Illuminance / Irradiance	lux, lumens/$ m^2 $, foot-candles / Watts/$ m^2 $$	Luminous / Radiant intensity incident to a unit of surface area	Illuminance Meter

Let's explore this in more depth in this jupyter notebook