; Measurement of light

    ;luminous flux is the rate at which light energy is
    ; emitted from a source (over time), also known as "flow of light"
    ; flux = rate of flow of energy or fluid across a surface
    ; flux density = flux thru a unit of surface area
dimension LuminousFlux          Power
dimension RadiantPower          Power
dimension RadiantFlux           Power

    ;luminous intensity is luminous flux per solid angle
dimension LuminousIntensity     LuminousFlux per SolidAngle
dimension RadiantIntensity      LuminousIntensity
dimension CandlePower           LuminousIntensity

    ;illuminance is how much light energy strikes a given surface
dimension Illuminance           LuminousFlux per Area
dimension Illumination          Illuminance
dimension Irradiance            Illuminance
dimension RadiantFluxDensity    Illuminance

    ; luminance is amount of light reflected by a surface
    ; (the brightness of a surface)
dimension Luminance             LuminousIntensity per Area
dimension Brightness            Luminance
dimension Emittance             Luminance
dimension Radiance              Luminance

;1 candle produces 1 lumen of luminous flux thru an
;    area subtending a solidAngle of 1 steradian measured from the source.

unit sr             1.0         steradian               ; SolidAngle

unit Lumen          0.001496    watt                    ; LuminousFlux
unit lm             1.0         lumen                   ; LuminousFlux
unit Candela        1.0         lumens per steradian    ; LuminousIntensity
unit cd             1.0         candela                 ; LuminousIntensity
unit Candle         1.0         candela                 ; LuminousIntensity
unit FootCandle     1.0         lumen per foot^2        ; Illuminance
unit Phot           1.0         lumen per cm^2          ; Illuminance
unit lux            1.0         lumen per meter^2       ; Illuminance
unit FootLambert    3.426       candela per meter^2     ; Luminance
unit lambert        2.05339     candles per inch^2      ; Luminance

;Luminous efficiency:
;   For a given wavelength of electromagnetic
;   radiation, its relative ability to induce a sensation of 'light'.
;   It is a ratio, typically expressed as "lumens per watt".

;Reflectance:
;   The proportion of light reflected from a surface

; TO DO: figure out what a "lumberg" is

let minimum.visible.wavelength = 380 nanometers
let maximum.visible.wavelength = 780 nanometers