Radiometry/ Photometry Flashcards
visual acuity testing is specified to have a minimum chart luminance of ______
85 cd/m^2
what is radiometry?
the science of the measurement of electromagnetic radiation
what is photometry?
the science of the measurement of the eye’s response to (or perception of) electromagnetic radiation
what is the total power output of a light source measured in watts (joules/second)
radiant flux (aka radiant power)
units of radiant flux (radiant power)
Watts (Joules/Second)
what is the power output of a point (light) source in a given direction (solid angle), measured in watts/steradian
Radiant Intensity
units of radiant intensity
watts/steradian
a sphere contains how many steradians
4 pi steradians
what is the radiant intensity per unit projected area of an extended source, measured in watts/ square meter steradian
radiance
units of radiance
watts / square meter steradian
what is the radiant flux incident on an object’s surface, measured in watts/ square meter
irradiance
units of irradiance
watts/ square meter
what is the energy received per unit area of irradiated surface, measured in J/m^2
radiant exposure
UV exposure limit
0.003 J/cm^2
in a day for cornea/skin
visible light exposure limit
3 J/cm^2
IR exposure limit
3000 J/cm^2
what is the total power output of a light source, measured in lumens
luminous flux (luminous power)
a ____ nm light is the ‘brightest’
555 nm
peak for scotopic conditions is _____ nm
507 nm
why is 555 nm light the ‘brightest’?
it has the most ‘luminosity’ or highest luminous efficiency for photopic conditions
there are ___ lumens per watt at 555nm
683 lumens/watt
for scotopic functions, ____ lumens/watt at 507nm
1700 lumens/watt
what is the power output of a point light source in a given direction (solid angle), measured in lumens/steradian
luminous intensity
units of luminous intensity
lumens/ steradian
candela, cd
what is the luminous intensity per unit projected area of an extended source, measured in candelas/ square meter
luminance
units of luminance
- candelas/ square meter
- nit
- foot-lambert (fL)
10^-6 to 10^-1 cd/m^2 is for ______ vision
scotopic
10^-1 to 10^1 cd/m^2 is for _______ vision
mesopic
10^1 to 10^7 cd/m^2 is for _______ vision
photopic
the eye operates over a tremendous range of light levels, about ___ log units
12 log units
what is luminous flux incident on an object’s surface, measured in lumens/square meter (lux)
illuminance
units of illuminance
- lumens/ square meter
- lux
- lumens/ square foot (ft-cd)
1 fL = ___ cd/m^2
3.43
1 fc = _____ lux
10.76
_____ is defined (arbitrarily) as an amount of light getting into the eye
retinal illuminance
units of retinal illuminance
trolands (td)
formula for retinal illuminance calculations
trolands = luminance (cd/m^2) x pupil area (mm^2)
what is a special kind of surface whose luminance does not vary with the angle at which it is viewed
- lambertian diffuser
- cosine diffuser, perfect diffuser
how does luminous intensity change with distance?
it does not change with distance
how does luminance change with distance?
luminance does not change with distance
how does luminance of an extended source change with viewing distance?
it doesn’t
brightness constancy
how does luminance of an extended source change with viewing distance? (for the same angular subtense of view)
the viewed area (projected area) of the stimulus decreases (linear dimensions) at sorted distances
