Visual Perception Flashcards
Define radiometry.
The science of the measurement of electromagnetic radiation
NOTE: both visible and non-visible light
What are the units of radiometry?
- Radiant flux
- Radiant intensity
- Radiance
- Irradiance
Which unit of radiometry is this describing?
- A measurement of ALL light waves coming off a light source
- Units: Watts (joules/sec)
Radiant Flux
Which unit of radiometry is this describing?
- Total measure of total light (possibly from multiple steradians) on a surface*
- Units Watts/m^2
Irradiance
Which unit of radiometry is this describing?
- Power per solid
- Power output of a (point) light source in a given direction (solid angle)
- Units: Watts/steradian
Radiant Intensity
NOTE: steradian is a 3D, cone-shaped measurement of light, w a spherical cap coming from a point source (a sphere is 4pi steradians
Solid angle is the angle of light coming from the point source that forms the point of the steradian cone
Which unit of radiometry is this describing?
- Radiant intensity per unit projected area of an (extended source)
- Area of light in one steradian incident on a particular area
- Units: Watts/m^2(steradian)
Radiance
What is the science of the measurement of the eye’s response to (or perception of) electromagnetic radiation? I.e. ONLY visible light?
Photometry
What are the units of photometry?
- Luminous flux
- Luminous intensity
- Luminance
- Illuminance
Which unit of Photometry is this describing?
- Luminous intensity per unit projected area of an (extended source)
- Area of the visible light in ONE steradian incident on a particular area
- Unit: cd/m^2 (nit OR ft-lambert)
Luminance
Which unit of Photometry is this describing?
- Power output of a light source
- Measurement of ALL visible light emitted from a source
- Unit: Lumens
Luminous Flux
Which unit of Photometry is this describing?
- Power output of a point light source in a given direction (solid angle)
- A measurement of visible light in ONE steradian
- Unit: Lumens/steradian (Candela, cd)
Luminous intensity
Which unit of Photometry is this describing?
- Luminous flux incident on an object’s surface
- Total measure of total visible light (possibly from multiple steradians) on a surface
- Unit: Lumens/m^2 (lux)
- English: Foot-candle (ft-cd)
Illuminance
Lumens is the unit for what?
Luminous flux
Candela is the unit for what?
Luminous intensity
“a Candle is INTENSE”
NOTE: Luminous intensity is also Lumens/steradian
Candela/m^2 OR nit OR Foot-Lambert (fL) are the units for what?
Luminance
Lux or Lumens/m^2 or Foot-candle are the units for what?
Illuminance
At 555nm how many lumens are there for both scotopic and photopic systems?
683 lumens
On plot: 1 lm/W @ 555 nm
Find the relative luminance efficiency for the given wavelengths on the plot & multiply by 683 lm/w
Multiply by given watts for each wavelength
Add together
What is the equation to convert illuminance to luminous intensity?
Intensity (I) = Distance (D)^2 x Illuminance (E)
I=D^2 x E
Describe Retinal illuminance and the equation
Its the amount of light getting into the eye
Unit:
Trolands (td)
Equation:
T = L x A
Trolands = Luminence (cd/m^2) x Pupil Area (mm^2)
What’s the equation Inverse square law.
E = I/d^2
E = Illuminance (lux; lumens/m^2; ft-cd) I = Intensity (cd) d = distance (m)
Describe the concept of the inverse square law
As the (d) INCREASES, the same amount of light is dispersed over a proportionally larger area …. therefore, DEC intensity of light!
NOTE: smaller point light sources make this law work BETTER
NOTE: only works if there is NO additional reflected light
Describe the Cosine Law of Illuminance
Illuminance DECREASES with the cosine of the angle from normal
I.e. as the surface is TILTED AWAY from being perpendiculat to the light source, the illuminance of the surface DECREASES!!! (basically most illuminance is 90 degrees from surface)
Equation for Cosine Law of Illuminance?
E = (I/d^2) x cos(theta)
What is a special kind of surface whose luminance does NOT vary with the angle at which it is viewed (i.e. cosine law of illuminance does NOT apply)
Lambertian diffuser
EXAMPLES: matte paper, unfinished wood
With perfect reflectance (r=1.0) all light that falls on a surface is reflected
Illuminance at the surface would equal the measurement of luminance equals the measurement of the luminance from the surface (i.e. same amount of light is incident on the surface and reflected off the surface)