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Visual Science > Visual Science: Photometry 1: Chapter 4 > Flashcards

Visual Science: Photometry 1: Chapter 4 Flashcards

1
Q

Electromagnetic Spectrum

  1. Visible Radiation: Wavelength range?
A
  1. 400 nm to 700 nm
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2
Q

Define Radiometry

A

Power produced by a source of electromagnetic radiation, irrespective of its effect on vision

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3
Q

Define Photometry

A

Deals with the effect that this radiation has on the visual System (radiometry)

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4
Q

Electro-magnetic Radiation

  1. How do we calculate Frequency of Light?
A
  1. v = c/lambda

v = frequency of light

c = speed of light

lambda = wavelength of light

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5
Q

Amount of Energy in a QUANTUM of light is given by what relationship? (eqn)

A

E = hv

E = energy per quantum

h = planck’s constant (6.626 x 10^-37 J/Hz)

v = Frequency

of

E = hc/lambda

c = speed of light and lambda = wavelength

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6
Q
  1. how much energy per quantum in UV light is there?
    a. What happens when it’s absorbed by the skin?
  2. Excessive exposure to what type of Radiation will cause a GLASS BLOWER’s CATARACT?
  3. Why is LONGER WAVELENGTH Radiation not visible?
A
  1. A LOT
    a. can cause a lot of cellular damage, including mutations that can lead to malignancy
  2. to Near-Infrared Radiation (1450 nm)
  3. Because it’s ABSORBED by the RETINAL PHOTOPIGMENTS
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7
Q
  1. What’s the basic unit of Photometry?
    a. What is it a measure of?
  2. What is Luminous Power used to specify?
  3. Certain wavelengths are more efficient at what?
A
  1. The LUMEN
    a. Measure of Luminous Power
  2. The TOTAL AMT of Light that EMERGES in all directions from a source
  3. at Stimulating the VISUAL SYSTEM than others
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8
Q
  1. How many Lumens per Watt is there at 555 nm?
  2. How would you figure out lumens at other wavelengths?
  3. What is the WATT?
  4. What is Luminous Power used to specify?
A
  1. 680 Lumens (the peak of the curve)
  2. Look at the curve, and see what the Luminous Efficiency is, then multiply that by the Peak (680 lumens) and you will get the Lumens/W for that specific wavelength!
  3. It’s the BASIC UNIT of RADIOMETRY, and is a measure of RADIANT POWER
  4. The Total Amt of light that emerges in ALL DIRECTIONS from a SOURCE
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9
Q

Abney’s Law of Additivity

  1. What does this Law state?
  2. Why does this work?
A
  1. That the PHOTOMETRIC System is ADDITIVE!!

2. Because most Objects EMIT or REFLECT a mixture of several different Wavelengths.

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10
Q

Luminous Intensity

  1. What does it refer to?
  2. What does Luminance Quantify?
    a. What’s the Perceptual Attribute associated with Luminance?
  3. What are the units for Luminance?
A
  1. The number of Lumens Produced in a Given direction by a Point light source
  2. The Amt of light coming off a surface (like a piece of paper) and in a SPECIFIED DIRECTION
    a. BRIGHTNESS
  3. CANDELAS/Area of light source. (cd/m^2) and foot lamberts
    * 3.426 cd/m^2 per foot-lambert
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11
Q

Luminous Intensity

  1. If the ratio of Candelas to Image Surface area remains CONSTANT, what does this mean?
  2. What happens as Distance INCREASES?
A
  1. Luminance and Brightness DONT CHANGE
  2. Area of the image (retinal image or one formed on a luminance probe) DECREASES at the SAME RATE that the NUMBER of CANDELAS does that’s contained w/in the image.
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12
Q

Luminous Intensity

  1. What’s the unit for Luminous intensity?
    a. What is that defined as?
  2. What is a Steradian?
A
  1. Candela (cd)
    a. 1 Lumen per Steradian
  2. (Sr) is a SOLID ANGLE (It’s a CONIC Section of a SPHERE)
    * omega = A/r^2
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13
Q

Illuminance

  1. What does it refer to?
    a. Units?
    b. Number per foot-candle?
A
  1. Luminous Power that falls on a Surface
    a. Lumens per square Meter (LUX) and lumens per square foot (foot-candles)
    b. 10.76 lux per foot-candle
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14
Q

*Look at chart on Page 69 of the book

A

Pg 69 of the book

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15
Q

illuminance

  1. Is analogous to rain. Why?
  2. Which will have HIGHER Luminance? A White piece of paper, or a black book?
A
  1. Intensity of rain is not affected by the surface on which it falls, the illuminance is not affected by the surface on which the light falls.
    * Greater the density of raindrops (lumens), the harder it’s raining (greater the illuminance)
  2. a white piece of paper, because it REFLECTS MORE LIGHT!!
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16
Q

Radiometric Units: Radiometric Equivalents

  1. Radiant Power
  2. Radiant Intensity
  3. Radiance
  4. Irradiance
A
  1. Luminous Power
  2. Luminous Intensity
  3. Luminance
  4. Illuminance
17
Q

Cosine Diffusers

  1. What is a cosine diffuser?
  2. Luminance
  3. Illumination
  4. Eqn?
A
  1. Illumination of 1 lumen/ft^2, falling on a MATTE SURFACE w/a Reflectance Factor of 1, produces a Luminance of 1 Foot-Lambert.
  2. 1/pi candelas/ft^2 or 1 foot-lambert
  3. 1 lumen/ft^2
  4. L = rE

L = luminance in foot-lamberts

r = reflectance factor (nondimensional, no units)

E = illumination in foot-candles (lumens/ft^2)

18
Q

Inverse Square Law

  1. As a Surface is moved away from a point source, what happens?
    a. Eqn?
A
  1. # of lumens falling on it DECREASES with the SQUARE of the DISTANCE!! Causes a DECREASE in ILLUMINATIONa. E = I/d^2

E = Illumination falling on the surface

I = Intensity of the Point source

d^2 = distance from the Point source to the surface

E = (I/d^2)cos(theta)

E2 = E1 Cost(Theta)

E1 = Illumination falling on surface when it’s normal to light

E2 = illumination falling on the Tilted surface

19
Q

Retinal Illumination

  1. What’s the basic unit?
  2. Eqn?
  3. Why is this important to calculate?
A
  1. The TROLAND
  2. T = LA

T = retinal illumination in Trolands (td)

L = Luminance of the surface that’s viewed

A = Pupil Area

  1. Because if it’s specified in Trollands, then all subjects will have the SAME AMT of light falling on their retinas REGARDLESS of Pupil diameter
20
Q

Luminous Power

  1. Define
  2. Common Units
  3. Radiometric Equivalent and Units
A
  1. Total light power produced by a source
  2. Lumens
  3. Radiant power (Joules/second or Watts)
21
Q

Luminous Intensity

  1. Define
  2. Common Units
  3. Radiometric Equivalent and Unit
A
  1. Light power produced in a solid angle by a point source
  2. Lumens/steradian (Candelas)
    1 lumen/steradian = 1 candela
  3. Radiant Intensity (Watts/Steradian)
22
Q

Luminance

  1. Define
  2. Common Units
  3. Radiometric Equivalent and Unit
A
  1. Luminous intensity per unit projected area of an extended source
  2. Candelas/square meter (Foot-lamberts)
  3. Radiance (Watts/steradian/square meter)
23
Q

Illuminance

  1. Define
  2. Common Units
  3. Radiometric Equivalent and Unit
A
  1. Luminous Power falling on a surface
  2. Lumens/square meter or lumens/square foot
  3. Irradiance (watts/square meter)

Visual Science (8 decks)

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