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Perception Block 9 > Photometry > Flashcards

Photometry Flashcards

1
Q

Power produced by a source of EM radiation

A

Radiometry

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2
Q

Deals with the effect that the radiation has on the visual system

A

Photometry

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3
Q

What is the difference between radiometry and photometry

A

Radiometry does not take into account the “visibility” of the source

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4
Q

What is radiometry important for

A

Surgery

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5
Q

Describes the relative sensitivity of the eye to different wavelengths in the visible spectrum

A

Photopic luminosity curve, V(lambda), CIE luminosity function

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6
Q

What is the fundamental difference between photometry and radiometry

A

V (lambda)

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7
Q

At what wavelength is the eye most sensitive to

A

550

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8
Q

What does the photopic luminosity curve tell us

A

Certain wavelengths are mroe efficient at stimulating the visual system than other wavelengths of light

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9
Q

What is to be said about a blue light source at 10W, and wavelength of 400nm, and a red light source at 10W and 600nm wavelength?

A

Radiometrically equal but photometrically different

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10
Q

How many lumens a certain light source produces per watt

A

Luminous efficiency

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11
Q

Equation for luminous efficiency

A

LE x (680 lumens/W) x W

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12
Q

Total amount of light that emerges in all directions from the source

A

Luminous power

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13
Q

What is the unit for luminous power

A

Lumens

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14
Q

Light power produced in a given direction by a point source

A

Luminous intensity

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15
Q

What is the unit for luminous intensity

A

Candela (cd)=1 lumen/steradian

Steradian is cone

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16
Q

The amount of light coming off of a surface in a specified direction

A

Luminance

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17
Q

Unit of luminance

A

Candeal/square meter (cd/m2)

-nits and apostilb

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18
Q

The luminous power that falls on a surface

A

Illuminance

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19
Q

Unit of illuminance

A

Lumens/square meter (on/m2)=lux

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20
Q

Total light power produced by a source

A

Luminous power

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21
Q

Radiometric equivalent to luminous power (lumens)

A

Radiant power (joules/second or Watts)

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22
Q

Light power produced in a solid angle by a point source

A

Luminous intensity

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23
Q

Radiometric equivalent of luminous intensity

A

Randiant intensity (watts/steradian)

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24
Q

Radiometric equivalent of luminance

A

Radiance (watts/steradian/square meter)

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25
Q

Radiometric equivalent of illuminanace

A

Irradiance (watts/square meter)

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26
Q

As a surface is moved away from a point source, the number of lumens falling on it decreases with the square of the distance, resulting in a decrease in its illumination

A

Inverse square law
E=I/d^2

E=illumination falling on the surface
I=intensity of the point source
D=distance from the point source to the surface

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27
Q

Criterion for luminous intensity with different surfaces

A
  • how much light illuminates the surface
  • distance from the light source
  • reflectance of the surface
  • tilt of the surface relative to your line of sight
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28
Q

Reflects all the light in one direction. In this case, the angle of reflection=the angle of incidence. These surfaces appear shiny like a mirror or polished chrome

A

Speculation reflection

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29
Q

Scatter reflected light in all directions. These surfaces appear matte or dull. Examples include a wall painted with matte paint or a non-glossy piece of paper

A

Diffuse reflector

30
Q

Relationship between illuminance and luminance for a lambertian surface

A

If a 100% reflecting (pure white) lambertian surface is illuminated by 1.0 lux, it will produce a luminance of 1/pi nits or 1 apostilb.

31
Q

One apostilb

A

1 aps= 1/pi candelas/m2=1/pi nits

32
Q

When does apostilb apply

A

Only to lambertian surfaces

33
Q

Asb=

A

1/ (cd/m2)

34
Q

This quantity is the amount of light falling on the retina

A

Retinal illumination

35
Q

What is the unit for retinal illumination

A

Roland’s (Td)

36
Q

What is a troland (retinal illuminance) directly proportional to?

A

Object illuminance and pupil area (not diameter)

37
Q

Formula for retinal illuminance

A

Td=(luminance of the object in nits)x (pupil AREA in mm2)

38
Q

Why does retinal illuminance remain constant for any object distance?

A

While the illuminance, that is, the amount of light entering the eye decreases with the square of the distance, the area of the retinal image also decreases with the square of the distance. The retinal illuminance therefore remains constant

39
Q

What what wavelengths do incandescent lights perform better

A

Larger

40
Q

At what wavelengths do fluorescent lights perform better?

A

Erratic, not able to tell

41
Q

At what what wavelengths do LED lights perform better?

A

Blue spectral region

42
Q

A theoretical construct that is convenient for describing sources of electromagnetic radiation, including light sources

A

Blackbody radiator

43
Q

As temperature of blackbody radiator increases

A

The peak wavelength decreases and the area under the spectral distribution curve, which represents power, increases

44
Q

What color is at 2000K

A

Yellowish

45
Q

What color is at 10,000K?

A

White/blue

46
Q

As temperature increases on a blackbody radiator what happens to wavelength

A

Decreases

47
Q

A blackbody radiator with a temperature of 2000K has most of its power concentrated at _____ wavelengths

A

Longer

48
Q

A blackbody radiator with a temple rather of 10000K has its power concentrated at _____ wavelengths

A

Shorter

49
Q

Warm white

A

2000K-3000K

50
Q

Cool white

A

3100K-4500K

51
Q

Daylight

A

4600K-6500K

52
Q

Advantage to higher color temperature

A

We see better at night with 4000K LEDs than with 2700K high pressure sodium bulbs

53
Q

Disadvantages to higher color temperature

A

3 times more scattering at 465nm than at 600nm. Rayleigh scattering, causing more area of glare

54
Q

What can high color temperature cause

A

Discomfort glare (annoyance glare)

55
Q

Who is most affected by annoyance glare from higher color temperatures

A

Presbyopia and cataract patients

56
Q

Cone, or daylight sensitivity peaks at ___

A

555nm

57
Q

Rods, or night time sensitivity peaks at ____

A

507nm

58
Q

The peak luminosity of photopic vision is _____ at peak response of 555nm

A

680 lumens/W

59
Q

The peak luminous efficacy of scotopic vision is _________ at a peak response of 507nm

A

1700 lumens/W

60
Q

What is the eye more sensitive to at mesopic and scotopic conditions

A

Shorter wavelengths or higher color temp

61
Q

May absorb/reflect some wavelengths that are incident upon it

A

Colored filters

62
Q

A filter that passes only a certain specified spectral band of light, such as only pure green (550-555)

A

Bandpass filters

63
Q

A filter that passes only a narrow spectral band of light

A

Narrowband filter

64
Q

A filter that passes only a broader spectral band of light

A

Broadband filters

65
Q

A filter that transmits long wavelengths of light, but not shorter wavelengths

A

Long-pass filter

66
Q

A filter that produces a very narrow band of light based on the interference principle of light

A

Inference filters

67
Q

Color filters subtract light. Two filter combos in sequence transmit less light than either one by itself

A

Subtractive color mixtures

68
Q

Light from different filters summed. Light is projected through two different color filters and combined on a screen to produce an additive mixture. It has more light that either one by itself

A

Additive color mixtures

69
Q

Transmits all wavelengths equally, and minimizing color distortion

A

Natural density filters

70
Q

How are natural density filters specified

A

By their optical density

OD=log (1/T)

T=transmittance of the filter

71
Q

Application of neutral density filters

A

used in combination with high pass filters that block UV radiation in sunglasses to minimize color distortion for patients who have anamalous color vision

Perception Block 9 (5 decks)

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