Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Optics > L- 25 > Flashcards

L- 25 Flashcards

1
Q

what is the definition of radiance ?

A
  • the radiance of the source is defined as the intensity per unit area of the source in a given direction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is the first case for radiance ?

A
  • the direction of interest is perpendicular to the plane of the source
    L0= I0/A [ units: lm/sr/m^2]
L0= at o degrees with respect to the normal to the surface
I0= intensity
A= Area
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is case 2 for radiance ?

A
  • the direction of interest form an angle θ, wrt the source
  • Lθ= Iθ/[A cosθ ]
  • where θ represents the angle between the normal to the surface and the direction of interest
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

is Lθ ( radiance )independent of θ?

A
  • for majority of sources and surfaces the radiance doesn’t change with the direction of measurement
  • radiance is constant and independent of the direction of measurement
  • this means that visually the source on the surface appears equally bright from whatever angle it is viewed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

how does Iθ have to change with the angle of measurement to ensure that Lθ remains constant?

A
  • if Lθ is independent of θ, then Iθ must be equal I0 cos θ
  • Lθ=L0 [ constant ]
  • Iθ= I0 cos θ
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what is the definition for a Lambertian source or surface?

A
  • the intensity of the source or surface is always proportional to the cosine of the angle between the direction of measurement and the perpendicular to the surface
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what is a formula of Lambertian surfaces ?

A
  • total light flux emitted by a lambertian source= πLA
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is the light flux formula ?

A
  • the amount of light which this surface receives in the first place will equal to the illuminance level or irradiance level that fall onto to the surface multiplied by the area of the surface
  • A x E {lm}
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is the flux radiated by the surface if the reflectance of the Lambertian surface is R?

A
  • if the reflectance of the Lambertian surface is R, the flux radiated by the surface equals R x A x E
  • L=RE/π
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what is the radiance of the luminance of a surface?

A

the radiance of the luminance of a surface is its reflectance x luminance level/π
- L= RE/π

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what is the photopic vision ?

A

vision is mediated largely by cones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

where does maximum luminous efficiency occur in photopic vision ?

A

the maximum luminous efficiency occurs at 555nm and is equal to 683 lm/ watt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

how can we calculate the amount of luminous flux in photopic vision?

A

weighting radiant flux by the sensitivity of eye and multiplying by 683

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is scotopic vision ?

A

vision mediated largely by rod photoreceptors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

where does the maximum luminous efficiency occur in scotopic vision?

A

the maximum luminous efficiency occurs at 510 nm and is equal to 1700lm / watt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what are the equivalence of radiometric and photometric quantities?

A
  1. radiant energy (J) = photometric energy (lm s)
  2. radiant flux (J/s or watts) = luminous flux (lm)
  3. radiant emittance ( w/m^2) = luminous emittance (lm/m^2)
  4. irradiance (W/m^2) = illuminance (lm/m^2)
  5. radiant intensity (W/sr) = luminous intensity ( lm/sr)
  6. radiance ( W/sr/m^2) = luminance ( cd/m^2)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

how to convert from radiant flux to luminous flux ?

A
  • radiant flux multiplied by the sensitivity of the eye for every wavelength of interest
18
Q

what is a filter/light modulator ?

A
  • a modulator or filter is any material or device which attenuates or changes this beam
  • the change can be either in intensity or spectral content
19
Q

how do we find the reflectance of a particular wavelength ?

A
  • we eliminate the test chart with light, certain amount of radiant flux is put on the surface of test chart and some of it is returned back
  • the amount returned divided by the amount of light which falls on the surface gives us the reflectance about particular wavelength
20
Q

what is transmittance ?

A

at any wavelength, the ration of the radiant flux transmitted and the incident flux on the surface of the filter is known as its transmittance

21
Q

what is reflectance ?

A

the ration of the reflected flux to that incident onto a sample is known as the reflectance

22
Q

what are neutral density filters/ test charts?

A

they have a spectral absorption that is independent of wavelength over the spectral range of interest ( usually the visible spectrum )

23
Q

what is the term filter used to refer ?

A

the term filter is used to refer to sheets of coloured glass or gelatine, interference filters, liquid filters and neutral density filters

24
Q

what is the transmittance of a filter or the reflectance of an object expressed as ?

A

the transmittance of a filter or the reflectance of an object is often expressed in log units
Log [T] or log [R] and described as optical density

25
Q

what does higher optical density mean ?

A

higher optical density = less light is reflected from the surface

26
Q

what is formula for OD(λ)?

A

OD [ λ ] = -log10 T [λ]

T [λ] = 10^-0D(λ)

27
Q

what is formula for OD when light is reflected from a surface ?

A

OD [ λ ] = -log10 R [λ]

R [λ] = 10^-0D(λ)

28
Q

how can we describe the transmittance of filter ?

A

decimal
percentage
optical density

29
Q

what does greater pigment mean ?

A

the greater the pigment , the greater the absorption , the higher the optical density and the smaller the transmittance

30
Q

what happens to light level on retina ?

A
  • depends on how large the image of the source is in the plane of the pupil
  • when we reduce light level on the retina the pupil size would increase, the amount of light that would end up on retina also increases
31
Q

what is integrated filter transmittance ?

A

a measure of the total radiant or luminous flux transmitted by the filter

32
Q

what are neutral density glasses ?

A

don’t change relative spectral composition of light which is transmitted
colour of light will not change

33
Q

how to work out radiometric transmission factor ?

A

total radiant flux that comes out passes through lens and comes out from the lens multiplied by spectral transmittance of the filter divided by total radiant flux that falls onto the filter

34
Q

how to work out photometric transmission factor ?

A

total luminous flux which passes through and is transmitted by filter divided by luminous flux incident on the filter

35
Q

what do the photometric transmission factor and radiometric transmission factor depend on ?

A

both depend on the spectral transmittance of the filter and the spectral power distribution of the illuminant

36
Q

how should a test chart be illuminated ?

A
  • test chart is illuminated with source of light
  • we try to achieve uniform illumination over the test chart so both letter and adjacent background receive same amount of luminous flux
37
Q

how to work out the contrast of the letters ?

A

a spectrally neutral test chart is illuminated uniformly and our task is to work out the contrast of the letters in terms of the optical density of the uniform background (ODB0 and that of the letters ( ODL)

38
Q

what is luminance of background proportional to ?

A

luminance of background is proportional will be proportional to the amount of light that we put onto background multiplied by the reflectance

39
Q

what is luminance of letter proportional to ?

A

luminance of letter is proportional to the amount of light on letter multiplied by reflectance of letter

40
Q

what is contrast independent to ?

A
  • contrast is independent of amount of light put onto the test chart
  • contrast independent of the spectral composition of the light

Optics (34 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions