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Optics > L-26 > Flashcards

L-26 Flashcards

1
Q

What do the 8 divisions deal with of The International Commission on Illumination (CIE)?

A
  1. Vision and Colour
  2. Measurement of Light and Radiation
  3. Interior Environment and Lighting Design
  4. Lighting and Signalling for Transport
  5. Exterior Lighting and Other Applications
  6. Photobiology and Photochemistry
  7. General Aspects of Lighting (Awaiting allocation)
  8. Imaging Technology
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2
Q

What is the 1st division vision and colour about ?

A

Concerned mainly with standards in photometry, colorimetry, colour rendering, visual performance and visual assessment of light and lighting

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3
Q

What is the 2nd division Measurement of Light and Radiation about?

A

Concerned with detectors and measurement of radiation from ultraviolet to infrared

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4
Q

What is the 3rd division Interior Environment and Lighting Design about?

A

Concerned with lighting in buildings and their environment

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5
Q

What is the 4th division Lighting and Signalling for Transport about?

A

Concerned mostly with lighting and visual signalling and information requirements of transport and traffic

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6
Q

What is the 5th division of Exterior Lighting and Other Applications about?

A

The design of lighting for pedestrian and other urban areas, security lighting, flood lighting, etc

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7
Q

What is the 6ht division of photobiology and photochemistry about?

A

Effects of optical radiation on biological and photochemical systems

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8
Q

What is the 8th division of imaging technology about?

A

Processing and reproduction of images, using all types of analogue and digital imaging devices, storage media and imaging media

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9
Q

What are the key achievements of this commission ?

A

1924
-CIE established the standard photopic observer defined by the spectral luminous efficiency function V(λ)

1931

  • Standard illuminants A, B, and C.
  • CIE 1931 colour matching functions
  • CIE 2° standard observer
  • CIE established the XYZ colour space

1951
-CIE established the standard scotopic observer
defined by the function V’(λ).

1964

  • CIE 10° standard observer
  • 10o colour matching functions
  • CIE standard illuminant D6500 (D65)
  • Correlated colour temperature

1976
-CIE developed the CIELAB and CIELUV colour spaces

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10
Q

Why is black body radiator important ?

A

determined virtually entirely by its temperature

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11
Q

What does the BB radiator follow ?

A

Plancks law

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12
Q

So what is the BB determined by ?

A

its output is totally determined by its temperature (K)

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13
Q

The Black-Body Radiator equation ?

A

Me𝝀 = 2(pi)hc^2𝝀^-5(e ^hv/kT - 1)^-1

temp in Kelvin

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14
Q

What can you do for any absolute temperature ? (shown in graph of slide)

A

plot the relative emittance , amount of light emitted per unit area of the black body source as a function of wavelength

  • Then can see the BB source, which approximates very well a tungsten lamp, a heated filament lamp, produces very little light with a peak in the IF part of spectrum at low temperature
  • But then this peak emission wavelength shifts towards low wavelengths as the temp increases
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15
Q

What happens when you go from a low to high temperature in BB radiator ?

A
  • you have a massive increase in the radiant flux output per unit are of the BB source.
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16
Q

What does a low temperature source produce in the short wavelength region of the spectrum ?

A

barely any light

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17
Q

What does the blue short wavelength part produce ?

A

the total radiant flux as well as the output in the blue wavelength part of the spectrum is much higher as the temperature increases

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18
Q

Why is it convenient to equally normalise the BB sources at different temps?

A

so that they all have the same values at about 555nm here. ( shown in 3rd graph)

19
Q

How much light is there at a low temperature ?

A
  • have lot of light in the long wavelength part of the spectrum
  • with very little light in short wavelength part of spectrum .
20
Q

How much light is there at a high temperature ?

A

-more light in short wavelength part of the spectrum that the long wavelength part of the spectrum.

21
Q

What does the function in the BB equation allow to predict?

A

the function allows to predict the spectral radiant flux emitted by the BB source
-Makes it extremely easy to compute certain things about the BB source

22
Q

What happens if you see the peak spectral output starts at a long wavelength ?

A

becomes shorter as the temp increases and shorter.
-we can take the derivative of this function and establish the turning points (the wavelength at which the turning points take place) - which turns out the be directly proportional to the reciprocal of temp

23
Q

What is the wavelength of maximum output?

A

directly proportional to 1/ T

24
Q

Why is this important ?

A

it provides the basis for the MIRED (Micro Reciprocal Degrees) scale or sources as well as filters
- Mireds = 106/T

25
Q

What happens if the temperature is high?

A
  • so if the temp is high the mired value will be small
  • so a small value corresponds to a large output of the short wavelength part of the spectrum
  • in large mired value coressponds to small temp which means a larger output in the long wavelength part of the spectrum.
  • Tungsten (2854 K) = 350 Mireds; D65 (6500 K) = 154 Mireds
26
Q

What can both filters and sources can be calibrated from ?

A

Both filters and sources can have a MIRED value.

  • they can be calibrated in MIRED - can shift from one mired value to another mired value by adding or subtracting the value of a particular filter
  • The just noticeable difference between two sources is based on their MIRED values.
  • The smaller the MIRED value, the greater T and hence the ‘bluer’ the colour appearance of the source
27
Q

What are other parameters which you can compute from the BB formula for the spectral radians output ?

A
  • the total power emitted unit area of the BB source
28
Q

What happens in the total power output ?

A

total radiant flux output a unit area of the BB source is directly proportional to the 4th power of the temp

  • it is determined by the temperature of the source
  • MTotal = (onstant) T4, where constant = 5.6703x10-8 watts m-2 K-
29
Q

What happens when running the source at higher temperature is very difficult ?

A

because the heated tungsten (which produces the light) starts evaporating which is why need to use tungsten halogen lamps where eh gas itself under pressure push back the evaporated tungsten atoms back into the filament so that it extends the light of the filament

  • this is what happens when the temp is 3200 where you get a specific amount of short wavelength light and relatively large amount of radiant flux.
  • The spectral power distribution of most tungsten light sources can be approximated by a BB source at a given temperature. A high temperature tungsten-halogen lamp (T~ 3200K), for example, approximates a BB radiator and its maximum output corresponds to ~ 906 nm.
30
Q

What does the sun radiation peak at ?

A
  • has a peak emission wavelength of ~ 527 nm (where the spectral responsivity of the human eye is high!).
31
Q

What is the temperature of the surface of the sun ?

A
  • The sun’s radiation (which approximates a BB at ~ 5500 K)
  • eye has evolved with a spectral responsibility that covers very well the region over which the light emitted by sun is greater, is larger.
32
Q

What are the standard light sources / CIE illiuminants?

A

have been introduced to be able to be compared against these standards
-the output of other practical sources such as The selected illuminants act as standards for tungsten, daylight, fluorescent and special light sources

33
Q

What is a CIE illuminant is defined by?

A

its spectral power distribution (i.e., relative radiant flux versus wavelength)

34
Q

What are the other CIE illuminants?

A

CIE Illuminant A.
BB (Planckian Radiator, representative of tungsten filament lamp) at a temp of 2856K
CCT = 2856 K;
CIE (x,y): 0.447, 0.407 S/P -
- (Scotopic/Photopic ratio) = 0.566 - it is computed by taking the spectral emissions of the CIE illuminant A and calculating the coresponsing luminous emittance for both scoptic/photopic vision and the ratio gives the S:P
-the S:P - is not very effieicnet for scoptic vision because it does not emit a large amount of middle wavelength than blue light
-produces a lot of long wavelength red light
-the chromatic co-ordinates which specific the colour of source are definitely in the long wavelength region of chromatic diagram

35
Q

What is another CIE illuminant ?

A 
CIE Illuminant D65. 
-to approximate more closely Standard daylight (average noon daylight from the northern sky). at 6500K
CCT = 6500 K;
- CIE (x,y): 0.313, 0.329 
-S/P = 0.99
36
Q

What are the several different CIE illuminants ?

A

-D50.
-This ‘daylight’ illuminant is the reference for the printing and graphic arts industry
-CIE Illuminant C. Introduced in 1931, CCT =
6774 K (Average daylight from the northern sky). Produced by filtering tungsten illuminants, hence low UV content.

37
Q

How can we generate a BB?

A

at any temp

38
Q

What are the other CIE illuminants of fluroscnet lamps?

A
  • CIE F2. Cool White Fluorescent - CCT = 4230, Lamp designed for typical office lighting
  • CIE F7. Broad Band - Fluorescent (BBF). CCT = 6500
  • CIE F11. Efficient TL84, tri- band (CWF). fluorescent lamp used inwarehouses, etc. CCT = 4000.
39
Q

What is the spectral power distribution of these phosphorus based fluorescent lamps ?

A

very spiky.

  • however the illuminants itself is equivalent to the BB at a correlated colour temp of 4000K
    -because the signals generated in the four photoreceptors in the eye depend on the spectral reflectance of objects and on the spectral power distribution of the
    illuminant:
    -use these illuminants to illuminate objects in the surround
    -there are many standard reflecting patches which have known spectral refelectance - (diff colours)
    -there are also achromatic patches which affect all wavelengths by the same amount.
    -we can now compute the luminance value of each of these using either the CIE photopic spectral illuminance efficiency function or the CIE scotopic.
    -
    ***** ??????
40
Q

How can we calculate contrast

A

by the luminance signals

41
Q

How can we calculate contrast which is important in human vision ?

A

by the luminance signals

42
Q

What is the contrast of the achromatic stimuli and all of achromatic test charts ?

A

ddoes not change as you change either the amount of light you put onto the test chart of its spectral composition
-you can use tungsten or daylight and contrast of these patches will remain the same.

43
Q

What happens in the contrast of the colour patches ?

A

depends strongly on the type of illumination t one employes

-this is the reason why they are made form achromatic stimuli

44
Q

What is an advantage of achromatic targets and discharge. ?

A
  • the contrast is invariant in with changes in the spectral power distubution of the illuminant or with changes in the illuminance level onto the test chart.
    (-things which changes an illuminants the changes in level of illumination dont change the contrast in optotypes used to asses vision)

-However this is not the case when you are dealing with coloured stimuli

Optics (34 decks)

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