Lecture 1 - Photometry, Radiometry Flashcards
1
Q
Is radiometry objective or subjective?
A
Objective
2
Q
Power produced by EMR; Doesn’t take into account visibility
A
Radiometry
3
Q
Is photometry subjective or objective?
A
Subjective
4
Q
Effect that radiation has on visual system; Perception - light bright enough or not?
A
Photometry
5
Q
What is the fundamental difference?
A
The multiplication of radiometry and photometry = V(wavelength)
6
Q
What is the luminous efficiency?
A
How bright/efficient the light is
7
Q
Does the wavelength of light matter when talking about the efficiency of it?
A
Yes. Some wavelengths of light are more efficient at stimulating the visual system than others
8
Q
What does the photopic luminosity curve show?
A
Visible spectrum to different wavelengths
9
Q
Example:
At 550 wavelength, what color is the human eye most sensitive to?
A
Green
10
Q
______ can be equal, but ______ different
A
Radiometry (power)
Photometry (wavelength)
11
Q
Example:
At 400 nm wavelength, P = 10W Blue light
At 600 nm wavelength, P = 10W Red light
What will you see?
A
You’ll see red, but not blue because blue = 0 lumens (or Watts) and red = 4216 lumens (or Watts)
12
Q
Example:
400 nm @ 10W is equal to how many lumens?
A
(Luminous efficiency) x (max visual system = lum eff = 680 lumens/W) x (Power in watts) 0 x (680) x (10) = 0 lumens
13
Q
Example:
600 nm @ 10W is equal to how many lumens?
A
(Luminous efficiency) x (max visual system = lum eff = 680 lumens/W) x (Power in watts)
0.62 x (680) x (10) = 4216 lumens
14
Q
Photometry units of luminous power and direction of light
A
Lumen (lm)
All directions
15
Q
Photometry units of luminous intensity and direction of light
A
Candela (cd) = 1 lumen/steradian
Given direction
16
Q
Photometry units of luminance and direction of light
A
Candela/square meter (cd/m^2) = nit/apostilb (asb)
Coming off surface
17
Q
Photometry units of illuminance and direction of light
A
Lux = lumens/square meter (lm/m^2)
Falls on surface
18
Q
What unit is radiance power in?
A
Watts
19
Q
As surface moves away, number of lumens falling on it decreases with square of distance and illumination
A
Inverse square law
20
Q
Equation to find Inverse Square Law
A
E = I/(d^2)
Illumination falling on surface = (intensity of point source)/(distance from point source to surface^2)
21
Q
What are the 4 things you need to know to figure out the amount of light that is, it’s brightness, the luminous intensity with different surfaces will depend on?
A
1) how much light ILLUMINATES surface
2) DISTANCE from light source
3) REFLECTANCE of surface
4) TILT of surface to line of sight (@ certain angle)
22
Q
A source with which of the following color temperatures will appear most red?
A
2000K
23
Q
The color temp of an incandescent bulb is 3300 degrees Kelvin. This means that:
A
The bulb’s spectral distribution matches that of a black body radiator whose temperature is 3300 K
24
Q
A neutral density filter transmits 50% of 450 nm light that is incident upon it. If 40 W of 550 nm are incident on the filter, how many Watts are transmitted?
A
20
25
The least amount of distortion is present with sunglasses made with what kind of filter?
Neutral density filter
26
Which of the following light sources has more energy concentrated in the blue region of the spectrum?
LEDs
27
A patient whose retina contains only rods (i.e., a rod monochromat) views the following four patches of monochromatic light: 440, 510, 555, and 565 nm. Each patch emits 20 quantral absorptions. Which is brightest?
510 because it's closest to 507 nm
28
Assume that the absorption of 10 quanta of 510 nm by an eye that contains only rods (i.e., the eye of a rod monochromat) results in vision. If the wavelength were 450 nm, how many quanta would need to be absorbed to produce vision?
10 quanta
| Question could also be read a little differently, so the answer could also be greater than 10 quanta
29
Your patient, a rod monochromat, has asked for advice regarding tinted lenses. You should advise a darkly tinted lens of which color?
Red
(Rods are more sensitive at lower wavelengths; the photochromatic interval curve is the difference between photopic and scotopic. Where they merge, it's at 0, and at 650 nm (red))
30
In the photchromatic interval curve, where is the difference between photopic and scotopic the least?
At 650nm (red)
31
Under scotopic conditions, a blue and yellow flower appear equally bright. Under photopic conditions, which flower will most likely appear brighter?
The yellow flower
| Photopic = 555 peak sensitivity is around the green/yellow mark
32
A patient has degenerative disease that has destroyed her cones. The expected visual acuity for this patient is closest to:
20/200 (her peripheral vision is still in tact for the most part, but her central vision is pretty much gone)
33
When foveally fixated by a person with trichromatic vision, a small target (0.5 degrees) of which of the following wavelengths will be least visible?
430 nm
| No blue cones in the fovea, up to 0.3-0.5 degrees eccentricity and no rods => have green and red cones
34
Under daylight conditions, a red and green surface looks equally bright. Compared to the green surface, the red surface most likely emits:
```
More energy
(Daylight = photopic sensitivity curve => need more quanta to be equal b/c it peaks at 555, and you are around 650, so you have to add more quanta to get up to the peak again)
```
35
Photopic and scotopic thresholds are most similar to each other for which wavelength?
```
650 nm
(Photochromatic interval b/w rods and cones at 650 nm = 0)
```
36
Which of the following classes of cones contributes least to the photopic spectral sensitive curve?
S-cones
| Blue cones are in much less amounts than red and green cones
37
What are the 2 types of reflective properties of a surface?
Specular reflector
| Diffuse reflector
38
What direction does light reflect in specular reflection?
In one direction (angle of reflection = angle of incidence)
39
What do specular reflector surfaces appear as?
Shine, like a mirror or polished chrome
40
What direction does light reflect in diffuse reflection?
In all directions
41
What do diffuse reflector surfaces appear as?
Matte or dull (not glossy)
| Ex: wall painted with matte paint, or a non-glossy piece of paper
42
If a 100% reflecting (pure white) lambert Ian surface is illuminated by 1.0 lux, what luminance will it produce?
Luminance = 1/3.14 (pi) nits
43
Units of illuminance
Lux = lumens/m^2
44
1 lux = how many nits after it hits a 100% reflector?
1/pi nits = 0.318 nits
45
One apostilb is equal to how many nits?
1/pi nits = 0.318 nits
46
When luminance is measured in apostilbs, what's the relationship between illuminance and luminance?
1 lux onto a 100% reflector surface gives off 1 apostilb (asb)
47
Equation for apostilb to nits
1 apostilb = 1/pi candelas/m^s (or 0.318 nits) = 1/pi nits
48
White surfaces reflect how much of the incident of light?
Nearly 100%
49
If a grey lambertian surface reflects 50% of the light, what would be the resulting luminance?
50%
50
When 1 lux of illluminance falls upon a grey lambertian surface that has 50% of reflectance, what is the luminance that comes off of the surface?
0.5 apostilb (1/2 reflectance)
51
The apostilb is the second unit for _____, and it applies only to _____ surfaces.
Luminance
| Lambertian
52
Finish this equation:
| Asb = ?
1/pi candela/m^2
53
Finish this equation:
fL = ?
(Foot-Lambert)
FL = 1/pi candela/ft^2
54
In retinal illumination, what is the quantity?
The amount of light falling on the retina
55
What 2 things tell what the illumination will be?
Luminance and pupil size
56
Units for retinal illumination?
Trolands (Td)
57
Formula for retinal illuminance
```
Td = (nits)(mm^2)
Troland = (luminance of the object in nits)x(pupil area in mm^2)
```
58
What is unique about retinal illuminance as the object distance changes?
The retinal illuminance remains constant for any object distance
59
What is the difference for object distance between retinal illumination and the inverse square law?
RI: illumination remains constant for any distance
ISL: if distance to screen increases, then luminance decreases
60
If illumination entering the eye decreases with the square of the distance, how can retinal illumination remain constant for all distances?
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.
61
Suppose you are looking at a piece of paper in bright sunlight. What would the retinal illuminance be for the image of that paper on your retina, assuming the luminance of a piece of paper in sunlight is about 10,000 nits and your pupil diameter is equal to 2.0 mm?
Pupil area = (pi)r^2 = (pi)(1^2) = 3.14592 mm^2
| (Lum nits)x(pupil mm^2) = (10,000 nits)x(3.14592 mm^2) = 31,415.92 Td
62
Using artificial light sources, which type of light is for longer wavelengths, and has a high performance? (It's a filament that's heated)
Incandescent
63
Using artificial light sources, which type of light has a behavior that is eradic for different wavelengths, showing spikes across the spectrum?
Fluorescent
64
Using artificial light sources, which type of light uses the blue spectral region?
LED
65
Theoretical construct that is convenient for describing sources of EMR, including light sources
Blackbody radiator
66
What does a blackbody radiator absorb and reflect?
- Absorbs all light/energy that's thrown at it
| - Reflects nothing
67
When talking about blackbody radiators and color temperature, as the temperature increases, what happens to the peak wavelength and the power (area under the spectral distribution curve)?
As temp inc, peak wavelength dec, and power inc
68
As you shift from 10,000K (kelvin) to 5,000K to 2,000K, when discussing blackbody radiators and color temp, what happens to the peak wavelength?
There's a shift in the peak as temperature changes
69
A blackbody radiator with a temperature of 2,000K has most of it's power concentrated at what wavelength?
Longer wavelengths
70
A blackbody radiator with a temperature of 10,000K has most of it's power concentrated at what wavelength?
Shorter wavelengths
71
For blackbody radiators, most energy is concentrated in the shorter wavelength as the temp is __1__ and concentrated in the longer wavelength as the temp is __2__.
1: Higher
2: Lower
72
Which color temperature would appear yellow-white because of it's relatively higher energy level in the long-wavelength region of the spectrum?
2,000K
73
Which color temperature would appear blue-white because of it's relatively higher energy level in the short-wavelength region of the spectrum?
10,000K
74
Between a 4000K LED and a 2700 high pressure sodium bulb, which one allows us to see better at night?
4000K LED
75
What's the disadvantage of being able to see with a 4,000K LED at night better than with a 2,700K bulb?
It has 3 times more scattering at 465nm than at 600nm (Rayleigh Scattering)
76
The higher the color temperature, what color is the light, how much scatter is there, and what's the area of glare?
- Bluer the light
- More the light scatters
- The larger the area of glare
77
What kind of glare does higher color temperature cause?
Discomfort glare
78
Who does discomfort glare affect most?
Presbyopes and cataract patients
79
RGB cones response is from what 2 wavelengths?
400-700nm
80
RGB cones peak response is at what wavelength?
555nm
81
Rods response is from what 2 wavelengths?
400-600nm
82
Rods peak sensitivity is at what wavelength?
507nm
83
The peak luminous efficacy of photopic vision (day vision, where only cones are active) is what?
680 lu/W
84
The peak luminous efficacy of photopic vision (day vision, where only cones are active) has a peak response of what wavelength?
555nm
85
The peak luminous efficacy of scotopic vision (night vision, where only rods are active) is what?
1700 lu/W
86
The peak luminous efficacy of scotopic vision (night vision, where only rods are active) has a peak response of what wavelength?
507nm
87
Photopic vision
Day vision
| Only cones active
88
Scotopic vision
Night vision
| Only rods are active
89
Mesopic vision
Sundown (light/dark)
| Both rods and cones are active
90
At mesopic and scotopic conditions, the eye is more sensitive to what wavelength of light, and what color temperature source?
Shorter wavelengths
| Higher color temperature sources
91
A filter that passes only a certain specified spectral band of light
Bandpass filter
92
What filter is not based on color, but only wants a specific wavelength (ex: only b/w 500 and 550 nm)?
Bandpass filter
93
A filter that passes only a narrow spectral band of light
Narrowband filter
94
A filter that passes only a broader spectral band of light
Broadband filter
95
A filter that transmits long wavelengths of light, but not shorter wavelengths
Long-pass filters
96
Filters that produce a very narrow band of light based on the interference principle of light
Interference filters
97
Color mixture with 1 long pass and 1 short pass filter, together in sequence
Subtractive color mixtures
98
Explain subtractive color mixtures
2 filter combination in sequence transmits less light than either one by itself
(Light source)--[lots of light = long wavelength]-->(filter #1)--[less light = shorter wavelength)-->(filter #2)--[even less light = shorter wavelength]
99
Color mixture with 2 different color filters, both projecting onto a screen
Additive color mixtures
100
Explain additive color mixtures
Light is projected through 2 different color filters and combined on a screen to produce an additive mixture. It has more light than either one by itself.
101
Filter that transmits all wavelengths equally and minimizes color distortion
Neutral density filter
102
Neutral density (ND) filters are specified by their what?
Optical density (OD)
103
How do you calculate the optical density for a neutral density filter?
OD = log(1/T)
OD is in log units
T is the fraction transmittance
104
Why are ND filter used in combination with high-pass filters?
Block UV radiation in sunglasses to minimize color distortion for patients who have anomalous (varying from the norm) color vision
105
Choosing an ND filter with a higher optical density will translate to ____ transmission and ____ absorption of the incident light.
Lower transmission
| Greater absorption
106
For higher transmission and less absorption, a ____ optical density would be appropriate.
Lower optical density
107
Where is UVB absorbed?
By the skin epidermis
108
What does UVB absorption result in?
Sunburn
109
Absorption of high-energy radiation (UVB), can damage and lead to what?
Damage DNA, leading to skin cancer
110
How does early exposed to UVB rays affect children and adults?
Exposure early in life appears to be particularly harmful, predisposing a child to developing skin cancer later as an adult.
111
When is UVB present in North America?
During the summer months
112
Where is UVA absorbed?
By the skin epidermis and underlying dermis
113
Absorption of high-energy radiation (UVA) promotes what?
Wrinkling of skin
114
When is UVA present in North America?
During all four seasons
115
What are some important structures that are vulnerable to UV radiation?
Ocular tissues, as well as the adnexa (the areas around the ocular tissues)
Skin
116
Acute exposure to UVC can cause what?
Painful solar keratitis
117
When is UVC present, and when can you get painful solar keratitis?
When snow skiing without ocular protection
118
Chronic UV exposure appears to play a role in the development of what?
Pinguecula, pterygium, and certain cataracts and may contribute to the development of age-related macular degeneration (AMD)
