Visual Science: Photometry 2: Chapter 4

Question 1

Scotopic Photometric Power

1. How many Lumens per Watt at 555 nm?
   a. What’s the ratio?

Answer 1

1. 680 Scotopic lumens per watt

2. Luminous efficiency of 555nm/(680 scotopic lumens per W) = Luminous efficiency of 507 nm/(X scotopic lumens/W)

Question 2

Heterochromatic Flicker Photometry (HFP)

1. What does a person do in this test?
   a. What does minimized flicker mean?
   b. What does it yield?
2. What’s the rate of Flicker?
   a. What does this produce?

Answer 2

1. Adjust radiance of the Sample stimulus so that Flicker is MINIMIZED
   a. That standard and sample wavelengths are at EQUAL LUMINANCE
   b. A Photopic Luminosity Function
2. 15 cycles per second
   a. Color Fusion, so only one color is seen

Question 3

Heterochromatic Flicker Photometry (HFP)

Minimally Distinct Border

1. The Results of HFP and MDB follow what Law?
2. The Standard wavelength and the Sample Wavelength are placed how?
3. What does the observer have to do?
4. At this end point, why does the border still exist?
   a. What has been eliminated?

Answer 3

1. Abney’s Law of Additivity
2. are Placed SIDE by SIDE w/a Border in between.
3. Adjust the RADIANCE of the SAMPLE so that the visibility of the BORDER is MINIMIZED
4. Only due to CHROMATIC CONTRAST
   a. LUMINANCE CONTRAST

Question 4

Light Source

1. How does an INCANDESCENT source generate light?
2. And a Luminescent?

Answer 4

1. Through HEAT

2. Through Excitation of INDIVIDUAL ATOMS

Question 5

Light source

1. Looking at the Spectral distribution of typical incandescent and fluorescent light sources, what does the INCANDESCENT source show?
2. What about the FLUORESCENT SOURCE?

Answer 5

1. a Relative Concentration of Energy at Long Wavelengths

2. Does NOT show a SKEWING power toward the long wavelength region of the spectrum, but it shows spikings.

Question 6

Black-Body Radiators

1. The Spectral Output of a Black-Body Radiator, is determined by what?
2. Wein’s Displacement Law
3. Stefan-Boltzman Law
4. What does this say about Peak Wavelength and Power as Temperature increases?

Answer 6

1. its Temperature
2. Peak Wavelength: alpha 1/T
3. Total Power alpha T^4
4. Peak Wavelength Decreases

and

Power Increases

Question 7

Black-Body Radiators

1. The Color Temperature of a light source is what?
   a. This radiates light of comparable hue to what?
2. Color Temperatures over 5,000K are called what?
3. Lower color temperatures (2,700-3,000K) are called what?

Answer 7

1. The temperature of an IDEAL Black Body Radiator
   a. to that of the Light Source
2. Cool Temperatures (blueish white)
3. Warm Colors (Yellowish white through Red)

Question 8

Black-Body Radiation

1. A Black body radiator with a Temperature of 2000K has MOST of its POWER CONCENTRATED at what?
2. but with a Temperature of 10,000K has its Power Concentrated at what?

Answer 8

1. Longer Wavelengths

2. Shorter Wavelengths

Question 9

Commercially available light sources are frequently specified by what?

2. 2000K source will appear what color?
   a. Why?
3. 10,000K source will appear what?
   a. Why?

Answer 9

1. by their COLOR TEMPERATURE: Incandescent Light Sources
2. Yellow-White
   a. Because it has Relatively More energy in the LONG-Wavelength Region of the Spectrum
3. Blue-White
   a. There’s Relatively more energy in the Short-Wavelength Region

Question 10

1. Nonincandescent sources, like Fluorescent bulbs are what kind of temperature?
2. What does this depend upon in a Fluorescent light tube?
3. How do they primarily emit light?

Answer 10

1. Correlated Color Temperature
2. On the Nature of the Phosphor that Coats the bulb
3. by Processes other than Thermal Radiation

Question 11

Colored Filters

1. A Color filter can do 1 of 2 things?
2. So how does this filter produce color?

Answer 11

1. May Absorb and/or Reflect some wavelengths that are INCIDENT upon it, while transmitting others.
2. The Filter subtracts light to produce color

Question 12

Narrowband Filter

1. What is it?
2. Filters of this type are typically specified by what 2 things?
3. The Half-height bandwidth is the spectral range over which the filter transmits what?

Answer 12

1. A Filter that PASSES only a NARROW SPECTRAL Band of light.
2. By the LOCATION of their Peak and their Half-Height Bandwidth
3. 50% or more of its peak transmission percentage.

Question 13

Broadband Filters

1. Have what kind of nature?
2. However, what is greater for a Broadband filter?
3. Long-Pass Filters Transmit what?
4. What do Interference Filters take Advantage of?
   a. What are they?

Answer 13

1. a Band-Pass Nature
2. The WIDTH of the BAND
3. Transmit LONG WAVELENGTHS but not short wavelengths
4. of the Interference of Light Waves to Produce a VERY NARROW BAND of LIGHT
   a. MONOCHROMATIC

Question 14

Subtractive and Additive Color Mixtures

1. What do color filters do?
2. The Additive Mixture contains MORE light than what?

Answer 14

1. They Subtract Light

2. Than that Emitted by either of the FILTERS.

Question 15

1. A Neutral Density Filter Transmits Wavelengths how?
   a. What does this do?

b. What are they specified by?

Answer 15

1. Transmits ALL WAVELENGTHS EQUALLY
   a. It MINIMIZES DISTORTION

b. Their OPTICAL DENSITY (OD)

OD = log (1/T)

T = fraction Transmittance of the Filter and OD is in Log Units