Radiometry/ Photometry

Question 1

visual acuity testing is specified to have a minimum chart luminance of ______

Answer 1

85 cd/m^2

Question 2

what is radiometry?

Answer 2

the science of the measurement of electromagnetic radiation

Question 3

what is photometry?

Answer 3

the science of the measurement of the eye’s response to (or perception of) electromagnetic radiation

Question 4

what is the total power output of a light source measured in watts (joules/second)

Answer 4

radiant flux (aka radiant power)

Question 5

units of radiant flux (radiant power)

Answer 5

Watts (Joules/Second)

Question 6

what is the power output of a point (light) source in a given direction (solid angle), measured in watts/steradian

Answer 6

Radiant Intensity

Question 7

units of radiant intensity

Answer 7

watts/steradian

Question 8

a sphere contains how many steradians

Answer 8

4 pi steradians

Question 9

what is the radiant intensity per unit projected area of an extended source, measured in watts/ square meter steradian

Answer 9

radiance

Question 10

units of radiance

Answer 10

watts / square meter steradian

Question 11

what is the radiant flux incident on an object’s surface, measured in watts/ square meter

Answer 11

irradiance

Question 12

units of irradiance

Answer 12

watts/ square meter

Question 13

what is the energy received per unit area of irradiated surface, measured in J/m^2

Answer 13

radiant exposure

Question 14

UV exposure limit

Answer 14

0.003 J/cm^2

in a day for cornea/skin

Question 15

visible light exposure limit

Answer 15

3 J/cm^2

Question 16

IR exposure limit

Answer 16

3000 J/cm^2

Question 17

what is the total power output of a light source, measured in lumens

Answer 17

luminous flux (luminous power)

Question 18

a ____ nm light is the ‘brightest’

Answer 18

555 nm

Question 19

peak for scotopic conditions is _____ nm

Answer 19

507 nm

Question 20

why is 555 nm light the ‘brightest’?

Answer 20

it has the most ‘luminosity’ or highest luminous efficiency for photopic conditions

Question 21

there are ___ lumens per watt at 555nm

Answer 21

683 lumens/watt

Question 22

for scotopic functions, ____ lumens/watt at 507nm

Answer 22

1700 lumens/watt

Question 23

what is the power output of a point light source in a given direction (solid angle), measured in lumens/steradian

Answer 23

luminous intensity

Question 24

units of luminous intensity

Answer 24

lumens/ steradian

candela, cd

Question 25

what is the luminous intensity per unit projected area of an extended source, measured in candelas/ square meter

Answer 25

luminance

Question 26

units of luminance

Answer 26

• candelas/ square meter
• nit
• foot-lambert (fL)

Question 27

10^-6 to 10^-1 cd/m^2 is for ______ vision

Answer 27

scotopic

Question 28

10^-1 to 10^1 cd/m^2 is for _______ vision

Answer 28

mesopic

Question 29

10^1 to 10^7 cd/m^2 is for _______ vision

Answer 29

photopic

Question 30

the eye operates over a tremendous range of light levels, about ___ log units

Answer 30

12 log units

Question 31

what is luminous flux incident on an object’s surface, measured in lumens/square meter (lux)

Answer 31

illuminance

Question 32

units of illuminance

Answer 32

• lumens/ square meter
• lux
• lumens/ square foot (ft-cd)

Question 33

1 fL = ___ cd/m^2

Answer 33

3.43

Question 34

1 fc = _____ lux

Answer 34

10.76

Question 35

_____ is defined (arbitrarily) as an amount of light getting into the eye

Answer 35

retinal illuminance

Question 36

units of retinal illuminance

Answer 36

trolands (td)

Question 37

formula for retinal illuminance calculations

Answer 37

trolands = luminance (cd/m^2) x pupil area (mm^2)

Question 38

what is a special kind of surface whose luminance does not vary with the angle at which it is viewed

Answer 38

• lambertian diffuser

- cosine diffuser, perfect diffuser

Question 39

how does luminous intensity change with distance?

Answer 39

it does not change with distance

Question 40

how does luminance change with distance?

Answer 40

luminance does not change with distance

Question 41

how does luminance of an extended source change with viewing distance?

Answer 41

it doesn’t

brightness constancy

Question 42

how does luminance of an extended source change with viewing distance? (for the same angular subtense of view)

Answer 42

the viewed area (projected area) of the stimulus decreases (linear dimensions) at sorted distances