Photometry and Radiometry

Question 1

A source produces 20W at 650nm. Assuming a luminous efficiency of 0.10, how many lumens are produced?

a. 0.146 lumens
b. 68.5 lumens
c. 650 lumens
d. 1360 lumens
e. 1650 lumens

Answer 1

1360 lumens

Question 2

An illuminance probe is used to measure the illuminance EL in a classroom. The reading obtained is 70 foot-candles. The probe measures 3x3 cm. How many lumens are incident on the surface of the probe?

a. 0.45 lumens
b. 0.56 lumens
c. 0.68 lumens
d. 0.73 lumens
e. 0.87 lumens

Answer 2

0.68 lumens

Question 3

A point source has a luminous intensity IL of 100 cd. What illuminance EL does it produce at a distance of 2ft?

a. 269 lux
b. 329 lux
c. 379 lux
d. 399 lux
e. 429 lux

Answer 3

269 lux

Question 4

. A point source of 50cd is 1ft from a sheet of paper. Another point source at 3 ft from the same piece of paper illuminates the paper equal to the first source. What is the intensity of this unknown point source?

a. 150 cd
b. 300 cd
c. 400 cd
d. 450 cd
e. 500 cd

Answer 4

d. 450 cd

Question 5

An illuminance meter is tilted 60 degrees from the perpendicular position with respect to a point source of light. The meter reads 100 lux and is 2 ft from the source. What is the intensity of the point source?

a. 74cd
b. 80 cd
c. 96 cd
d. 125 cd
e. 400 cd

Answer 5

a. 74cd

Question 6

A matte (Lambertian) surface with a reflectance of 0.7 has a luminance of 50 foot-Lamberts. What is the illuminance falling on the surface?

a. 71.4 foot-candle
b. 154.3 foot-candle
c. 255.2 foot-candle
d. 380.1 foot-candle
e. 770.6 foot-candle

Answer 6

a. 71.4 foot-candle

Question 7

By use of the inverse square law and an illuminance device, the intensity of a point source is determined to be 25 cd. Assume this uniform point source produces the same amount of light in all directions. How many total lumens does it produce?

a. 274 lumens
b. 314 lumens
c. 365 lumens
d. 398 lumens
e. 424 lumens

Answer 7

b. 314 lumens

Question 8

A light source is located 3 ft from a matte surface. The illumination falling onto the surface is 100 lux. The luminance of this surface, at an angle of 30 degrees, is 5 foot-Lamberts. What is the reflectance of this surface?

a. 46%
b. 54%
c. 77%
d. 83%
e. 105%

Answer 8

b. 54%

Question 9

8a. A light source is located 3 ft from a NON-Lambertian surface. The illumination falling onto the surface is 100 lux. The luminance of this surface, at an angle of 30 degrees, is 5 foot-Lamberts. What is the reflectance of this surface?
a. 46%
b. 62%
c. 77%
d. 83%
e. 105%

Answer 9

b. 62%

Question 10

What is the sensitivity of a patient who can just detect a target luminance of 500 apostilbs at a maximum stimulus luminance of 10,000 apostilbs?

a. 12 dB
b. 13 dB
c. 15 dB
d. 20 dB
e. 30 dB

Answer 10

13 dB