Radiometry/Photometry

Question 1

What are the wavelength ranges for UVA , UVB, UVC? What absorbs each? What is a result of absorption of UVA and UVB?

Answer 1

UVA: 320-400 nm. Absorbed by lens

UVB: 280-320 nm. Absorbed by lens

UVC: 200-280 nm. Absorbed by ozone layer and cornea.

Absorption of UVA and UVB leads to progression of cortical cataracts.

Question 2

Wavelengths for near, mid, and far Infrared radiation

Answer 2

Near: 800-2500 nm

Mid: 2500- 50,000 nm

Far: 50,000 - 10^6 nm

Question 3

What size of wavelengths are more dangerous? Shorter wavelengths or longer? Why?

Answer 3

Shorter wavelengths (higher frequency) are more dangerous due to their higher energy.

Question 4

If a wave has a higher amplitude, it will be _______ than a wave that has a lower amplitude.

Answer 4

Brighter

Question 5

Wavelength and frequency are ___________ proportional.

Answer 5

Inversely proportional

Question 6

Formula for frequency of light

Answer 6

v = c / λ

v = frequency of light
c = speed of light (3 x 10   m/s)
λ= wavelength of light

Question 7

As the wavelength gets longer, the frequency gets _______.

Answer 7

Smaller

Question 8

Energy equation

Answer 8

E = hv

E  =  energy per photon
h  =  Planck’s constant (6.626 x 10   J -sec)
v  =  frequency

OR

E = hc / λ

E  =  energy per photon
h  =  Planck’s constant (6.626 x 10    J -sec)
c  =  speed of light (3 x 10   m/s)
λ  =  wavelength

Question 9

As the wavelength gets longer, the energy per photon is ______.

Answer 9

lower

Question 10

A type of retinal ganglion cell (ipRGC) contains a photopigment called _________. What does it do when it is stimulated?

Answer 10

Melanopsin. When stimulated by sunlight, the cell sends information to the suprachiasmatic nucleus (hypothalamus), which is involved in setting the body’s circadian rhythms.

Question 11

What is the bandwidth of blue light?

Answer 11

446-477 nm

Question 12

What does radiometry have to do with?

Answer 12

Has to do with measurements of electromagnetic radiation, regardless of the eye’s ability to detect it. (Watts)

Question 13

What does spectrometry have to do with?

Answer 13

Has to do with measurements of 
electromagnetic radiation that has an effect on the visual system. (Lumens)

Question 14

Definition of luminous power and its units.

Answer 14

Total light power produced by a source.

Common units: Lumens in joules per second OR watts

Radiometric equivalent: radiant power

Question 15

Luminous intensity definition and units

Answer 15

Light power produced in a solid angle produced by a point source.

Units: Lumens/steradian or candelas

Radiometric equivalent: radiant intensity in watts/steradian.

Question 16

Luminance definition and units

Answer 16

Luminous intensity per unit projected area of an extended source.

Units: candelas/ m^2 or foot lamberts

Radiometric equivalent: radiance in watts/steradian/square meter

Question 17

Illuminance definition and units

Answer 17

Luminous power falling on a surface.

Units: Lumens/m^2 or lumens/ft^2\

Radiometric equivalent: Irradiance in watts/ m^2

Question 18

A _____ is a unit of radiant power. Its units are measured in ___________.

Answer 18

Watt; joule/second.

It can be a direct measure of output.

Question 19

A _____ is a unit for luminous power (light output)
or a small (“point”) source.

Answer 19

Lumen

Question 20

Abney’s Law of Additivity

Answer 20

Abney’s Law states that the TOTAL LUMINANCE of a light comprised of a MIXTURE of wavelengths is equal to the SUM of the luminances of all wavelengths in the mixture.

“Lumens are additive”

Question 21

Incandescent vs Luminescent lightbulbs

Answer 21

Incandescent lightbulbs: generate light through heat. Voltage differential causes filament to get hot, producing heat and light.

Luminescent lightbulbs: generate light through excitation of argon gas. The gas releases UV rays which are absorbed by a phosphor lining which re-emits light in the visible range.

Question 22

On a black body radiator, what are the x and y xis of spectral distribution of radiation graph.

Answer 22

X: Wavelength (nm)
Y: Spectral emittance (percent of emission)

Question 23

What relative emission (in K) is recommended for color testing?

Answer 23

6770 K

Question 24

For brightness matching test, when the two colors appear the same brightness, what is the person adjusting? Why is brightness matching difficult?

Answer 24

The person is adjusting the radiance or luminance to match the brightness of the fixed color. It is difficult for patient because of the color differences between the two stimuli.

Question 25

How do you find luminous efficiency?

Answer 25

of lumens = watts x 680 lumens/watt (photopic) x luminous efficiency

Solve for luminous efficiency

Luminous efficiency = # of lumens / watts x 680 lumens/watt (photopic)

Question 26

What is luminous efficiency?

Answer 26

the ratio of the total LUMINOUS power to the total RADIANT power of a source.

Question 27

Under scotopic conditions, what is the most sensitive wavelength and what is its lumens per watt

Answer 27

507 nm; 1700 lumens

Question 28

Describe luminous efficacy graph

Answer 28

It shows the absolute sensitivity of the visual
system to electro-
magnetic radiation is 
 different under photopic
vs. scotopic conditions. For anything under 555, the eye is more sensitive to it under photopic conditions.