Sensitivity of the Human Eye & Illumination

Question 1

What is Radiometry?

Answer 1

It is the measurement of light in any portion of the electromagnetic spectrum (UV, visible light and infrared light)

Number of photons, the triangleE of the individual photons or the radiant flux

Question 2

What is Photometry?

Answer 2

Measurement like in radiometry but describes taking the human visual system into account e.g. light/luminance intensity of the human eye

Question 3

How do we convert radiometric to photometric units?

Answer 3

Provided by luminous efficiency/eye sensitivity function

Question 4

What is luminous efficiency/eye sensitivity function?

Answer 4

How we convert radiometric to photometric units

Question 5

What does C equal?

Answer 5

3 x 10^8

Question 6

What does h equal?

Answer 6

6.63 x 10^-34

Question 7

What does e equal?

Answer 7

1.6 x 10^-19

Question 8

What are individual photons measured in?

Answer 8

Joules (J)

Question 9

How do we work out eV?

Answer 9

J/e

Question 10

What does triangleE equal?

Answer 10

Joules (J) or hf
(6.63 x 10^-34 x Frequency)

Question 11

What does J equal?

Answer 11

triangleE

Question 12

What does hf mean?

Answer 12

(6.63 x 10^-34) x Frequency

Question 13

What is Radiant Flux?

Answer 13

Measure of energy across a unit of time measured in Js-1 or Watts
Measures total electromagnetic radiation emitted by a source, including all wavelengths (visible, infrared, and ultraviolet)

Question 14

What is luminous intensity?

Answer 14

Photometry - measurement of light intensity

Question 15

What is luminous intensity measured in?

Answer 15

Candelas

Question 16

What is the radiant flux of a monochromatic light source?

Answer 16

1/683W at 555nm into a solid angle of 1 Steradian (sr) with a luminous intensity of 1cd

Question 17

What is a Radian?

Answer 17

Radiant “cuts out” length of a circle’s circumference equal to the radius

Question 18

What is a Steradian?

Answer 18

Steradian “cuts out” an area of sphere = r^2

Question 19

A smaller radius = smaller steradian. What happens to surface area: radius?

Answer 19

Ratio surface area to radius is constant

Question 20

What’s the difference between radiant flux and luminous flux?

Answer 20

Radiant flux measures the total electromagnetic radiation emitted by a source, including all wavelengths (visible, infrared, and ultraviolet), while luminous flux measures the perceived power of visible light, considering the human eye’s sensitivity to different wavelengths.

Question 21

What do we need to know to convert radiometric to photometric units?

Answer 21

Wavelength aka knowledge of the light source

Question 22

What is Luminous Flux?

Answer 22

Light power flowing from source as perceived by the eye (visible light)

Question 23

What is Luminous Flux measured in?

Answer 23

Lumens (lm)

Question 24

What is 1 candela equal to?

Answer 24

1 lm sr-1

Question 25

What is Illuminance?

Answer 25

Luminous flux per unit area measured in lux (lm m^-2) Cares only for light reflected by the surface

Question 26

What should light be considered?

Answer 26

A sphere

Question 27

What is the surface area of a sphere?

Answer 27

4πr^2

Question 28

Why is the relationship between strength of source (S) and distance to object of regard important?

Answer 28

If we halve the distance between source and object illuminance increases by 4x and if halves again increases by 16x = Important for LVAs

Question 29

What is the relationship between luminous intensity and illuminance?

Answer 29

Inverse Square

Question 30

What is luminance?

Answer 30

(Luminous Intensity) Amount of luminance in any given direction of a surface emitting light in one direction / area of surface perpendicular to the direction

Question 31

What is luminous intensity measured in?

Answer 31

Candelas per unit area of a surface (nit, nt)

Question 32

What is a Candela?

Answer 32

Luminous Intensity

Question 33

When is photopic luminous efficiency most effective?

Answer 33

At 555nm

Question 34

What is the 'Purkinje' shift?

Answer 34

Shift from photopic to scotopic

Question 35

When is scotopic luminous efficiency most effective?

Answer 35

At 505nm (shift away from red wavelengths makes them harder to see)

Question 36

What is the Stiles-Crawford Effect?

Answer 36

That cones have directional sensitivity and thus have a built in mechanism to deal with aberrations (provide a lesser response to oblique rays)

Question 37

How do we get the visible spectrum?

Answer 37

Tissues only absorb light if their structure allows; light not absorbed by other ocular structures are absorbed by the photoreceptors.

Question 38

What wavelengths does the cornea absorb?

Answer 38

< 295nm

Question 39

What wavelength does the lens absorb?

Answer 39

300 - 400nm (the majority of UV rays that the cornea doesn't)

Question 40

What happens as the lens becomes more cataractous?

Answer 40

More cataractous = absorbs more short wavelengths

Question 41

What wavelength does the vitreous absorb?

Answer 41

Similar to water absorbing infra-red wavelengths of > 1,400nm

Question 42

What waves reach the retina?

Answer 42

400 - 1,400nm

Question 43

What is LASER dependent on?

Answer 43

Dependent on tissue absorption so the wavelength needs to pass through

Question 44

What wavelengths are used in LASER?

Answer 44

- Argon (515nm) - Krypton (614nm)

Question 45

What wavelength do we use in corneal curvature correction?

Answer 45

Ultraviolet (193nm, Argon Flouride)

Question 46

What does the transduction of light by photoreceptors produce?

Answer 46

It's an energy demanding process and creates harmful byproducts called reactive oxygen species and free radicals

Question 47

What are reactive oxygen species and free radicals?

Answer 47

Harmful byproducts after photoreceptor transduction Oxygen compounds with missing ions or electrons and are highly reactive leading to necrosis of retinal cells

Question 48

What can product us against reactive oxygen species and free radicals?

Answer 48

Macular pigments protect as they're anti-oxidents. We can get this from our diets; Lutein and Zeaxanthin (transformed into meso-zeaxanthin)

Question 49

Where do we get macular pigments from?

Answer 49

We can get this from our diets; Lutein and Zeaxanthin (transformed into meso-zeaxanthin)

Question 50

What did Ma et al (2012) find about macular pigments?

Answer 50

Less severe AMD in those with Lutein and Zeaxanthin (transformed into meso-zeaxanthin) supplements Reduced smoking is also helpful

Question 51

What is the fundamental unit of Radiometry?

Answer 51

Radiant Flux

Question 52

What is Luminous Intensity?

Answer 52

Luminous intensity, on the other hand, is a specific photometric quantity that measures the light emitted by a source in a particular direction per unit solid angle How we measure photometry

Question 53

What's the difference between luminance intensity and luminous flux?

Answer 53

Luminance intensity measures the brightness of light emitted in a specific direction, while luminous flux represents the total amount of light emitted by a source in all directions. Luminance Intensity = Candelas Luminous Flux = Lumens (weights to match eye response of a standard observer)

Question 54

The intensity at the surface of the sphere is given by:

Answer 54

S/4πr2

Question 55

What is luminance?

Answer 55

Luminance is the luminous intensity per unit area of light