Absorptive Lenses

Question 1

UVA wavelength

Answer 1

320-380 nm

Question 2

UVB wavelength

Answer 2

290-320 nm

Question 3

UVC wavelength

Answer 3

200-290nm

Question 4

Visible spectrum wavelength

Answer 4

380-760nm

Question 5

Infrared spectrum

Answer 5

760nm - 1mm

Question 6

What 3 factors determine light transmission through a lens?

Answer 6

1)percentage of light lost by reflection-front surface
2)percentage of light lost by absorption
3)percentage of light lost by reflection-back surface

Question 7

What is the equation to find the amount of light reflected by a lens surface? (Reflection Equation)

Answer 7

Amount of light reflected = (n’ - n)^2 (I) / (n’+n)^2

Question 8

What is the equation to find the amount of light that is transmitted through a lens?

Answer 8

Transmission= Incident Light - Absorption - Reflection

Question 9

What does Lambert’s law of absorption say? What factor represents this?

Answer 9

For an absorptive material, layers of equal thickness absorb equal quantities (percentages) of light regardless of the intensity of the light.

Transmittance factor (q)

Question 10

How do you find Transmission when incident light and transmittance factor is given?

Answer 10

Transmission= incident light (%) x transmittance factor (q) (number of thicknesses)

Question 11

How do you find ultimate transmission?

Answer 11

individual transmissions multiplied by the others if it passes through more than one lens.

Question 12

What is opacity? Equation?

Answer 12

Reciprocal of transmission

Opacity= 1/Transmission

Question 13

How do you find ultimate opacity?

Answer 13

Opacity multiplied by other opacities.

Question 14

How do you find optical density?

Answer 14

Optical density= -log(transmission)

Question 15

How much transmission is normal for plastic sunglass lenses?

Answer 15

15-30%

Question 16

How much transmission is normal for general-purpose lenses?

Answer 16

8%-40%

Question 17

What do photochromic glass lenses contain that allows them to change color?

Answer 17

silver halide crystals.
Turns into silver and halogen atoms with UV.

Question 18

What do corning photochromic filter (CPF) lenses look like? What are they used for?

Answer 18

Appear orangish.
They filter out the shorter wavelengths like blue in order to relieve glare for patients with severe light sensitivity.

Question 19

What molecule is found in plastic transition lenses that allow them to change color?

Answer 19

Spiro-Oxazine molecule

Question 20

What is meant by an imbibed photochromic lens (transition lens)?

Answer 20

The lens darkens evenly across the lens regardless of prescription. The transition layer is on the outside surface of the lens only.

Question 21

What is meant by an In-mass photochromic lens (transition lens)?

Answer 21

The transition molecules are found throughout the whole lens. They darken up to 50% in the car. Scratches do not affect performance. The transition molecules never wear out.

Question 22

What transition lenses do not change behind a car windshield?

Answer 22

Transition Signature Lenses GEN 8

Question 23

What transition lenses DO change and have moderate activation behind a car windshield?

Answer 23

Transition XTRActive Lenses New Generation
Transition Drivewear Lenses

Question 24

What is a concern with transition motorcycle visors?

Answer 24

Whether or not they can change quick enough if they were to go under a tunnel.

Question 25

What are the 4 types of glare?

Answer 25

Distracting Glare Discomfort Glare Disability Glare Reflected Glare

Question 26

What type of glare is caused by lens reflections?

Answer 26

Distracting glare

Question 27

What type of glare is caused by stray light that causes visual discomfort but does not interfere with resolution?

Answer 27

Discomfort glare

Question 28

What kind of glare makes objects appear like they have lower contrast than they would without the glare. It increases the brightness of the background and lowers the brightness of the nearby object?

Answer 28

Disability glare

Question 29

What kind of glare is caused by reflected light sources and known as 'blinding glare"?

Answer 29

Reflected glare

Question 30

Axis that blocks all polarized light incident at that axis

Answer 30

Absorption axis

Question 31

Axis that transmits all polarized light incident at that axis

Answer 31

Transmission axis

Question 32

What direction of light is mostly reflected off a horizontal surface like a body of water?

Answer 32

Horizontal light waves

Question 33

What materials polarize light the best?

Answer 33

Nonconducters, dielectrics, glass, pavement, sand, snow

Question 34

The angle where all the light reflected off a dielectric is completely polarized

Answer 34

Brewster/s Angle

Question 35

How do you find Brewster's Angle?

Answer 35

Tan(i) = n' i= angle of incidence n'= index of the medium

Question 36

How to solve for i in brewster's angle equation

Answer 36

i= tan^-1 (n')

Question 37

What does malus's law determine? What is the equation?

Answer 37

Determines the intensity of light that passes through two perfect polarizers. Io = I cos2 θ I= initial intensity Io= intensity after two polarizers θ= angle betweeen transmission axis of the polarizers

Question 38

What percent of transmission must aviation glasses have?

Answer 38

At least 15% of transmission