Session 13

Question 1

Light from a smooth, non diffusing surface has been polarized in the reflection process.
What are some of these surfaces?4

Answer 1

Water
Snow
Highways
Metallic Surfaces

Question 2

When are polarized lenses not ideal?4

Answer 2

Pilots
People who use a digital display (LCD screen)
Some car windscreens
Golfers/skiers find it hard to judge surfaces

Question 3

What visual affect do the 3 colors give in a polarized lens?

Answer 3

Grey - Neutral/lowers intensity equally
Brown- Changes the colors/good contrast
Green - Makes green brighter

Question 4

What do polarizing lenses do?

Answer 4

They block the light polarized in one plane, thus cutting the glare the eye experiences.

Question 5

How are polarized lenses made? and what direction should you put the lenses in?

Answer 5

The polarizing filter is between the two lens surfaces.
Must be orientated along the 180 meridian, if you turn the blank it wont be in the right orientation to cut the glare out.

Question 6

When should a polarized lens be worn? 6

Answer 6

-General sunglass
-To decrease driving fatigue
-For fishing/boating
-For more visual comfort at the beach (water/sand)
-Snowy days - not as blinding
-To block UV radiation

Question 7

What is a scratch resistant coating?

Answer 7

Develop more surface hardness/ resistant to scratching

Question 7

What are the 2 main purposes of anti reflective coating?

Answer 7

Reduce unwanted reflections
Increases light transmission

Question 7

What two methods are used to apply SRC?

Answer 7

UV cured - coating spun on then UV cured
Thermally cured - Dipped and removed carefully, then thermally cured

Question 8

How does the refractive index impact light transmission?

Answer 8

The higher the refractive index the less light is let through so more reflections and worse visual comfort. AR is included as standard

Question 9

How much light is transmitted in a CR39 vs 1.74?

Answer 9

CR39 - 92.2%
1.74 - 85.9%

Question 10

Look at Figure 22.11 pg - 445/ Powerpoint session 13

Question 11

How are multilayer AR coatings made/designed?

Answer 11

Each layer address a section of the Visible spectrum normally sealed with a hydrophobic outer layer and adhered to a SRC (inner layer).

Question 12

What is the relationship between an ARC and SRC?

Answer 12

AR coating adheres to the lens better if their is a SRC.
AR are hard and brittle + plastic lenses are soft and spongy.
The SRC supports the AR coating.

Question 13

Does AR affect a tinted lens?

Answer 13

Yes, it makes it appear lighter and may change the color or hue. It is unpredictable.

Question 14

What are the pros of AR? 9

Answer 14

-Better light transmission
-Decreased glare
-Better night driving (headlights, lamps etc)
-Good for photos
-Eyes visible
-Hydrophobic
-Can make thick lenses look thinner
-Antistatic
-Easier to clean

Question 14

Review Caring for AR + Correct ways to clean p449 S.O.D

Question 15

What are the cons for AR? 2

Answer 15

-Expensive
-Damaged if not cared for properly ( Construction workers should not have them.

Question 16

How are Mirror coating applied?

Answer 16

Vacuum process to the front surface so it has the same properties as a two way mirror.
Wearer=see out
Observer=cant see in

Question 17

Can mirror tints be combined with anything else?

Answer 17

Yes they are often combined with tints and polarizing filter to help with sunlight glare.

Question 18

Do Mirror lenses scratch easily?

Answer 18

Yes.

Question 19

What is an edge coating? 2
How is it applied?

Answer 19

A coating applied to the edge of a lens (by the bevel) to reduce the look of thicker lenses.
Matches the color of the frame, painted on then hardened in an oven.

Question 20

What order should a AR and SRC be applied?

Answer 20

SRC first then AR after. AR is normally the final coating

Question 21

What is Discomfort Glare?

Answer 21

Produces discomfort but does not necessarily reduce visual resolution.

Question 22

When can someone experience discomfort glare?

Answer 22

When looking from high and low light intensities in a small viewing area.
-TV in dark room.
-Computer in front of bright window.

Question 23

What is disability glare?

Answer 23

Glare that reduces the visual performance and visibility and may be accompanied by discomfort

Question 24

When can disability glare occur? 2

Answer 24

Car headlights oncoming in a dark road makes it impossible to see someone in dark clothing at the side of the road.
Cataracts

Question 25

What happens when you add multiple layers of a specifically determined refractive index on the lens?

Answer 25

More light is allowed to pass through when more layers are added.
If coated correctly a large percentage of the reflected light is now allowed to pass through the lens.