Session 13 Flashcards
(28 cards)
Light from a smooth, non diffusing surface has been polarized in the reflection process.
What are some of these surfaces?4
Water
Snow
Highways
Metallic Surfaces
When are polarized lenses not ideal?4
Pilots
People who use a digital display (LCD screen)
Some car windscreens
Golfers/skiers find it hard to judge surfaces
What visual affect do the 3 colors give in a polarized lens?
Grey - Neutral/lowers intensity equally
Brown- Changes the colors/good contrast
Green - Makes green brighter
What do polarizing lenses do?
They block the light polarized in one plane, thus cutting the glare the eye experiences.
How are polarized lenses made? and what direction should you put the lenses in?
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.
When should a polarized lens be worn? 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
What is a scratch resistant coating?
Develop more surface hardness/ resistant to scratching
What are the 2 main purposes of anti reflective coating?
Reduce unwanted reflections
Increases light transmission
What two methods are used to apply SRC?
UV cured - coating spun on then UV cured
Thermally cured - Dipped and removed carefully, then thermally cured
How does the refractive index impact light transmission?
The higher the refractive index the less light is let through so more reflections and worse visual comfort. AR is included as standard
How much light is transmitted in a CR39 vs 1.74?
CR39 - 92.2%
1.74 - 85.9%
Look at Figure 22.11 pg - 445/ Powerpoint session 13
How are multilayer AR coatings made/designed?
Each layer address a section of the Visible spectrum normally sealed with a hydrophobic outer layer and adhered to a SRC (inner layer).
What is the relationship between an ARC and SRC?
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.
Does AR affect a tinted lens?
Yes, it makes it appear lighter and may change the color or hue. It is unpredictable.
What are the pros of AR? 9
-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
Review Caring for AR + Correct ways to clean p449 S.O.D
What are the cons for AR? 2
-Expensive
-Damaged if not cared for properly ( Construction workers should not have them.
How are Mirror coating applied?
Vacuum process to the front surface so it has the same properties as a two way mirror.
Wearer=see out
Observer=cant see in
Can mirror tints be combined with anything else?
Yes they are often combined with tints and polarizing filter to help with sunlight glare.
Do Mirror lenses scratch easily?
Yes.
What is an edge coating? 2
How is it applied?
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.
What order should a AR and SRC be applied?
SRC first then AR after. AR is normally the final coating
What is Discomfort Glare?
Produces discomfort but does not necessarily reduce visual resolution.
