Antireflective Lenses Flashcards
For A/R coating to reduce reflections, an A/R coating must meet 2 conditions:
1) path condition - determines what the optical thickness of a single layer coating film must be
2) amplitude condition - amplitude of light waves in the lens material and the film must be equal
path condition:
film must be _ of wavelength thick or _ multiples of that
1/4, odd
path condition:
when light strikes the single layer coated lens surface, some light will reflect from _ and some from _
this causes _ phase, _ interference, and prevents reflections
coating surface
lens surface
out of, destructive
amplitude condition:
requires the amplitude of the light waves in the lens material and film to be _, creating _ interference
equal, destructive
amplitude condition:
index of film must be equal to _ of index of material being coated
square root
single layer coatings are not 100% effective because:
correct coating thickness for yellow waves is not correct for red or blue (blue and red are reflected more and form purple cast)
multilayer coatings (8 layers) work by:
adding more layers of coating, each specific to wavelength and increasing amount of light transmitted that would have normally been reflected
multilayer coatings are not placed directly on lens;
first _
then _
then _
primer
hardcoat
adhesion
when alternating layers of low and high index materials, it is possible to obtain reflectivity as low as _%
0.1
_ is primary material used for AR coatings as in Silica
Magnesium Fluoride (n=1.38)
AR is sealed with either _ or _ coating
hydrophobic or oleophobic
many new coatings are so efficient in repelling smudges, a temporary _ is applied to prevent slippage during edging
gripper coat
multilayer AR coatings are very important for _ lenses as they naturally transmit less light
high index
AR coatings are hard and brittle
plastic lenses are soft and spongy
-what supports brittle AR coating?
hardcoat
designing AR for the material that it will be placed upon is known as _
substrate matching
color that you can see on the lens is called
reflex color
multilayer coatings do not have purple cast; most today have _ appearance
blue-green
if lens has a reflex color that changes from one section of lens to another, it is an indication of _
even coating thickness
reflex color can be any color and still be effective; it also can have virtually _ and still be effective
no color
applying an AR coating _ a tinted lens;
therefore required to tint a lens _% darker than desired if AR is going to be applied
lightens
10-15
AR coating has what effect on sunglasses?
reduced mirror like reflections from back surface
pros of AR:
less reflections eyes more visible improved contrast less halos with night driving easier to clean/stays cleaner
cons of AR:
cost
smudges are more visible
AR coatings are _ fragile
thermally, chemically
HEV (blue light) _ more easily than other visible light
scatters (not easily focused)
blue light is perceived as _ and contributes to _
noise; digital eye strain
excessive blue light can damage light sensitive cells in the retina, like _
Macular Degeneration
_ is altered by blue light exposure
Circadian Rhythms
some blue light is essential for health, benefits?
alertness, memory, cognitive function, elevates mood
lack of blue light in fall and winter?
Seasonal Affective Disorder
Coating including blue light blocking
Lens that blocks blue light
Prevencia
Blue Tech
Lenses that filter HEV light had undesirable yellow cast, now in clear
_ is best option
blue filtering AR coatings
product that you should prescribe to all patients that are heavy users of devices
Blue light, AR filters
4 major manufacturers of coating equipment
essilor
hoya
satis
zeiss/sola
