L10 Tints Flashcards

1
Q

Why do we dispense this?

A
  • to provide protection from uv light
  • to provide protection from glare (disability and discomfort)
  • to provide visual comfort
  • therapeutic and medical - certain condition eg cataract cause light scatter
  • contrast and filter - certain sports
  • cosmetic
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2
Q

EM Spectrum

A

generally interested in visible light spectrum
UV 100-400nm
Visible spectrum 400-800nm
Infrared (IR) 800+

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3
Q

Spectrum and damage

A
  • UVA linked to cataracts and retinal damage - its quite deeply penetrating
  • UVB linked to cataracts and photokeratitis
  • Visible spectrum can cause disability and discomfort glare
  • IR causes heat cataract and retinal/choroidal burns
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4
Q

UV Protection

A
  • not always provided with tinted lenses
  • its a separate coating
  • clear coating
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5
Q

Mirror Coatings

A
  • supplied with a dark tint to prevent the wearer seeing themselves in the mirror coating
  • tint depth also influences the amount of reflection
  • dont wear well - can get scratched
  • protection from absorption and reflection
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6
Q

Describing Tints

A

-colour
-depth in percentage - light transmission factor (LTF) and absorbance (ABS)
eg an 85% LTF lens is light

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7
Q

What colour

A
  • to enhance contrast eg drivewear and sports tints
  • personal preference
  • cosmesis - frame choice
  • protection - certain colours provide protection
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8
Q

Tints Available

A
  • fixed
  • graduated
  • photochromic
  • polarised
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9
Q

Fixed Tints

A
  • standard tints
    -same colour throughout the lens
  • methods of tinting
    1- Plastic dip dyeing - important lenses are done in pairs
    -diff materials have diff porosities so accept/reject tint easier
    -newer/older lens absorb tint differently

2- Glass - solid/laminated
solid - tint is introduced to lens when its molten
- tint provided depends on metal oxides used in molten mix
laminated - v thin extra sheet

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10
Q

Lamberts Law

A

Thicker the material, the darker the tinting is

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11
Q

Graduated Tints

A
  • can be single or dual coated - theyre darker at top graduating to a lighter colour at the bottom
  • easy to do in plastic
  • advantages: reading, fashion, can be one colour at the top another at the bottom
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12
Q

Photochromic Tints

A
  • darken due to energy provided by UV
  • darker quicker than they turn back to light
  • no separate sunglasses require 0 convenient as no swapping pairs
  • tint variable so comfort at all light levels
  • temp dependent - work better in cold enviros
  • full uv400 protection
  • less reactive behind a uv filter eg car windscreen so they may not get as dark when driving
  • residual colour with age - lenses will look yellow after time, may affect vision in darker conditions
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13
Q

Photo chromic tints for glass

A
  • silver halides - separate when activated by UV

- equi tint (laminate) can be used on high rx

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14
Q

Photo chromic tints for plastic

A
  • pyrans and oxazines in the 100-150 microns of the front surface of the lens
  • molecules rotate on activation by UV and become darker
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15
Q

Polarised

A

unpolarised light - light which vibrates in all directions
polarised light - vibrations restricted to one meridian, can cause glare, polarised in the plane parallel to the reflecting surface
- axis of filter set vertical
-bs tolerance 5 degrees
- done by stretching iodine crystals
- if px complains glare concerns them, use polarised instead of standard tint

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16
Q

IR Lenses

A
  • exposure from sun, furnaces and explosions
  • linked to heat, cataract, retinal and choroidal lesions
  • cant protect with CR39
  • Rayban G15- ferrous oxide - produce a green tint
17
Q

Green tints

A
  • Transmits all colours evenly
  • Dims glare while brightening shadows
  • recommended for all outdoor activities in any weather condition,
  • Rayban G15 is a common eg
18
Q

Brown/Amber tints

A
  • Improves contrast
  • Enhances depth perception
  • Recommended for golf, tennis, any sport when distance needs to be judged.
  • Works best in partly cloudy to sunny conditions
  • Best for weather that changes frequently
19
Q

Yellow tints

A
  • Provides greater clarity in fog, haze, and low light conditions,
  • Filters out blue light that can make focusing difficult
  • Recommended for skiing, mountain biking, hunting
  • May cause colour distortion
  • Good for first and last light and foggy/hazy conditions
20
Q

Purple tints

A
  • Cosmetically appealing
  • Reduces glare
  • Helps sees contours and improves colour perception
  • Recommended for spectator and golf
  • good in misty, foggy and snowy conditions
21
Q

Grey Tints

A

-Anti fatigue
-True colour perception
-Dark enough to provide overall protection, reduces glare, esp off water
Recommended for driving, baseball, tennis, all outdoor activities
-good variable weather tint on sunny/overcast days

22
Q

Pink/ Red tints

A
  • Enhances visual depth
  • Reduces eye strain, provides good road visibility
  • Helps adjust contrast
  • Recommended for cycling, racing and driving
  • Good in most weather conditions, esp in snow