Sunglasses

Aka: Sunglasses

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II. Light Spectrum

  1. IR radiation
  2. Visible light
  3. Ultraviolet Light A (UV-A)
    1. Short wave, High Energy
    2. Screened by ozone
    3. Absorbed by lens
  4. Ultraviolet Light B (UV-B)
    1. "Burning waves"
    2. Absorbed by Cornea and lens
  5. Ultraviolet Light C (UV-C)

III. Prevention

  1. Avoid Peak UV exposure time
    1. 12 noon (1pm at daylight savings)
    2. 3h before or 3h after peak: UV exposure 1/2

IV. Lens Characteristics

  1. Blue light blocking lenses sharpen hazy conditions
    1. Blue light focuses slightly in front of Retina
    2. Part of aging, lens absorbs more blue and UV light
    3. Helps maintain night Vision
  2. Visible light transmission
    1. Glasses that block 2-10% are probably effective
    2. If look in mirror w/ glasses and can't see eyes,
      1. then effective block
  3. UV Blocker
    1. Look at what part of the spectrum is blocked
  4. Infrared blocker
    1. Reduces thermal energy perceived by lens
    2. May be good for Dry Eyes, Contact Lens wearers
  5. Polarizing lens
    1. Effective for water activities

V. Sunglasses

  1. Acrylic-Cheap drug store type
    1. Resolution poor
    2. Shatter into shards in an impact
    3. Scratch easily
    4. Plastic distorts in heat
  2. CR39
    1. Light weight (1/2 as much as glass)
    2. Soft, safe in impact
  3. Polycarbonate
    1. Much stronger than glass, 10x stronger than plastic
    2. Softer, scratch easily
    3. More expensive brands have scratch resistant coating
  4. Glass
    1. Scratch resistant
    2. Breaks easily especially when scratched

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