L3 Light Attenuation

Question 1

types of light attenuation

Answer 1

• mirror coated lenses
• tinted lenses (solid, surface)
• photochromic lenses
• polarizers

Question 2

describe mirror coat

Answer 2

• glass and plastic ok!
• uniform layer/even appearance
• reduces light transmittance by reflectance

Question 3

Describe tinted lenses

Answer 3

• solid mainly for glass lens only
• solid tint becomes more uneven with thicker lenses
• surface only for plastic lens
• reduces light transmission by absorption
• all tinted have glare/uv protection

Question 4

Describe photochromic lenses

Answer 4

• reversible change of colour when electromagnetic energy absorbed
• glass and plastic lens ok
• affected by TEMPERATURE, the cooler the darker
• the hotter, the faster it fades
• less reactive over TIME
• does not react much in car since windshields and windows UV coated hence low levels of uv and light

Question 5

Describe polarizers

Answer 5

• horizontally polarised light (light reflected from polished flat surface or smooth water surface) blocked by vertical,y oriented polarizer filter in lens
• glass and plastic ok
• reduces glare
• PILOTS CANNOT WEAR

Question 6

Relationship between tinted lenses and density of tint

Answer 6

The darker the tint, the lower the light transmittance

Eg. Lens with 85% tint, absorbs 85% of light, light transmission of 15%

Question 7

Why do all tinted sunglasses provide glare protection

Answer 7

Dark lenses causes the pupil to expand, letting in even more UV light.

Question 8

Describe 2 specialty filters

Answer 8

Yellow - increases contrast when hazy (absorbs blue end of spectrum)

Purple - absorbs yellow light to absorb discrimination of blue and red. *glass blowers to see heated glass against yellow flame

Question 9

Types of tint

Answer 9

Gray - glare protection, able to see colours in their natural state bc of even transmission for whole spectrum

Brown - good for both uv and ir absorption

Green - closely appropriates colour sensitivity, good for both uv and ir absorption. Good for outdoor/ golfing

Red/yellow - increase contrast but has colour imbalances. For cycling

Question 10

How to increase UV protection

Answer 10

UV coat (transparent) for plastic lens (CR39)

Add mineral oxides into glass lens mixture to absorb UV