safety specs symbols

Question 1

safety glasses impact resistance

Answer 1

S = increased robustness
F = low energy impact
B = medium energy impact (goggles or face shield only)
A = high energy impact (face shield only)

Question 2

8

Answer 2

resistant to electrical charge

Question 3

9

Answer 3

resistant to molten metals

Question 4

K

Answer 4

resistant to fine particles

Question 5

N

Answer 5

resistant to fogging (for 8 secs)

Question 6

G

Answer 6

resistant to radiant heat

Question 7

3,4,5

Answer 7

3 = liquid/droplets
4 = large dust particles
5 = gas, fine dust particles

Question 8

W

Answer 8

can use underwater

Question 9

CR39 advantages + disadvantage

Answer 9

good impact resistance + easily tinted

sharper fragments if shattered

Question 10

polycarbonate advantages + disadvantages

Answer 10

highest impact resistance
lightest material

causes colour fringes
absorbs UV radiation
scratches easily

Question 11

when should polycarbonate lenses not be used?

Answer 11

shouldn’t be used if px works with chemicals or heat

chemicals (specifically alkalis) degrade material i.e., loses impact resistance qualities (shouldn’t be cleaned with alkali products)

Question 12

cellulose acetate

Answer 12

good chemical resistance

poor impact resistance

Question 13

blank size

Answer 13

eyesize plus distance between lenses minus PD + effective diameter + 2 for glazing errors

+3 for supras, +4 for rimless

Question 14

ABBÉ NUMBER

Answer 14

gives value to amount of light dispersed by a material

lower number = bad

Question 15

what happens to lens as refractive index increases?

Answer 15

density and amount of aberration increases - MAR coating for this

weight decreases if plastic (increases if glass)

Question 16

anti reflection coating

Answer 16

very hard thin film layered on the front of lens

layers of metal oxides added to surface of lens to reduce amount of light reflected onto lenses allowing more light to be transmitted through the lens without glare

Question 17

high plus specs closer vs further than trial frame

Answer 17

high plus specs closer than trial frame = more plus

further than trial frame = less plus

Question 18

high minus specs closer vs further than trial frame

Answer 18

high minus specs closer than trial frame = less minus

further than trial frame = more minus

Question 19

AR coating when applied in a thickness of 1/4 of lights wavelength

Answer 19

the two reflections from each side of the film basically cancel each other out through destructive interference

Question 20

H

Answer 20

frame suitable for px with a small head