Photochromic Lenses - FINAL Flashcards
in glass lenses, the darkening agent is _
silver halide crystals
do glass photochromic lenses wear out over time?
no, but they eventually do not return to their lightest state as a they did when new (fatigue dark)
glass photochromic lenses are considered a _ lens
true sunglass
there was a push to plastic photochromic lenses for what reason?
density/weight
_ is the primary examples of photochromic technology using imbibition
transitions
with imbibition, the photochromic molecules are permanently imbedded into the _ surface to a uniform depth
front
with imbibition, the density of color is _
uniform across the surface regardless of rx
gray variable polarized photochromic lens, maximum polarization 85%
transitions vantage
method that mixes the photochromic dyes into the liquid lens material prior to casting
in-mass technology
with in mass technology, lens darkness _
is not uniform - density is not uniform do darkness varies
a drawback of in mass technology?
unable to deliver truly clear performance indoors due to the excessive photochromic dye
with plastic in-mass technology, it lasts long how?
organic dyes near the surface wear out, UV begins to penetrate into the lens deeper and activate photochromic dye
method where lens is dipped and cured with heat
dip coating
coating front surface and UV cured
front-surface coating
transbonding is used with what 3 materials?
trivex, polycarb, and high-index lenses
a clear lens that has a 1mm layer bonded
multimatrix
3 advantages of plastic photochromic lenses:
1) good UV protection
2) uniform density
3) light weight
main disadvantage of plastic photochromic lenses:
life of lens depends hours of wear - problematic when one lens needs replacement
when replacing a plastic photochromic lens, what is recommended?
replace both lenses because they will age differently
are plastic photochromic lenses considered sunglasses?
no
factors that influence performance:
- light intensity -
- temperature -
- previous exposure -
- lens thickness -
both
both
glass
glass
the method that glass lenses are hardened (chemical or heat) affect _
transmission
_ method of hardening the lens is preferred as it yields a darker lens
chemical tempering
photochromic lens get darker on _ days
cold
what is exposure memory with glass lenses?
they reach their full changing range and speed only after a breaking in period
a well used glass photochromic lens will darken _ than an identical new lens
faster
when replacing photochromic lenses, always _
replace in pairs
