Lens enhancement

LENS ENHANCEMENTLENS ENHANCEMENT
OPTOM FASLU MUHAMMED

LENS ENHANCEMENTLENS ENHANCEMENT
There are various kinds of surface treatments
that are applied on either side of the spectacle
lenses
1.Anti-reflection coating (ARC)
2.Scratch resistance coating
3.UV coating
4.Hydrophobic coating

Anti-reflection Coated LensAnti-reflection Coated Lens
Anti-reflection coating are applied on the
lens surface to efficiently manipulate the
light transmission and reflection through it.

THE REFLECTION OF LIGHTTHE REFLECTION OF LIGHT
1.Frontal Reflection
2. Backward Reflection
3. Internal Reflection
4. Corneal Reflection

THE REFLECTION OF LIGHTTHE REFLECTION OF LIGHT

PRINCIPLE OF ANTI-REFLECTIONPRINCIPLE OF ANTI-REFLECTION
COATINGCOATING
To reduce the loss of light due to
reflection and increase the light
transmittance through the lens to
the eyes.
Based on destructive
interference.

PRINCIPLE OF ANTI-REFLECTION COATING

PRINCIPLE OF ANTI-PRINCIPLE OF ANTI-
REFLECTION COATINGREFLECTION COATING

SINGLE LAYER ANTI-SINGLE LAYER ANTI-
The simple principle of single layer anti-
reflection coating is that the substrate
(lens) is coated with a thin layer of
material.

PRINCIPLE OF ANTI-PRINCIPLE OF ANTI-
The refractive index of the coating is the
square root of that of the lens material.
The thickness of the coating, multiplied by
its refractive index, is exactly one –
quarter of a wavelength of light or any odd
number of quarter wavelengths

MULTILAYER ANTI-REFLECTIONMULTILAYER ANTI-REFLECTION
COATINGCOATING
The limitations of the single layer
antireflection coating can be overcome by
multilayer coating which are now capable
of almost extinguishing surface reflections
from one end of the visible spectrum to
the other.
coating may be two layers or more.

In a two layer coating, the outer layer is
made of a low refractive index and the
inner layer is made of a high refractive
index material compared to the
substrate.

ADVANTAGES OF ANTI-ADVANTAGES OF ANTI-
People see better with anti-reflection.
Ghost images, particularly while driving at
night.
Reflections from back lens surfaces can
also be annoying. This is most noticeable
with sun lenses because the dark lens acts
like a mirror.

ADVANTAGES OF ANTI-ADVANTAGES OF ANTI-

TECHNOLOGY OF ANTI-REFLECTIONTECHNOLOGY OF ANTI-REFLECTION
COATINGCOATING
Done inside a vacuum chamber.
The lens to be coated must be
absolutely free of surface defects,
perfectly cleaned and rid of dust or any
other impurities before they are placed
in the vacuum chamber.
glass lenses can be heated up to 300 deg
C/570 deg F, plastics heated above 100
deg C/210 deg F.

HYDROPHOBIC COATINGHYDROPHOBIC COATING
Anti-reflection coating needs to be kept
clean.
This problem can be eased if hydrophobic
coating is applied to the lens surface.
The basic principle is to create a high
surface wetting angle, which allows the
water or oil to run off rather than wetting
and then drying on the surface.

HYDROPHOBICHYDROPHOBIC
COATINGCOATING

HARD COATING orHARD COATING or Scratch-ResistantScratch-Resistant
Coatings (SRC)Coatings (SRC)
Hard coating is a procedure by which a
thin layer of material usually 0.5 micron to
10 micron thick is applied to the lens
surface.
The most common material used is
lacquer which is applied either by dipping
or by spinning procedure.

Thermally Cured Hard Coatings
lenses are dipped in a “varnish” and
removed from the varnish at a consistent
rate to control thickness of the coating.
 The lenses are then thermally cured or
“baked” over an extended period of time.

UV-Cured Hard Coatings
using a system that spins the coating on
the lens.

HARD COATING orHARD COATING or Scratch-Scratch-
Resistant Coatings (SRC)Resistant Coatings (SRC)

UV light comprises approximately 5% of total
solar radiation.
Ozone in earth’s atmosphere absorb almost
all solar UV –C radiation. of the reminder
which strike the earth’s surface approximately
90% is UV-A and 10% is UV-B.
UV exposure may also come from arc
welding and UV emitting light bulbs.
Ultraviolet filtersUltraviolet filters

UV COATINGUV COATING
UV exposure
sunlight, welding arcs, industrial
sources, mercury vapour lamps, tubelight
Conditions
Pterygium, pingecula,cataract,cystoid
macular oedema,skin ageing

IR wavelength near 1400 nm are very
hazardous ;filters for these wavelengths are
usually incorporated into protective goggles
and face masks.
Blue light filters vary in tint between yellow
and red. They increase contrast and facilitate
distinction of light and dark areas and are
used by mountaineers and skiers.

A tinted lens modifies the spectral profile
of the radiation passing through it .
Tints are either absorptive or
reflective ; absorptive tints absorb
light passing through them, whereas a
reflective tint reflects unwanted
wavelengths.
Tinted LensesTinted Lenses

Unequal absorption of different wavelengths
produces a coloured tint. For example , a
yellow tinted filter absorb all wavelengths of
light except those in the yellow part of the
spectrum, which it transmit.
A neutral density filter absorbs all
wavelengths to the same degree and does not
alter the spectral composition of the light.

SURFACE TINTING OF LENSESSURFACE TINTING OF LENSES
Tints are simply the methods of absorbing
lights so that transmission is reduced.
If all wavelengths of light are equally
absorbed, then a neutral grey is produced.
If the absorption is different for different
wavelengths, then the tint has a particular
colour.

The purpose of tinted lenses may be to
screen out unwanted or harmful radiation
(laser protective goggles) or cosmetic.

Varieties of tinted lensesVarieties of tinted lenses

PROCEDUREPROCEDURE
The lenses are placed in a suitable bath of
hot colour dye for an appropriate length of
time.
Glasses can also be coated by vacuum
process which has a unique advantage of
uniform tint throughout the lens surface
which is otherwise not possible in glass
lenses.

Tinting of lensesTinting of lenses
Mixing dye to molten glass material
Blowing layer of coloured glass on the
surface.
Deposition of fine layers of tint on the
surface by vaccum process or electron
beam process.
Deposition of mirror like coating

PHOTOCHROMICPHOTOCHROMIC
LENSESLENSESPhotochromic lenses are lenses that visibly
darken and fade indefinitely under bright
and dull light respectively.
A photochromic glass lens contains billions
of microscopic crystals of SilverHalide.
When exposed to direct sunlight or UV
light, these crystals absorb energy and
cause the formation of metallic silver
deposit on silver halide crystals..

Photochromic lensesPhotochromic lenses
Silver halide
Made up of two types of materials;
borosilicate glass and aluminophospahte
glass.
Transmittance range
 Fading rate
 Reaction time

Darkening process of photochromaticDarkening process of photochromatic
lenslens

TINT OPTIONS INTINT OPTIONS IN
PHOTOCHROMIC LENSESPHOTOCHROMIC LENSES
Glass photochromic lens usually come in
two basic colours – grey and brown.
Technically it is possible to obtain other
tint.

RESIN PHOTOCHROMIC LENSRESIN PHOTOCHROMIC LENS
Photochromic compounds can be
incorporated into a resin lens by applying
either a photochromatic coating or dye
to the lens or by penetration of the
surface, known as imbibitions

PHOTOCHROMIC LENSESPHOTOCHROMIC LENSES

POLAROID LENSESPOLAROID LENSES
The principle of polarized lenses can be
best illustrated by observing Venetian
blinds.
The blinds block lights at certain angles,
while allowing lights to transmit through
it at certain angles.
Polarization implies restricting the light
waves to one direction.

Polarized lenses block horizontally
aligned light which causes glare, while
allowing vertically aligned light to
transmit.

Polaroid lens allows only useful verticalPolaroid lens allows only useful vertical
light waveslight waves

ADVANTAGES OF POLAROIDADVANTAGES OF POLAROID
LENSESLENSES
Filters glares
 Enhances contrast and depth perception
 Reduces eye strain, greater comfort
 Improves visual acuity, provides safety
 Eyes feel rested
Realistic perception
 Reduces reflection
 Comfortable and attractive – looking sun wear.

ADVANTAGES OFADVANTAGES OF

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