Light Reflection
Surface type- reflectivity
is a directional property; most surfaces can be divided into those that give
specular reflection and those that give diffuse reflection. Most objects have
some mixture of diffuse and specular reflective properties.
Refractive Index (RI) - by
measuring the angle of incidence and angle of refraction of the light beam, the
refractive index n can be determined. Refractive index of materials varies with
the frequency of radiated light.
Reflective Value (RV) - the
reflective value of a colour indicates how much light and heat is reflected
back from the colour surface. Light reflectance value (RV) is a numerical
rating assigned by paint manufacturers to each colour they make. This number is
a scientifically determined assessment of the amount light and heat that colour
will reflect on a scale of 0 to 100.
Refractive Index (RI) or Haze Value -when
light strikes the surface of a material it bounces off in all directions due to
multiple reflections
Light Reflective Value (LRV) –the
average blackest black has a light reflection value (LRV) of approximately 5%
and the purest white is approximately 85%. Some yellows can measure up into the
80's or 90's as well. All colours fit in between these two extremes.
As can be seen there are
many factors to consider as to what constitutes optimum surface light
reflection, one factor that has the most profound affect is light reflective value
(LRV) or Surface colour
Optimal Light Reflection
Requirements:
- Clean-washed to remove oxidation, surface dirt and grime, tar and road film
- Reflectivity – that comes from a clean and level surface
- Gloss-that comes from oils and polymers with their ability to reflect light with a minimum of light diffusion to produce surface shine
- Optical depth-comes from an applied product that is two-dimensional, so that light is reflected from both a high and low source, (i.e. a Carnauba waxes ‘egg-grate’ type structure) which ‘distorts’ reflected light to produce a rippling effect (warmth)as opposed to a polymer elongated and ‘chain-link’ type mesh, which exhibits a flat ‘mirror’ like shine
- Optimising light refraction -apply product in ‘direction of airflow’, horizontal surfaces hood to trunk, vertical surfaces front to back. This application technique affects the paints optical properties by optimising light refraction and the reflectivity of the bodylines and contours of the vehicle
- Transparency-or clarity of the applied product, which will enable all the above components to be clearly visible
Light Reflection
The way light is reflected
from a paint surface affects the vehicles appearance after it is detailed. Reflection of light is either Specular (mirror-like) or Diffuse (retaining
the energy, but losing the image) depending on the nature of the surface. It is also possible for reflection to occur from the
surface of transparent media, such as water or glass.
Transverse Waves - light
is a form of wave motion, but as it travels at such a high speed it isn't
possible to observe directly the way in which the moving waves vibrate.
However, experiments show that the waves vibrate at right angles to the
direction of the light beam, and because of this light is said to consist of
transverse waves.
Laws of reflection- if the reflecting surface is very
smooth, the reflection of light that occurs is called specular or regular
reflection. The laws of reflection are as follows:
The incident ray -the reflected ray and the normal to the
reflection surface at the point of the incidence lie in the same plane.
The angle - which the incident ray makes with the
normal, is equal to the angle which the reflected ray makes to the same normal.
The way light is reflected
from a paint surface affects the vehicles appearance after it is detailed. Reflection of light is either Specular (mirror-like) or Diffuse (retaining
the energy, but losing the image) depending on the nature of the surface. It is also possible for reflection to occur from the
surface of transparent media, such as water or glass.
1.
Paint colours reflect light differently, i.e. a white or silver
will reflect specular light. Darker colours i.e. red, black, etc absorb light
and therefore the reflected light is diffused.
2.
Metallic paint reflects light from the flakes, which create micro
mirrors and add a distinctive ‘shine’
3.
A polymer sealant or a nano coating product are more suited to
the reflectance properties of light colours. An organic wax suit the reflective
properties of darker colours due to its imparted jetting (wet-look)
Surface type
Reflectivity is a
directional property; most surfaces can be divided into those that give
specular reflection and those that give diffuse reflection. Most objects have
some mixture of diffuse and specular reflective properties.
For specular surfaces-
such as glass or polished metal, reflectivity will be nearly zero at all angles
except at the appropriate reflected angle.
For diffuse surfaces - such
as matte paint, reflectivity is uniform; radiation is reflected in all angles
equally or near-equally. Such surfaces are said to be Lambertian.
Spatial reflection – [:direction of incoming light (the
incident ray), and the direction of outgoing light reflected (the reflected
ray) make the same angle with respect to the surface normal, thus the angle of
incidence equals the angle of reflection; this is commonly stated as θi = θr.]
The perfect, mirror-like
reflection of light from a surface, in which light from a single incoming
direction is reflected into a single outgoing direction the best example of
spatial reflection is seen when reflected from a flat level surface.
If the surface is perfectly
flat, light will be reflected to produce a mirror image of the surface. But if
there you have matte paint or are imperfections such as swirls, surface
contaminants, orange peel, or oxidation (dull, opaque or unlevelled paint)
light is refracted and the reflected light becomes distorted, which mutes the
shine.
Diffuse
reflection [:
incoming light is reflected in a broad range of directions] [1]
When light strikes the
surface of a material it bounces off in all directions due to multiple
reflections.. The most familiar example of the distinction between specular and
diffuse reflection would be glossy and matte paints.
While both exhibit a
combination of specular and diffuse reflection, matte paints has a higher
proportion of diffuse reflection and glossy paints have a greater proportion of specula
reflection. [1]
Reflective Value
[: a
measurement commonly used in interior decorating and design, which expresses
the percentage of light that is reflected from a surface]
The reflective value (RV) of
a colour indicates how much light and heat is reflected back from the colour
surface. Light reflectance value (RV) is a numerical rating assigned by paint
manufacturers to each colour they make. This number is a scientifically determined
assessment of the amount light and heat that colour will reflect on a scale of
0 to 100. Zero assumed to be an absolute black and 100% being an assumed
perfectly reflective white. An absolute black or perfectly reflecting white do
not exist in our everyday terms.
Polymer sealant- comprises
an open linked molecule, which forms a bond with the paint; these open linked
polymer molecules join together to create an elongated mesh like effect that
reflects light efficiently due to their inherent flat surface. Because they are
usually very transparent they transmit the surface colour faithfully, but they
have very little depth resulting in what is perceived as a very bright, but
flat silver glow
A wax or sealant can only
reflect what is underneath it, so a clean, level well-prepared surface is the
most important consideration (85% of a surfaces reflectivity is due to its
preparation) along with applied product clarity. If you apply a product over a
surface that is dirty or one that has surface imperfections a wax or sealant
will not hide or disguise (unless they contain fillers) but highlight them as
the light will reflect differently from the rest of the paint surface.
Refractive Index
By measuring the angle of
incidence and angle of refraction of the light beam, the refractive index n can
be determined. Refractive index of materials varies with the frequency of
radiated light.
This results in a slightly
different refractive index for each colour. The index of refraction
characterizes not only the light propagation speed, but also the bending angle
and the amount of radiation transmitted and reflected by a material
Refractive Index (RI) or
Haze Value -when light strikes the surface of a material it bounces off in all
directions due to multiple reflections. The most familiar example of the
distinction between specula and diffuse reflection would be a polymer and a
Carnauba wax.
While both exhibit a
combination of specular and diffuse reflection, Carnauba wax has a higher
proportion of diffuse reflection and Polymers have a greater proportion of
specula reflection.
•
Mirror (specular) – RI: 1.00
•
Water - RI: 1.33.
•
Carnauba wax (diffuse) – RI: 1.45
•
Polyurethane (Dimethylsiloxane)
(specular) – RI: 1.48
Light Reflective Value (LRV)
The average blackest black
has a light reflection value (LRV) of approximately 5% and the whitest white is
approximately 85%. Some yellows can measure up into the 80's or 90's as well.
All colours fit in between these two extremes.
A colour with an LRV of 50
will reflect 50% of the light that falls on it, and one with an LRV of 23 will
reflect 23% of the light, and so on. Think of a reflective value as a numerical
version of a grey value scale for colours, roughly like this-
Pure White -
100, White -95, Light - 80,
Low Light - 65, Medium -
50, High Dark - 35, Dark – 20
It would take too long to
list individual OEM colours, i.e. Arctic White, Speed Yellow, Guardsman Red,
Onyx Black, etc so you’ll need to interpolate
As can be seen there are many factors to consider apart from
index numbers
Shine vs. Gloss
The reflective value (RV) of
a colour indicates how much light is absorbed or diffusely scattered dependent
on the colour.
·
High
reflective value (i.e. white or very light colours) exhibit Spatial (Shine) reflection; a mirror-like
reflection from a surface
·
Low
reflective values (i.e. darker colours (black) exhibit a diffused (Gloss) reflection; incoming light is reflected in a broad range of directions
Backlighting
Clear coated
paints show minor swirls and scratches more readily than pigmented paint
(single stage) due to an optical effect called backlighting. Light penetrates
the clear coat and is reflected from pigmented paint (colour coat) which in
turn reflects any imperfections in the surface of the clear coat, making them
highly visible.
As you drive towards the setting sun or
oncoming headlights on a rainy night, every speck of dirt, smudge or smear on
your windshield is suddenly very obvious. They are much more noticeable when
sunlight or oncoming headlights back-light them.
Light Coloured Surface
For secular
surfaces, such as glass or polished metal, reflectivity will be nearly zero at
all angles except at the appropriate reflected angle. For diffuse surfaces,
such as matt white paint, reflectivity is uniform; radiation is reflected in
all angles equally or near-equally. Such surfaces are said to be Lambertian.
Most objects have some mixture of diffuse and secular reflective properties.
Reflection
Reflection and refraction are terms that describe
how is reflected from a surface; refraction or diffused reflection) changes due to the
microscopic irregularities of the surface, each medium has a different
reflective value.
As light travels and strikes the paint surface, it travels through the wax or
sealant then the clear coat it reflects at different angles due to their
differing reflective values.
It will also
reflect back at certain points where the angle of incidence equals the angle of
reflection. As the photons of light gain proximity they become more brilliant.
To enhance gloss you need to reflect as much light as possible, without
interfering with that proximity or brilliance.
Proving the reflective surface is level, a rotary
would produce a circular pattern, and a random orbital would produce an
elliptical pattern, which would tend to separate the photons, thus reducing
brilliance, while the circular would combine and concentrate them, thus
enhancing gloss.
Intensity is dependent on
the material and the angle of illumination. In case of non-metals (coatings,
plastics) the amount of reflected light increases with the increase of the
illumination angle. The remaining illuminated light penetrates the material and
is absorbed or diffusely scattered dependent on the colour.
Gloss Measurement
Surface
gloss [: is considered to be the amount of
incident light that is reflected at the specular reflectance angle of the mean
of that surface.]
Materials with a higher
refractive index can have a measurement value above 100 gloss units (GU), e.g.
films. In case of transparent materials the measurement value can be increased
due to multiple reflections in the bulk of the material. Due to the high
reflection capabilities of metals values of up to 2000 GU can be reached.
Gloss is a visual impression
resulting from surface evaluation. The more direct light reflected, the more
obvious the impression of gloss will be. Smooth and highly polished surfaces
reflect images distinctly. The incident light is directly reflected on the
surface, i.e. only in the main direction of reflection. The angle of incidence
is equal to the angle of reflection.
For these applications it is
common to document the measurement results in % reflection of the illuminated
light - 60 degree Gloss Meter (approx $2,500 -05/2011) -
Micro-Gloss 60, Model SGB-4460
Colour, Depth and Clarity
[:
Reflectivity is the fraction of incident radiation reflected by a surface. In
full generality it must be treated as a directional property that is a function
of the reflected direction]
Are the three factors
Concours d’elegance judges look for when scrutinizing paint film surfaces. So
much depends on proper surface preparation, a clean and level surface, and
product clarity, which allow the natural properties of the paint to show
through, as without transparency the true colours of the paint surface cannot
be seen. Waxing a surface that has not been properly cleaned will only result
in a shiny layer over dull, dirty paint - not the deep smooth, optically
perfect crystalline shine that is obtainable
Gloss - is an
optical property, which is based on the interaction of light with physical
characteristics of a surface. It is actually the ability of a surface to
reflect light into a specular direction. The factors that affect gloss are the
refractive index of the material and the angle of incident lighting.
The
oils that are formulated in Carnauba waxes provide gloss, which causes jetting
(a ‘wetting’ of the surface) this distorts the light reflectance, giving the
surface the ‘look’ of depth or liquidity (i.e. mirror in shallow water
reflecting a three-dimensional deep, rich colour)
Depth – (iridescence)
occurs due to the internal reflection of light within a transparent film or
layer of material, where the thickness of the film or layer is of the order of
the wavelength of the incident light.
Where
the wavelength of the light matches or is a low multiple of the path length
through the layer it will re-emerge from the layer after a single reflection
but where the wavelength is different to the path length it will be
re-reflected within the layer until it emerges after several internal
reflections. Changing your viewpoint changes the path length through the layer
and this means that a different wavelength or colour of light will seem to be
reflected.
Chromatics - the science of colour is sometimes called
chromatics. It includes the perception of colour by the human eye and brain,
the origin of colour in materials, colour theory in art, and the physics of
electromagnetic radiation in the visible range (that is, what we commonly refer
to simply as light).
Optical depth-comes from an applied product that is
two-dimensional, so that light is reflected from both a high and low source,
the light waves are distorted (diffuse
reflection) which creates a three dimensional illusion of depth to produce
jetting (a rippling effect, the so-called ‘wet-look)
The oils that
are formulated in Carnauba waxes provide gloss, which causes jetting (a
‘wetting’ of the surface) this distorts the light reflectance, giving the
surface the ‘look’ of rippling liquidity, like a mirror in shallow water
reflecting a three-dimensional deep, rich colour, in contrast, bees wax,
paraffin and many synthetic waxes and polymer sealants tend to occlude (cloud)
Shine – a
perfectly ‘flat’ levelled surface is obtained by polishing the paint
surface. Shine an easily understood concept of light reflection / refraction
(in simple terms the light reflectance from a mirror) I wanted to expand that
concept so that the shine would be optically perfect as well as
multi-dimensional. The bright shine of a polymer sealant is often criticized as
being “sterile” (a flat silvery-white reflection) good reflective properties
but without ‘depth’ or jetting (wet-look) of an organic wax.
·
Optimising light refraction - apply product in ‘direction of
airflow’ to vertical surfaces roof to floor and then left to right, on
horizontal surfaces bumper to trunk and then left to right, over-lapping panels
to ensure complete coverage. Then apply in direction of airflow, horizontal
surfaces hood to trunk, vertical surfaces front to back. This application
technique affects the paints optical properties by optimising light refraction
and the reflectivity of the body lines and contours of the vehicle.
·
The aesthetics- of a vehicles appearance is very subjective to
say the least, the only best wax or sealant that really matters is what looks
'best' to you. In the final analysis it all come down to; 85% preparation, 5%
product, 7% application method and the balance is in the ‘guy’ of the beholder
·
Optically Clarity – [: its
refractive index (RI) allows a majority of the incidental light to be
transmitted] [The term ‘optical clarity’ is difficult to
define, and the boundaries between ‘transparent’ or ‘clear’ and ‘translucent’
or ‘opaque’ are often highly subjective. What is acceptable for one observer is
possibly not acceptable for another observer.] Zeus website
·
An optically perfect shine comes from a clean, clear (i.e. the
applied products do not occlude the surface underneath) prepared and level
surface; it improves the desired optical properties i.e. surface reflectance.
The other requirements are surface gloss, depth of shine and applied product
transparency (clarity), which allows all of the components of an optically
perfect shine to be visible.
·
The best light reflection is obtained from a perfectly flat
highly reflective surface, i.e. glass over a silver metallic material(a mirror)
·
A polish would need to level a paint surface; this will provide
a surface without distortion
·
To provide protection to our theoretically perfectly
distortion-free surface we would need to apply a wax or a polymer sealant,
which in turn would need to be optically clear
Shine is an
easily understood concept of light reflection / refraction (in simple terms the
light reflectance from a mirror) I wanted to expand that concept so that the
shine would be optically perfect (a majority of the incidental light is
transmitted) as well as multi-dimensional. The bright shine of a polymer
sealant is often criticized as being “sterile” (a flat silvery-white
reflection) good reflective properties but without ‘depth’.
A clean polished paint
surface will exhibit a bright shiny finish, which is great on light colour
paint. On darker colours I prefer not just a bright shine but rather a deeper,
darker gloss.
Similar to a car's black
paint rippling as if it was under water. Carnauba in today's wax formulas
functions as a carrier, it is used to keep the polymers and oils on your car's
surface. Only a small portion of your vehicle's shine comes from the
"wax" (i.e. carnauba) itself. Carnauba is translucent at best with
only minimal light reflection.
The oils that
are formulated in Carnauba waxes provide gloss, which causes jetting (a
‘wetting’ of the surface) this distorts the light reflectance, giving the
surface the ‘look’ of a mirror in shallow water reflecting a three-dimensional
deep, rich colour, in contrast, bees wax, paraffin and many synthetic waxes and
some polymer sealants tend to occlude (cloud) the finish
The aesthetics- of a vehicles appearance is very
subjective to say the least, the only best wax or sealant that really matters
is what looks 'best' to you. In the final analysis it all come down to;
85% preparation, 5% product, 7% application method and the
balance is in the ‘guy’ of the beholder
In obtaining the ‘optically
perfect shine’ we should be equally concerned with ease of application,
resistance to abrasion, atmospheric contamination and weathering. Products
should be chosen that would carefully balance each of these considerations
without focusing on one specific characteristic. A surface protection with a
spectacular shine but limited durability just doesn't make sense.
a) Requirements:
·
Clean-washed to remove oxidation, surface dirt and grime, tar
and road film
·
Reflectivity – that comes from a clean and level surface
·
Gloss-that comes from oils and polymers with their ability to reflect light with a minimum of
light diffusion to produce surface shine
·
Optimising light refraction -apply product in ‘direction of
airflow’, horizontal surfaces hood to trunk, vertical surfaces front to back.
This application technique affects the paints optical properties by optimising
light refraction and the reflectivity of the bodylines and contours of the
vehicle
·
Transparency-or clarity of the applied product, which will
enable all the above components to be clearly visible
b) Contributing factors:
·
Cleaned-
using a mildly alkaline (pH 7.5) car wash concentrates to remove surface road
dirt and grime and then- using detailer’s clay to remove ingrained pollution
from the paint surface, and a chemical paint cleaner (Klasse
All-In-One) to prepare the surface for a polymer sealant and a Carnauba
wax.
·
Polished-removal
of minor blemishes, surface scratches, swirl marks and water marks with an
abrasive machine polish or compound (Menzerna) to
provide a level surface. A machine polish should remove surface imperfections
and swirl marks, contain oils for lubrication and should not leave residue that
requires extensive ‘clean-up’ to remove hazing, its solvents should evaporate
moderately quickly without leaving excess wax/oils behind, and lastly should
buff relatively easily.
·
Glazed- to
obtain a high gloss by providing the necessary oils and burnishing the paint
surface to a high optically clear gloss
·
Protected- the
polymers carrier system (solvents) allows the product to fill and level the
paint film surface to produce an ultra-flat surface while proving durable
surface protection. A polymer (Zanio Z2PRO™) with
its levels of shine, gloss, clarity, reflectivity, depth and 99% optical
clarity, which doesn’t distort or detract from the paints colour or lines of
the vehicle.
·
Waxed-the
applications of Carnauba (Souverän Paste Wax) that will provide oils to
provide a ‘wet-look’ to the surface and will also provide a transparent surface
when layered without yellowing or discoloration, with a depth of shine by
providing a two-dimensional surface.
·
Light
coloured paint -i.e. Silver, White, etc (the exception is speed yellow) will
never obtain jetting (the so called ‘wet-look’) of black or dark colours
as they do not exhibit visible depth,
light colours tends to reflect light instead of absorbing it and providing a
2-dimensional look. You can obtain a good gloss provided the paint is good
quality and if it’s prepared and detailed correctly; washed, cleaned, polished
and a polymer sealant added (Zaino or
Klasse AIO and SG, Jeffswerkstatt - Acrylic Jett ) these
sealants will provide a flat silvery-white shine, but without ‘depth’ the
exception is Zaino Clear Seal
(Z-CS).
By adding a Carnauba wax or a Glaze as an LSP (Pinnacle
Souverän Paste Carnauba or Autoglym Super Resin Polish or Danase
Wet Glaze) the oils and / or polymers that are formulated in the Carnauba
waxes provide a reflective gloss, which causes jetting (a ‘wetting’ of the
surface) For optimal results the surface of a light coloured paint to show
gloss is very much dependent upon good / excellent paint condition, adequately
prepped to remove contaminants and minor imperfections.
Detailer’s clay (Sonus
SFX Ultra-Fine Detailing Clay Bar) and / or Paint cleaner (Zaino
PC or Klasse AIO) should be a regular part of the preparation process
Always be
willing to learn; because the more you learn, the more you’ll realize what you
don’t know.
It is said that knowledge is power, with the caveat that
it includes access to a reliable information sources. I would like to think that these articles become an asset to
anyone who is new to detailing and to professional’s alike, as well as industry
experts who seek to advance their knowledge.
I hope the
article are informative. By having some understanding of the ‘What’ and ‘Why’
as well as the ‘How’ along with a little science to help you understand how the
chemicals we use react, you can achieve the results you desire.
I would appreciate it if you would share
these articles as it helps other detailers further their knowledge.
Questions and/ or constructive comments
are always appreciated.
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© 2002 - 2012 TOGWT® (Established 1980) all rights reserved
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