Factors that affect Light Reflection
Reflection
[: is either specular (mirror-like) or
diffuse (retaining the energy, but losing the image)]
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.
Distinctness of image (DOI) - the
appearance of reflecting objects is determined by the way the surface reflects
incident light. The reflective properties of the surface can be characterized
by a closer look at the (micro)-topography of that surface.
Structures on the surface
and the texture of the surface are determined by typical dimensions between
some 10 mm and 0.1 mm (the detection limit of the human eye is at ~0.07 mm).
Smaller structures and features of the surface cannot be directly detected by
the unaided eye, but their effect becomes apparent in objects or images
reflected in the surface. Structures at and below 0.1 mm reduce the DOI
structures in the range of 0.01 mm induce haze and even smaller structures
affect the gloss of the surface.
DOI meter measures the gloss
and the distinctness of image (DOI) of a painted surface for quality evaluation
of the finish. A signal is obtained by a prior method of focusing the reflected
image of a moving shutter onto a slit and measuring the light passing through
the slit. The rate of increase of the resulting signal is used as a measure of
DOI. The same signal is integrated over a pre-set time period covering the
upper part of the signal rise to yield a value proportional to gloss.
Calorimetric and colour theory -
colourfulness, chroma, and saturation are related but distinct concepts
referring to the perceived intensity of a specific colour.
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 (the so-called 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 specula and
diffuse reflection would be glossy and matte paints.
While both exhibit a
combination of specula and diffuse reflection, matte paints has a higher
proportion of diffuse reflection and glossy paints have a greater proportion of specula
reflection.
Refraction
[:
index of refraction n = c / v]
When light travels from one medium to another, the speed changes, as does the wavelength, the index of refraction can also be stated in terms of wavelength: Although the speed changes and wavelength changes, the frequency of the light will be constant. The frequency, wavelength, and speed are related by Snell’s law:
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
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
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 specula 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
•
Poly (Dimethalsiloxane) (specula) – RI: 1.48
The Angle of Rejection
When light reflects off of a
surface such as a mirror, two angles are created from the light’s path and the
surface of the mirror: the angle of incidence and the angle of reflection.
Light Reflective Value (LRV)
The average blackest black
has a light (polarized) reflection value (LRV) of approximately 5% and the
whitest white (un-polarized reflection) 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.
Gloss
Meter
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
A
gloss meter is an instrument which is used to
measure specular reflection gloss of a surface. Gloss is determined by
projecting a beam of light at a fixed intensity and angle onto a surface and
measuring the amount of reflected light at an equal but opposite angle.
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.]
Specular
- means mirror-like and specular gloss is defined as the
perception by an observer of the mirror-like appearance of a surface. In truth
this appearance cannot be quantified: all that can be done instrumentally is to
measure the amount of incident light that is reflected at a defined angle (or
range of angles).
Measurement angle refers to
the angle between the incident and reflected light. Three measurement angles
(20°, 60°, and 85°) are specified to cover the majority of industrial coatings
applications. The angle is selected based on the anticipated gloss range, as
shown in the following table.
For example, if the
measurement made at 60° is greater than 70 gloss units (GU) the measurement
angle should be changed to 20° to optimise measurement accuracy. Three types of
instruments are available on the market: 60° single angle instruments, a
combination of 20° and 60° and one type that combines 20°, 60° and 85°.Materials
with a higher refractive index can have a measurement value above 100 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.
Gloss units - the measurement scale, GU,
of a gloss meter is a scaling based on a highly polished reference black glass
standard with a defined refractive index having a specular reflectance of 100GU
at the specified angle. This standard is used to establish an upper point
calibration of 100 with the lower end point established at 0 on a perfectly
matte surface. This scaling is suitable for most non-metallic coatings and
materials (paints and plastics) as they generally fall within this range.
Two high gloss surfaces can
measure identically with a standard gloss meter but can be visually very
different. Instruments are available to quantify orange peel by measuring
Distinctness of Image
(DOI) or Reflected Image Quality
(RIQ) and Haze.
Rhopoint IQ Flex 20 is
designed for the measurement of small and curved surfaces. This instrument
quantifies surface quality problems such as orange and peel and haze that are
invisible to a standard gloss meter and profiles how light is reflected from a
surface.
Previously gloss meters were
only available for measuring flat surfaces, this technology is now available in
a new format specifically designed for curved surfaces and small & delicate
parts.
Features:
·
Data Widget, which allows results to be instantly transmitted to
any PC package such as Excel, Word, and SPC programs etc.
·
Bluetooth Compatibility that can transmit data to any
smartphone, tablet or PC.
·
USB results download to PC without the need to install software
Reading shown:
Gloss: A measurement proportional to the amount of light
reflected from a surface measured at 20° (high gloss)
Haze: (reflectance haze) an optical effect caused by microscopic
textures or residue on a surface.
RIQ: Used to quantify effects such as orange
peel and surface waviness. This new parameter gives higher resolution results
compared to Distinctness of Image
DOI: A measure of how clearly a reflected image will appear
in a reflective surface and better mimic’s human perception of surface texture,
especially on high quality finishes such as automotive paint finish.
RSPEC: The peak gloss value over a very narrow angle.
Rhopoint
IQ Flex 20 - http://www.rhopointinstruments.com/product/rhopoint-iq-flex-20/
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’élégance 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 bodylines 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 comes 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 paint
protection finish that really matters is what looks 'best' to you. In the final
analysis it all comes 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-dimentional 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).
Bibliography
1.
Gloss as an aspect of the measurement of appearance by W Ji, MR
Pointer, RM Luo, J Dakin
2.
Surface correlation effects on gloss by R Alexander-Katz, RG
Barrera - Journal of Polymer Science
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