C. Light from a red laser passes more easily through red
cellopahne than green cellophane
What is Color?
• You can think of light asa being a kind of
wave, similar to waves in the sea. the
distance between one wace crest and the
net is known as the WAVELENGTH.
DIFFERENT colors have different wavelengths
The wavelength of RED LIGHT is just under
one 5000 of an inch, while violet light just
over on 1 0,000 of an inch. All the other
colors fall somewhere between these two
extremes.
Sunlight or the light an electric bulb
seems colorless, we cll it “white
light”. But in fact it contains the
full range or SPECTRUM of colors
from RED through orange, yellow,
green, blue and indigo to violet.
When these color pass from air to
water or glass, they are slowed
down and refracted by different
amounts. RED LIGHT is bent the least,
violet light are the most.
A FILTER is a material such as
colored cellophanes or
glass, that only lets light of
particular color pass
though. This means that a
red object appear bright
when seen through a red
filter but an object of
another color seems dark
• If you look through a
green cellophane,
everything on the
other side appears
to be shades of
green.
• If you look through a
red glass, everything
appears to be red.
•
• Green cellophane will only allow green light to pass
through it, the cellophane absorbs other color of light.
As a general rule, each color
filter will only allow light of its
own colour to pass through.
D. Clothing of certain colors appear different in artificial light
and in sunlight
Sunlight and fluorescent (artificial) light both appear as “white light,”
they each contain slightly different mixtures of these varying wavelengths.
When sunlight and fluorescent light (white light) are absorbed by a piece of
clothing, only some of the wavelengths (composing white light) reflect off
the clothing. Light is made up of wavelengths of light, and each wavelength
is a particular colour. The colour we see is a result of which wavelengths
are reflected back to our eyes.
• White light is actually made of all of the colours
of the rainbow because it contains all
wavelengths, and it is described as
polychromatic light.
• Objects appear different colours because they
absorb some colours (wavelengths) and reflect or
transmit other colours. The colours we see are the
wavelengths that are reflected or transmitted.
For example, a red shirt looks red because the dye molecules in the fabric have absorbed
the wavelengths of light from the violet/blue end of the spectrum. Red light is the only light
that is reflected from the shirt. If only blue light is shone onto a red shirt, the shirt would
appear black, because the blue would be absorbed and there would be no red light to be
reflected.
White objects appear white
because they reflect all
colours. Black objects
absorb all colours so no light
is reflected.
CRI stands for color rendering index. CRI measures and
compares (on a scale of 0 to 1 00) the ability of a light source to
accurately reproduce the color of an object under artificial light.
An LED bulb that perfectly replicates the sun has a CRI of 1 00,
allowing objects to appear clearly, and naturally, and colors to
appear truer across a wide spectrum. Surprisingly, halogen and
incandescent bulbs, despite their awful energy efficiency,
produce a full, natural and excellent light spectrum with a CRI of
1 00.
We all know every light source is not the same. An object
may reflect slightly different shades of color under
different artificial lights like LED lighting, incandescent
bulbs, and fluorescent and halogen light sources.
In simple terms, the closer the light source is to natural
daylight, the more accurate the color rendering you see
on the object. A red dress under a fluorescent light may
not seem as radiant as it will in natural sunlight.
The following illustration will help you understand how the color rendering
capability of an artificial light source affects what we see as a result. The color
appearance of an object under consideration significantly deteriorates under a low
CRI LED bulb.
E. Haloes, sundogs, primary rainbows, secondary rainbows, and
supernumerary bows.
Haloes
Haloes are coloured or white rings or arcs in the sky usually near
the moon or sun. (Have you ever wondered why there is a white arc
formed around the moon or sun? These are called haloes. Haloes
are coloured or white rings or arcs in the sky usually near the moon
or sun when the temperature in the atmosphere is low.) Formed due
to either refraction and dispersion or reflection of light as it enters
hexagonal ice crystals suspended in the clouds.
• Refraction and
Dispersion: As light
enters the ice crystal, it
is refracted.
• As it leaves the crystal, it is
once again refracted at 22°
and dispersed into different
colors.
• In this case, the arcs or rings
are composed of different
colors.
Reflection:
Instead of being refracted, the light is
reflected at 22 °.
In this case, the ring is just white.
Haloes
Circular arcs are formed when light
strikes the ice crystal at different
angles, taking all the possible
orientation.
Sundogs
Spots of colors beside the sun or moon.
• Formed due to refraction of light as it enters the
hexagonal ice crystal.
• The collective refracted lights at 22 ° formed
sundogs.
Primary Rainbow
Rainbow is a result of reflection, refraction,
and dispersion of white light as it encounters a
water droplet.
• As white light strikes water droplet, some is
reflected.
• Some is refracted as the light enters the
front surface of the droplet.
• Inside the droplet, the white light is
dispersed into several colors.
• As the light reaches the other side of the
drop, the light is reflected towards one
side of the droplet.
• The light is once again
refracted as it moves from
the droplet to air.
Secondary Rainbow
• Secondary rainbow is
fainter and larger than a
primary rainbow with
colors in reverse order.
• Result of two refractions,
two reflections and
dispersion of light.
• As light enters into the
water droplet, it is
refracted.
• Inside the water droplet,
the white light is dispersed
its component colors.
• From point a, the light will then be
reflected towards point b.
• From point b, the light will
be reflected again towards
point c.
• Finally, as the light exits
the water droplet, it is
refracted once again.
Supernumerary Bows
• Extra bands inside a primary
rainbow.
• Results of interference of light
from water droplets of the
same size.
• During
interference,
light
waves which are misaligned,
cancel each other out.
• Light waves aligned with other
combinations
of
waves,
forming the additional bands.
Summary:
• Haloes - Colored arcs: Refraction and Diffraction White Arc:
Reflection
• Sundogs - Refraction of light
• Primary Rainbow - Refraction, Reflection, Dispersion
• Secondary Rainbow - Two refractions, Two reflections,
dispersion
• Supernumerary Bows - Interference
F. Why clouds are usually white and rainclouds dark
What causes clouds?
A cloud is defined as 'a visible aggregate of
minute droplets of water or particles of ice or
a mixture of both floating in the free air'. Each
droplet has a diameter of about a hundredth
of a millimeter and each cubic meter of air
will contain 1 00 million droplets. Because the
droplets are so small, they can remain in
liquid form in temperatures of -30 °C. If so,
they are called supercooled droplets.
Cloud formation:
Clouds form when the invisible
water vapor in the air condenses
into visible water droplets or ice
crystals. For this to happen, the
parcel of air must be saturated,
i.e. unable to hold all the water it
contains in vapor form, so it
starts to condense into a liquid
or solid form.
Why are clouds white?
Clouds are white because light from the Sun is white. As light passes through a cloud,
it interacts with the water droplets, which are much bigger than the atmospheric
particles that exist in the sky.
When sunlight reaches an atmospheric particle in the sky, blue light is scattered away
more strongly than other colours, giving the impression that the sky is blue.
But in a cloud, sunlight is
scattered by much larger
water
droplets.
These
scatter all colours almost
equally meaning that the
sunlight
continues
to
remain white and so making
the clouds appear white
against the background of
the blue sky.
So why are clouds sometimes grey?
Cloud bases are often grey as a result of the same scattering that makes
them white. When light is scattered in a cloud it usually is sent back
upwards, or out to the sides of the cloud, making the tops and sides of the
cloud whiter than the base which receives less light.
This is more prominent in rain clouds because the cloud droplets are bigger,
thus scattering more light. This means that even less light from the Sun
reaches the bottom of the cloud, giving rain clouds their intimidating
appearance.
Rain clouds are gray instead of
white
because
of
their
thickness, or height. That is, a
cloud gets thicker and denser
as it gathers more water
droplets and ice crystals — the
thicker it gets, the more light it
scatters, resulting in less light
penetrating
all
the
way
through it.
References:
https://www.sciencelearn.org.nz/resources/47 -colours-of-light
https://energyperformancelighting.com/whats-cri/
https://rclite.com/blog/color-rendering-index/
https://www.weather.gov/source/zhu/ZHU_Training_Page/clouds/cloud_development/clouds.htm
https://www.livescience.com/39069-why-are-rain-clouds-dark.html
https://www.scribd.com/presentation/534485099/WHY-LIGHT-FROM-THE-RED-LASER-PASING-EASILY-THROUGH-RED-CELLOPHANE-THANGREEN