Colours of the visible spectrum
- red, orange, yellow, green, blue, indigo, violet
– photography, animal vision
See also
visible light and colour
and
the structure and function of the eye
The sources and properties of visible
light
I think that the sources are pretty obvious
e.g. natural sunlight, artificial sources like lamps etc.
In these cases you are dealing with excited
energised atoms where electrons fall from a higher to a lower electronic
energy level (shell) the loss of energy given out as visible light EM
radiation.
White light consists of a mixture of all the
colours of the visible spectrum.
Know the colours of the he visible spectrum - red, orange, yellow,
green, blue, indigo, violet
and the trend ==> increasing frequency, decreasing wavelength,
increasing photon energy
The colour of an object depends on
which colours (wavelengths) are absorbed by, transmitted through or
reflected off, the surface of an object. For more details on colour see
...
The uses of visible light
Vision
- our eyes are very sensitive to light enabling our brain to construct an
image of what we are looking at - we take this for granted!
We use artificial light sources to illuminate the surroundings and objects
that we wouldn't see in the dark.
Photography: A camera basically consists of
an aperture (opens/closes) to let a controlled amount of light in and a lens
to collect and focus the light onto a light-sensitive film ('old way') or
electronic photocell screen ('new' digital way).
The amount of light
entering the camera is controlled by the shutter speed (time of exposure to
light) and the width of the aperture (f setting).
The photochemical process of light
sensitive silver compound film has mainly been replaced by light
sensitive screens in digital cameras.
In a digital camera, the signal from
the sensitive photocell is converted into an image that can be
transferred to e.g. a computer for storage, display, transfer to other
devices, further manipulation in software programs and printing out.
An indirect use! Plants use the visible
light of sunlight in photosynthesis and we rely on the plants for food!
BUT, not so indirect if you
deliberately use artificial light in greenhouses growing food on an
industrial scale - the plants can be grown continuously '24/7' to increase
efficiency.
Using
solar cells, visible (and uv) light can be directly converted into
electrical energy with a solar cell - so light is a renewable energy source.
Visible light can also travel down
optical fibres, the effect is used in some 'arty' decorative table lamps as
well as data transfer and communication.
The thin fibre can be made of
glass or plastic and is very long and flexible.
Optic fibre cables work because the
light signal is reflected off the internal surface with very little
absorption or scattering - the light rays literally bounce of the sides
of the fibre even if the fibre is bent - there is little loss due to absorption or scattering
of the wave energy on the side of the fibre optic cable.
The light waves in the fibre are
totally internally reflected off the internal surface and travel along
at the speed of light without being absorbed - the photons just bounce
of the internal surface of the fibre.
Optical fibres are used
for telephone communications and internet cables because you can encode
data onto the beam of light. Optical fibres can transfer
information over very long distances.
Optical fibres often use a single
infrared wavelength/frequency of the carrier wave to reduce loss of information.
The digital information signal is
imposed on this visible light carrier wave.
Optic fibres are also used in
medicine for internal examinations without intrusive surgery - if
necessary, only a small hole is needed. You send light down one set of
fibres to illuminate the tissue and a small camera records the images
and sends the picture back to the observer/computer screen. This helps
diagnose medical conditions. You can of
course also perform microsurgery with an attached small instrument.
The dangers of visible light
Most visible radiation is reflected or
absorbed by the skin.
Very intense visible light can damage
your eyes and people with very 'light sensitive' eyes wear shaded glasses to
reduce the intensity of visible (or uv, see next) light hitting the retina at the back
of the eye.
