6. The properties, uses and dangers of visible light

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 visible spectrum of colour, light filters and explaining the colour of objects

 

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The photochemical process of light sensitive silver compound film has mainly been replaced by light sensitive screens in digital cameras.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.