Light is a form of energy that can come from a number of sources. Light sources are referred to as bing primary and secondary light sources. Primary light sources include electrical lamps, candles and fires. The primary light source from which we get most of our light here on Earth is the Sun. Secondary light sources are those which reflect light towards and includes the Moon, which, although it often lightens a dark night, is reflecting light from the Sun.
When light from a light source reaches an object it can be:
- transmitted or allowed to travel through, like glass;
- absorbed as in a black surface;
- reflected as in a smooth shiny surface like a mirror.
Materials that allow light to be transmitted can fall into transparent, translucent and opaque.
Reflected light enables us to see objects around us. Light from a light source hits an object and some of that light is reflected and enters our eyes. This then forms an inverted image on the retina at the back of the eye. Impulses are then sent via the optic nerve to the brain where these signals are interpreted as a virtual image. Light only travels in straight lines, so even though we may be able to see objects over huge distances we cannot directly see things that are in a straight line from us.
In the same way that sound levels vary depending on the energy present we can also experience different intensities of light. A light source that transmits large amounts of energy will have a greater intensity or brightness, conversley those with lower energy levels will be less bright. This can be shown in diagram form. Both the diagrams to the right have waves of the same wavelength but different amplitudes. The first represents a low intensity light the second a higher intensity light.
