PROPERTIES OF LIGHT
Wavelength: the distance between successive peaks or troughs
Frequency: the number of waves per second
Amplitude: the difference between wave trough and peak
The energy content of electromagnetic radiation is proportional to its frequency [i.e. high
frequency (short wavelengths) has the highest energy content].
Only a small part of the electromagnetic spectrum is detectable by our visual system.
This visible light consists of wavelengths of 400-700 nm. (see Fig. 9.2)
“Hot” colours (e.g. red or orange) have long wavelength light and less energy than “cool”
colours (e.g. blue or violet).
In a vacuum, a wave of electromagnetic radiation will travel in a straight line. This is a ray.
Reflection: the bouncing of light rays off a surface. This depends on the angle at which it
strikes the surface. A ray striking a mirror perpendicularly is reflected 180˚ back upon
itself and a ray striking a mirror at 45˚ angle is reflected 90˚.
Absorption: the transfer of light energy to a particle or surface. Black surfaces absorb the
energy of all visible wavelengths. Some absorb light energy only in a limited range of
wavelengths and reflect the remaining wavelengths. For example, a blue pigment
absorbs long wavelengths but reflects a range of short wavelengths centered on 430 nm
that are perceived as blue.
Refraction: the bending of light rays that occur when they travel from one transparent
medium to another. It occurs because the speed of light differs in two media (e.g. light
passes through air more rapidly than through water). The greater the difference between
the speeds of lights in the two media, the greater the angle of refraction. (see Fig. 9.3).
THE STRUCTURE OF THE EYE
Gross Anatomy of the Eye
Pupil: the opening that allows light to enter the eye and reach the retina. It appears dark
due to the light-absorbing pigments in the retina.