... about light, we normally mean light waves or light rays. Light intensity and light wavelength are two physical dimensions of light waves and our sensations of light depend on them. Light intensity determines the brightness of light through the energy level contained by light, whereas light wavelength determines the colour (hue) that we sense. The visible spectrum of the light is from the wavelength of about 400 nanometres to about 700 nanometres. Figure 1. The electromagnetic spectrum, which encompasses the visible region of light, extends from gamma rays with wave lengths of one hundredth of a nanometer to radio waves with wave lengths of one meter or greater (ACEPT W Group, Department of Physics and Astronomy, Arizona State University, 1999). For instance, at a given intensity, different wavelengths produce sensations of different colours (e.g.: blue, red, or yellow), whilst at a given wavelength, different shades of a colour result from different ...

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