ABSTRACT
The earth’s atmosphere is thick with electromagnetic radiation, emitted by sources such as stars, mobile phones, people and buildings. The lighting requirement will vary according to the function of a space and the tasks carried out within it. Four key criteria for achieving good lighting conditions are: illuminance, modelling, colour rendering and visual contrast of surfaces. Luminous intensity is power of visible light emitted for a solid angle of one steradian. An accurate description of colour has three components: the colour of the light emitted by sources; the colour of the incident surface; and the ‘rendering’ of colour. Human interaction with light is complex, encompassing physical health, vision and physiology, as well as less measurable effects on mood and emotions. Ultraviolet light has higher energy levels than visible light and affects the skin and eyes. A type of photoreceptor, ganglion cells, send signals of light and dark directly to hypothalamus, the part of the brain that regulates many physiological functions.
