ABSTRACT
Natural lighting has important implications for site layout and massing, and for energy conservation. Sunlight is increasingly important; solar geometry is the key to harnessing sunlight. The potential of sunlight, direct and diffused, in saving electrical energy by reducing the demand for artificial lighting, is less obvious. The skylight illumination reaching any point depends largely on how much sky is visible from the point in question. The constant ratio of indoor to unobstructed outdoor illuminance is usually expressed as a percentage, and is referred to as the daylight factor. The light output ratio (LOR) of a luminaire is the proportion of luminous flux from the lamps which emerges from the luminaire. Electric lighting is switched off automatically at a control panel at the same time each day, perhaps to coincide with work breaks, e.g. at midday. The sizing of overall lighting installations for working interiors and for floodlighting is nowadays left to computers.
