Illuminance (symbol: E, unit: lux) indicates how much light – more specifically how much luminous flux (in lumens) – from a light source falls on a given surface. Where an area of one square metre is uniformly illuminated by one lumen of luminous flux, illuminance is one lux. For example, an ordinary candle flame generates around one lux of illuminance at a distance of one metre.

Illuminance is measured on horizontal and vertical surfaces using a luxmeter. However, it is not a precise measure of the brightness of a room, which depends crucially on the reflectance of the room surfaces. Under the same lighting, a white room appears brighter than a room with darker surfaces. See also semi-cylindrical illuminance.

Indirect lighting

Indirect lighting is where light from luminaires is directed only onto ceilings or walls and is reflected by them into the room. Lamps are screened from view and light emission above eye level prevents glare. Indirect lighting is generally used in combination with direct lighting since on its own it can create a monotonous atmosphere with shadows too pale for good modelling. Where indirect lighting is used, the reflectance of ceiling, walls and floor should not be too low; in many cases, this would make it an impractical lighting option for reasons of energy efficiency.

Injection blow moulding

A blow moulding process in which a parison is formed over a mandrel by injection moulding and blown to its final form and dimensions in a second mould.

Injection moulding

A process of moulding a material by injection under pressure from a heated cylinder through a sprue (runner, gate) into the cavity of a closed mould where it cools and solidifys.

Intensity distribution

Intensity distribution describes the way luminous intensity is distributed in the room. Shape and symmetry of intensity distribution indicate whether a luminaire (or reflector lamp) casts a narrow or wide-angled beam and/or provides symmetrical or asymmetrical lighting. Intensity distribution is indicated by IDCs, intensity distribution curves on a graph. These are formed by joining the points on a polar diagram showing the luminous intensity generated at different angles by a luminaire (or reflector lamp).