i) Lamp efficiency or luminous efficiency: It is the ratio of luminous flux emitted by a lamp to the power consumed by the lamp. It is a reflection of efficiency of energy conservation from electricity to light form. Unit is „lumen / watt‟.
ii) Luminous flux : It is the rate of flow of luminous energy and measured in terms of „lumen‟
iii) Luminaire: It is a device that distributes or transmits light emitted by one or more lamps. It includes all parts necessary for fixing and protecting the lamps, circuit‟s auxiliaries for connecting to supply. It works based on principle of reflection, absorption, transmission and refraction.
iv) Colour Rendering Index (CRI): It is a measure of the degree to which the colours of surfaces illuminated by a given source compare to those of the same surface under reference illuminant.