No lamp, no light. The term "lamp" refers to an engineered artificial light source, e.g. incandescent lamp, energy-saving lamp, compact fluorescent lamp. Lamps are used in luminaires, which distribute and direct the lamps' light and prevent it causing glare.

Luminance (symbol: L) is the brightness of a luminous or illuminated surface as perceived by the human eye. It is measured in candelas per unit area (cd/m2). For lamps, the more convenient unit of measurement cd/cm2 is normally used.

The term "luminaire" refers to the entire electric light fitting, including lamp. Luminaires protect lamps, distribute their light and prevent it causing glare.

Luminaires are differentiated

on the basis of type lamp (incandescent, fluorescent, discharge lamps),

number of lamps (single-lamp, twin-lamp, etc.)

intended location (interior luminaires, exterior luminaires),

degree of protection (luminaires for dry, damp and dusty interiors),

type of construction (open luminaires, enclosed luminaires, reflector luminaires, specular reflector luminaires, louvered luminaires, diffuser luminaires, floodlights)

and application (technical luminaries, decorative luminaires).

Luminous efficacy is the measure of a lamp' efficiency. It indicates how many lumens (lm) per watt a lamp generates. The higher the ratio of lumens to watts, the more light a lamp produces from the electricity it consumes.

Light colour describes the colour appearance of a lamp's light. Light colours are based on colour temperature expressed in degrees Kelvin (K):

warm white (ww) < 3,300 K
neutral white (nw) 3,300 K to 5,000 K
daylight white (dw) > 5,000 K

The luminous flux defines the quantity of light emitted from a light source in the visible spectrum. The luminous efficiency is the ratio of the luminous flux to the electrical power consumed (IM/W). It is a measure of a lamp’s economic efficiency.

The lighting quality of artificial lighting is indicated by lighting quality features. Each one relates to a specific lighting requirement:

lighting level determines brightness

glare limitation makes for vision free of interference by direct or reflected glare

harmonious brightness distribution ensures an even balance of luminaince

light colour defines the colour appearance of lamps, and in combination with

colour rendering makes for correct recognition and differentiation of colours and defines room ambience

direction of light and modelling determine how well we recognise surface colours and structures.

These are luminaires with a louver enclosure, mostly designed for use with tubular fluorescent lamps or compact fluorescent lamps. Louvers are optical controllers: they define the intensity distribution of the luminaire and at the same time prevent glare.

Lighting engineers often refer to their area of expertise as the "science of lux and lumen". The two terms are units of measurement for key lighting variables.

Lux (lx) is the unit of measurement of illuminance. It indicates how much light – or more specifically how much luminous flux – falls on a given surface. Measurements are performed with a luxmeter. In an office, for example, at least 500 lux is required for desk work.

Luminous flux is measured in lumens (lm) and describes the visible light radiating from a lamp in all directions. Two examples: an incandescent lamp has 1,400 lumens, a double-based halogen lamp as many as 44,000 lumens. The luminous flux ratings of lamps are found in manufacturers' product lists.