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Dictionary
Harmonic Currents: these are multiple frequency sinusoidal waves created by an electronic power supply connected to the electrical grid (e.g. such as the one contained in a compact energy saving lamp). These “harmonics” have a negative effect on the form of the sinusoidal wave of the electrical grid voltage and disturb the other appliances connected to the same.

Candela: this is the unit of measurement of luminous intensity, its abbreviation is cd.

Colour Rendering: the colour rendering of a light source is the way in which the same renders the appearance of the colour of an object compared to that generated by a reference light source.

Color temperature: This is the term used to quantify the light tonality generated by a light source and is measured in Kelvin degrees, The reason it is called ‘temperature’ is because it derives from the measurement of the degrees of heat necessary to warm up a theoretical black body, called a radiator: as the temperature rises, the black radiator changes color, first becoming red, then yellow, etc.

Correlated Color temperature: this is the relationship between the perceived color of the light and the color temperature as described under ‘Color temperature’. Basically, only filament light sources have exactly the same luminous emission of the ideal black body: the light color of all other types of sources is defined by ‘correlation’ and is always given in Kelvin degrees, K. 

Declared Lumen: in the case of fluorescent lamps, this is the quantity of luminous emission measured after 100 hours of operation (period during which the flux undergoes a strong initial drop and then stabilizes).

Flux deterioration: a process caused by lamp aging. Each type of lamp follows the curve of luminous flux deterioration typical of its typology but this can be drastically worsened by external influences: e.g. repeated switching on and off.

Illumination: this is a graduated quantity which provides a measurement for the luminous flux intercepted by a surface and, thus, the amount of light influencing the same. The unit of measurement is the lux, which corresponds to the flux of a lumen received from a surface of one square meter.

Lifetime: this is an average calculated by laboratory tests. A certain number of lamps are switched on and powered at nominal voltage: the lifetime stated refers to the time between when the lamps were switched on and when one half plus 1 of the lamps tested went off (e.g. the 51st lamp out of 100).

Lumen: the lumen is the unit of luminous power derived from Watts through the spectral sensitivity curve of the human eye in daylight vision conditions (photopic), i.e. the electromagnetic power present in a visible band, weighted through the sensitivity of the human eye. Two lamps with an equal lumen can appear completely different. This is due to the colour temperature: the higher the temperature, the more ‘luminous’ the lamp will appear, even where the same flux is emitted.

Luminous efficiency: this is the ratio between the flux emitted and the power absorbed: Lm/W. Incandescent lamps are not very efficient since most of the energy absorbed ends up as heat. Energy saving lamps get their name from the fact that they have a high Lumen/Watt ratio.

Luminous Flux: The luminous flux  is an energetic flow weighted with the spectral sensitivity of the eye. It is measured in lumens and represents the total quantity of light emitted by a source .

Luminous intensity: this represents the luminous flux emitted in a certain solid angle. The unit of measurement is the candela (cd).

Photometry and radiometry: both of these measure electromagnetic radiation but photometry measures the radiant power that falls within the visible spectrum i.e. between 380 and 780 nm, weighting it according to the sensitivity curve of the human eye. Radiometry measures the electromagnetic radiation emitted throughout the ultraviolet spectrum, visible and infrared.

Ra: the Colour Rendering Index refers to the level of colour rendering: incandescent lamps have a rendition of Ra = 100 since they have the broadest spectrum which can render all the colours. Duralamp’s triphosphor tubes have a rendition of over Ra 85.
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