Transformer
Electrical device used to transform input and output electrical power parameters
(tension, current intensity), maintaining constant electrical power.
The transformer is a device that can be operated in alternate current, thanks to the
electromagnetic principles linked to variable fluxes.
Tunablewhite
Light source able to create different tones of white light, going from warm (2,500K) to
cold white (6,500K). It can be made of white or coloured sources.
U
UGR
Unigied Glare Ratio. Parameter expressing the glare of a light fitting, through the
evaluation of its luminance.
Ultraviolet radiation
Optical radiation with wavelengths shorter than those of visible radiation. In the range
between 100 and 400 nm, ultraviolet radiation is generally indicated with the symbols
UVA between 315 and 400 nm, UVB between 280 and 315 nm and UVC between
100 and 280 nm.
Uni EN 12464 standard
UNI standard that establishes the lighting technology parameters related to worksta-
tions. The standard defines characteristics such as: Minimum illumination, uniformity,
colour rendering of sources and UGR for various workplaces. This standard also pre-
scribes the maximum permissible luminance of a device for its use in places where
there are video terminals.
Uniformity
In a illumination (lux) or luminance (cd/m2) map, it is the ratio between the lower and
the average value observed.
V
Very Wide Flood
Term to identify a 2 ½ theta opening greater than 30° in a projector.
Visible radiation
Optical radiation that directly causes a visual sensation. Even if the range of wave-
lengths concerned in vision depends on the individual and on the illuminance on the
retina, the lower limit is normally indicated between 360 nm and 400 nm and the
upper limit between 760 nm and 830 nm.
