Steradian (sr)
SI unit derived from a solid angle which, having its vertex in the centre of a sphere,
cuts an area of the spherical surface equal to that of a square having the radius of the
sphere as its side.
T
TCO (Total Cost of Ownership)
Latest generation calculation tool used to come up with lighting and system control
solutions to ensure a targeted use of energy resources, starting from regular estimates
of the costs of installing and operating the equipment.
Tension
Difference between the electric potential between two points in space, caused by
their electrical power.
Thermal management
Management of the thermic dissipation of a light fitting, usually LED.
Thermal radiation
Emission process in which the radiant energy has its origin in the thermal agitation of
the particles making up the matter (atoms, molecules, ions).
Theta
In a photometric solid with rotational or X-Y symmetry, the angle between the inten-
sity vector with half the maximum value of the solid and a second intensity vector also
with half the maximum value, but whose position is a mirror image of the first vector.
(½ Theta)
In a photometric solid with rotational symmetry or XY symmetry, the angle between
the maximum intensity vector of the solid and a second intensity vector with half the
maximum value.
(2 ½ Theta)
In a device with rotational or X-Y symmetry, twice the angle between the maximum
intensity and the intensity equal to half of the maximum.
TIR lens
Optical element that, associated with an LED, works as a parabolic reflector using
the total reflection principle. This happens when the light hits a border between
two optical mediums, one firmer and one softer. TIR is the acronym for Total Internal
Reflection.
