Artemide Dictionary of Light
Radiation
Emission or transportation of energy in the form
of electromagnetic waves or particles.
Radiometry
From latin RADIUS (ray) and greek METRIA
(measurement). Branch of physics studying
measurement of radiometric magnitudes related
to electromagnetic energy, such as radiating
flux (W), radiating intensity (W*sr-1), radiation
(W*m-2), radiance (W*sr-1*m-2).
Reflection
Physical phenomenon that occurs when a ray
of light projects onto a mirror surface. The angle
between the incident ray and the perpendicular
to the incident point are equal to the angle
between the reflected ray and the perpendicular
to the incident point.
Reflectance
Ratio between the luminuous flux reflected
by a surface and the luminous flux incident
on the surface.
Reflective Screen
Screen in which the shielding depends
mainly on the phenomenon of refraction.
Reflector
Optic element able to reflect light. This term
includes all elements treated with vacuum-
sealed aluminium and producing a specular
surface. It is a fact though that also all opaque
elements are to some extent reflectors.
Refraction
physical phenomenon that occurs when a ray
of light projects onto a border between two
mediums with a different refraction index (or
with two different densities). The refraction law,
also known as Snell law, is defined as follows:
n*sen(i) = n’*sen(i’). n and n’ are refraction
indexes of the first and second medium; “i” and
“ i ‘ “ are the angles relative to the perpendi-
cular of, respectively, the incident ray and the
refracted ray.
Remote Control
Infrared remote control for light management.
Retrofit
Light source using an advanced technology
replacing an obsolete one with the same
mechanical features.
Retroreflector
Optical device designed to deflect the rays
that fall on it towards the source of the light.
The rays undergo two refractions and
a reflection in variously shaped elements.
RGB
Acronym for RED – GREEN – BLUE, used
to identify systems with multi-coloured light
sources which, through additive synthesis, can
create all the colours of the visible range and
their possible combinations, including white.
Spectrum
Distribution of a radiometric magnitude
(radiance, radiation intensity, radiating flux),
as a function of radiations frequency
or wave length.
Standard EN60598-1
Standard regarding electrical safety of lighting
devices.
Standard IEC/EN 62471
Standard regulating photo biological perspective
of the usage of LED sources.
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.
TCO (Total Cost 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).
ϑ (Theta)
Theta - In a photometric solid with rotational
or X-Y symmetry, the angle between
the intensity 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.
ϑ/2 (Theta ½)
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 ϑ/½ (2 Theta ½)
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.
Rods
Photoreceptors of the retina in which
pigments are sensitive to scotopic vision.
Rods are considered not to play any role
in the discrimination of colour stimuli.
Security lighting
Part of the emergency lighting system designed
to ensure the safety of persons.
Saturation
Attribute of a visual sensation that allows you
to judge the proportion of pure chromatic
colour in the total sensation.
Scotopic vision
Vision that occurs when the eye adapts
to luminance levels less than a few hundredths
of a candela per square metre; the rods
are considered the main active components
of the eye in this condition. The spectrum
appears not coloured.
Screen
Part of a lighting device consisting of translucent
or opaque elements, geometrically arranged
in such a way as to hide the lights from the
observer at certain angles.
Secondary optics
In an optical system, these are elements
that are intercepted by light in the second place.
LED power supplies are created especially for
the piloting of LED load. There are two main
groups: the constant current power supplies
regulate directly the current of the LED load,
while the constant tension power supplies
create a continuous tension through which
other devices controlling LED loads can be
operated.
Sensitivity
Quotient between the response Y
of a detector and its excitation X.
Service Life
Time period from the first time a light source
is switched on and a specific percentage of its
estimated life span (e.g. 70%). LED manu-
facturers estimate the life cycle through tests
lasting less than its determined life span. E.g L70
(6K)>36,000 hours means that the light source
will produce a luminous flux higher than 70%
of its initial luminous flux after 36,000 hours.
Also, this estimate was performed through a
test of 6,000 hours.
Solid angle
Solid angle subtended at the centre
of a sphere by a cap with an area that is
numerically equal to the square of the radius.
Measured in steradian, sr.
Source
Any element able to product an electromagnetic
radiation.
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