Artemide Dictionary of Light
Halogen source
Lamp containing a tungsten filament and a small
amount of one or more halogen gases for the
purposes of cyclic regeneration of the filament.
Hybrid optic
Optical system in which both mirrors and
lenses are used. More generally, both reflective
and refractive elements are employed.
Illuminance uniformity factor
(on a given plane)
Measurement of the variation of illuminance
on the plane concerned, expressed as:
ratio between the minimum and maximum
illuminance; ratio between the minimum
and average illuminance.
Illumination
Photometric value showing the quantity of luminous
flux for surface area. Common measurement units
are lux (lumen / m2) used in the international system,
and foot-candle (lumen/ft2) in the United States.
Localised illumination
Illumination designed to light an area with
greater brightness in specific positions, such
as where a very accurate visual task is being
carried ou.
Incandescent source
Lamp in which the light is produced using
an element brought to incandescence
by the passage of electric current, which emits
radiation in the visible range.
Infrared radiation
Optical radiation having a wavelength greater
than those of visible radiation.
Insulating class
homogeneous grouping defined by the IEC
(International Electrotechnical Commission),
indicating the technical features applicable to an
electric device in order to reduce electrical hazards
in case of fault. Class I electrical devices: the pro-
tection is based on the mains insulation and
on a additional security measures. This is made
by the connection of the conducting parts accessi-
ble to a protection conductor (protection earthing/
grounding system) falling under the fixed electrical
system. Class II electrical devices: also known
as double insulation devices, are manufactured
so that the earthing/grounding system is not
required. In this case an eventual fault cannot
cause the user to come into contact with
dangerous electrical tensions. Class III electrical
devices: the protection against electrocution
is due to the use of SELV (Safety Extra-Low
Voltage) security tension. The device is operated
either by a battery or by a SELV transformer.
International System of Units
Abbreviated to “SI system” or sometimes just
“SI”, this is the set of units of measure agreed
on by all countries that have signed the Metre
Convention.
IP
International Protection (or protection class IP)
is a code summing up the level of protection
of an electrical appliance in case of accidental or
intentional contact with a human body or with
objects, and also the protection against contact
with water. IPXX: the first digit shows the
protection against the contact with solid bodies
and the contact with dangerous parts.
The second digit shows the protection against
the contact with liquids.
Iso-illuminance curve, isolux curve
Locus of points belonging to a surface at which
the light intensity has the same value.
Kelvin
The kelvin (K) is a unit of measurement
of temperature that is one of the seven base
units of the International System of Units.
In lighting, it is the measurement of the colour
of light. See colour temperature.
Lambert surface
Ideal surface that reflects the energy coming
from one direction equally in all directions,
and thus its luminance remains the same even
if the viewpoint is different. It is therefore
an ideal diffusing surface.
LED
Acronym of Light Emitting Diode. The LED
is an electronic device made by the union
of two elements composed of semiconductor
material (typically silicon). The two elements
are “doped”, meaning that specific materials
are added to them so that one has mainly
negative charges (electrons) and the other one
has mainly positive charges (holes). The passage
of electrical current through the “junction”
of the two elements causes the electron-hole
recombination to occur, and this produces the
phenomenon of the spontaneous emission
of light at a given wavelength.
The LED is therefore a monochromatic light
emitter; white LEDs are blue LEDs which,
through their radiation, excite phosphors which
in turn, according to the same phenomenon of
spontaneous emission, convert part of the blue
radiation into others of the visible spectrum.
Lens
Optical element producing convergence
or divergence of light rays on itself, thanks
to refraction.
Life cycle
See Service Life.
Light
Portion of electromagnetic waves spectrum
that are visible to the human eye.
Light guide
Transparent optical element transporting light
by means of TIR effect, e.g. optic fibre.
LOR (Efficiency)
Acronym for Light Output Ratio.
It is a percentage value obtained by the ratio
between the luminous flux of a device
and the luminous flux installed.
Louvre screen
Screen whose shielding elements are lamellae
made of opaque or translucent material.
Lumen
SI unit of luminous flux. The lumen (lm)
is the luminous flux emitted in a unit solid angle
by a uniform point source having a luminous
intensity of 1 candela.
Luminaire
Generic term to indicate a lighting device.
Luminance
Photometric valuee showing the luminous
power of a light source for solid angle unit and
for surface unit. It is used to define how bright
a surface is at a certain angle. In the Internatio-
nal System it is measured in candles per square
metre (cd/m2), in the United States
in foot-lambert.
Luminous flux
Photometric value showing the amount of light
emitted by a light source. It comes from the
radiant flux (W) and is expressed in lumen.
Luminous intensity
photometric value expressing the lighting power
of a source for solid angle unit. It is an essential
value in the International System; it is used to
define how bright a specific point is at a certain
angle. It is measured in candles (cd).
Lux (lx)
SI unit of illuminance. Illumination produced
on a surface with an area of 1 square metre
by a luminous flux of 1 lumen uniformly
distributed on this surface.
LV (Low Voltage)
Components (electrified plates, optional
extensions, cables and feeding kits) with 3-wire
cables (+, -, signal) and 48VDC feeding tension.
Feeding unit and control interfaces are needed
in addition. Generally used for RGB LEDs,
with the exception of Stand Alone versions.
MacAdam Ellipse
In CIE chromatic diagrams, these are elliptical
areas defining the ability of the human eye in
perceiving colour differences from the centre
of the elliptical area. E.g., a Step3 MacAdam
Ellipse means that on average the human eye
is able to perceive 3 different colours from the
centre to the border of the ellipse.
Mean daylight factor
Ratio, expressed as a percentage, between
the average illuminance of the room and the
illumination under the same time conditions
on an external horizontal surface that receives
light from the sky.
H
I
K
M
L
12
