I
Illumination
Photometric value showing the quantity of luminous flux for surface area. Com-
mon measurement units are lux (lumen / m2) used in the international system, and
foot-candle (lumen/ft2) in the United States.
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 Commis-
sion), indicating the technical features applicable to an electric device in order to
reduce electrical hazards in case of fault.
Class I electrical devices: the protection is based on the mains insulation and on a
additional security measures. This is made by the connection of the conducting parts
accessible 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.
