Facilities: Lighting - Energy Conversion and Management - page 236

Chromaticity or color temperature is an index of the light color that includes
consideration of its dominant wavelength and purity. It is expressed in Kelvin
temperature. The higher the temperature, the cooler the light (typical reference
values are 4,100 K for the moon; 5,000 K for the sun; 10,000-25,000 K for blue
sky). Chromaticity is defined as the temperature of a black body radiating light
with the same color as the light source.
Color rendering or color rendition is an index of the effect of a light source on the
color appearance of objects compared with color appearance under a reference
light source (the value of color rendering for the reference light source equals 100).
Space distribution diagrams take into account that light emitted from a lamp or a
luminaire may vary in luminous intensity depending on the direction. Diagrams
are generally made on a plane section and report candle values referred to a flux
of 1,000 lm to allow comparison among different lighting systems.
Luminaire ( or fixture ) is defined as a complete lighting unit consisting of a lamp or
lamps and components designed to distribute the light (diffuser, reflector, lens,
and others) and to connect the lamp to the power supply.
Coefficient of utilization ( CU ) or luminaire efficiency is the ratio of the luminous
flux (lumen) reaching the working plane to the total flux (lumen) generated by
the lamp. This coefficient takes into account light absorbed or reflected by walls,
ceilings, and luminaries. Its values are generally found in charts in the
manufacturer's catalogue and permit a quick estimation of the lighting that
can be achieved with a given system.
Lamp and luminaire depreciation factor relates the initial illumination provided by
a clean, new lamp and luminaire to the reduced illumination that they will
provide at a particular point in time because of accumulated dirt and deprecia-
tion (see Fig. 14.1 ).
Task surface is the working area where the recommended levels of illumination
specified by international associations should be applied. For the surrounding
area the level of illuminance should be no more than 1/3 of the average level of
the task surface. Table 14.1 shows typical values of illuminance for different
industrial task surfaces; it ranges from 2,000 lx for high-precision operations to
50 lx for transit areas.

14.3 Typical Lighting Systems and Related Equipment

A lighting system may have many components: ballast, dimmer, lamp, diffuser,
reflector, lens, and control equipment.
Systems are generally classified according to lamp categories, as follows:
incandescent, fluorescent, high-intensity discharge such as mercury vapor, metal
halide vapor, sodium vapor (high pressure and low pressure), and LED (light-
emitting diode).
For all lamps, except for the incandescent lamps, the power factor is generally
less than 0.5; to improve this value, capacitors must be provided (see Sect. 7.3 ).
Tables 14.2 , 14.3 , 14.4 , and 14.5 show the typical values of the main parameters.