age loss is greater, more heat is developed,
and lamp efficacy is lower.
Neonis a particular kind of small-diame-
ter, cold-cathode lamp; it is easily bent to
form signs and artworks. The operating prin-
ciple is related to that of other cold-cathode
lamps, but light is produced by excitation of
the gas itself without the help of phosphors.
All cold-cathode lamps provide instant start-
ing and are easily dimmed.
Although lower in efficacy and output,
cold-cathode lamps have a longer life. They
are used for decorative applications and in
places where inaccessibility makes lamp
replacement difficult. Cold-cathode lamps
are less frequently used than the hot-cath-
ode kind.Hot-Cathode
Hot-cathodelamps are used for virtually all flu-
orescent lighting. The cathode is a coiled tung-
sten filament at each end of the bulb
impregnated with electron-emissive materials.
Hot-cathode lamps are operated at a higher
light output per unit length and with a higher
overall efficacy than cold-cathode lamps,
resulting in a lower cost for equal illuminance.INTERIOR LIGHTING FOR DESIGNERS
Figure 7.1The fluorescent (hot-cathode) lamp consists of a glass tube, internally coated with phosphors that convert
ultraviolet energy into light; cathodes supported by a glass structure and sealed at the ends of the tube; a filling gas to aid
starting and operation—usually a combination of krypton, argon, and neon; a small amount of mercury, which vaporizes
during lamp operation; and a base cemented on each end of the tube to connect the lamp to the lighting circuit.
Figure 7.2Cold-cathode lamp.