order to see Colour you need a light that contains that colour. Some
light sources are good with brown and red colours (low colour
temperature) and some are better to emphasize blue and green colours
(high colour temperatures).
Light tubes produce light when a starter
generates an electrical pulse, which starts a discharge of gas in the
tube. This discharge generates ultraviolet light that is transformed
into visible light when it meets the fl uorescent coating (light powder)
in the tubes glass wall. Different light powders dictate the spectral
characteristics. A current through the tube limits/increases the
discharge process and so defines the luminous efficacy.
Compact light tubes
compact light tube is in reality just an ordinary tube that has been
bent around on itself so you only need one lamp per fi tting. There are
two principle types. One has built-in starter (2 pin) and the other does
not (4 pin). Note that for HF ballast or integrated emergency lighting
you should always use 4 pin compact tubes as the HF ballast and
emergency light units have their own ”starter” built in.
halide lights produce light by starting an electrical discharge in
argon gas between primary and secondary electrodes. This causes
ionisation in the discharge tube so the discharge between the electrodes
starts. This requires a high starting voltage. For this reason an
external starter is used that gives start pulses of 1.5 – 4 kV. It can
take up to 10 min. before the light has reached full light flux. Ceramic
versions give more stable colour temperatures and color rendering
throughout their lifetime.
High intensity sodium
intensity sodium lamps do not require secondary electrodes. The Xenon
gas is ionised with the help of an external starting ignitor that also
starts the discharge of sodium vapour. Beyond this starting the
operation is as with metal halide lamps.
lamps produce light by starting an electrical discharge in argon gas
between primary and secondary electrodes. This causes ionisation in the
discharge tube so that the discharge between the electrodes starts. It
can take about 10 min. before the light has reached full light flux.
Incandescent halogen lamps
halogen lamps work in exactly the same way as ordinary incandescent
lamps. The difference lies in the fact that a halogen is added, which
prevents the vaporised tungsten from settling on the bulb and blackening
it, but instead returns to the electrode. Since the problem of
blackening is eliminated, smaller glass bulbs can be used which are
stronger. This means that pressure is raised in the lamp. Increased
pressure produces less vaporisation of the filament and so an even
higher temperature is possible. The result is a significantly higher
luminous efficacy compared to conventional incandescent lamps.