In 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
A 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.
Metal 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
High 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.
Mercury 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
Incandescent 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.