Electric Lamp, Lighting, Bulbs and Tubes part 3

Quick start Tubes

Some fluorescent fittings have no starter switch(s) for the tubes. Instead there is S transformer to provide the prewarming and the tube itself has a metal stripe running throughout its length from one lamp cap to the other. The lamp caps are earthed at the lampholders.

This assists in the starting of the electron flow and, as there is no starter to operate, the lamp strikes without the characteristic delay of the switch-start type.

Tube life

A fluorescent tube has an expected life of 5000 to 7000 light hours or up to seven times that of an electric light bulb.The actual life of a tube is shortened by frequent switching on and off because each time the tube is switched on some of the coating on the electrodes is eroded, but with such a long life — about ten years — with average use any shortening of the life of a tube is hardly noticed.

A quick-start tube on a starterless circuit has a shorter life than a switch-start tube because more active material is eroded from the electrodes, but the life is still in the 7000-hour region.

Choosing the correct tube

The length of tube chosen depends to a large extent on the fitting chosen. The 4 ft 40 W type in either single- or double-tube version is a useful size for the kitchen. One 40 W tube gives a light output in excess of that from a 100 W bulb and with less than half the electricity consumption.

For reception rooms, hall, bathroom and other areas the smaller tubes are usually adequate and preference is often shown for the circular tube contained in an attractive fitting. For pelmet lighting, and other lighting where the tubes are hidden, the 5 ft 65 W or 80 W tube should be considered. For a long pelmet the 8 ft 125 W tube may be the better choice.

In the garage one or more 5 ft 80 W tubes of a high light output ‘colour‘ will give the best light for car repairs. Mini-tubes are suitable as strip lights but usually come with the fittings, for example a shaving mirror light.

Colour range of fluorescent tubes

Fluorescent tubes are available in an extensive range of ‘colours’ but only a few of these are acceptable in the home for which warmer colours are recommended. Colour rendering is also important so that the colours of objects and materials are not too distorted. The most popularcolour is de-luxe Warm White and this is chosen for living rooms in conjunction with filament lamps.

Where maximum light output is required, such as in a kitchen, White or Warm White should be chosen but with the sacrifice of some colour rendering. There is also available a colour which is used where a warmer colour than from filament lamps is required. These are sold under various trade names and, in addition to giving a warm colour, have good colour rendering qualities.

For decorative lighting giving a very warm effect, you can choose a pink tube and accept its poor colour rendering. For the garage you can have White or Warm White but where accurate colour matching may be required you should choose Artificial Daylight, or Daylight, to blend with natural daylight.

Circular tubes are made in Warm White only. This is generally considered to be the best all round colour for the home.

Fluorescent lighting circuits

The fluorescent fitting is connected to the same wiring as any other lighting fitting except that an earth is essential with the starter-less type. Modern lighting circuits have an earth conductor at each lighting point. An earth conductor should also be installed at every lighting point where the fitting is of metal. Where there is no earth at a point it is necessary to run a 1.5 mm²green insulated cable from the point to the earthing terminal at the consumer unit.

The internal wiring of the fluorescent fitting depends on the type of tube and whether it has one or two tubes. The three principal circuits are: switch-start circuits; quick-start circuits and twin-tube circuits.

Switches for fluorescent lighting

The normal wall switch one-way on/off and two-way are used with fluorescent lights but, because of the surge on starting, the switch must be capable of handling the current, otherwise the contacts of the switch will burn out.

The standard plate switch of good quality available from all leading makes is adequate for fluorescent lighting. There should be no problem except, possibly, with low quality switches.

Fluorescent tube faults and remedies

Unlike a bulb which burns out completely at the end of its useful life a fluorescent tube lingers on and behaves in a strange, though characteristic; manner. A new tube sometimes behaves similarly when first switched on but this ceases after a while.

A faulty starter, or other faults in the fitting, also cause a tube to behave strangely.

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