Electric Lamp, Lighting, Bulbs and Tubes part 1

The amount of light given out or produced by an electric lamp — bulb, striplight or fluorescent tube — depends on the type of lamp and its wattage. The light produced is measured in lumens and a bulb or tube of a given wattage produces an average output of so many lumens. This will continue throughout most of its life.

Equally important is the number of lumens produced for each watt consumed, so it is usual to say, when comparing types, that a bulb or tube produces so many lumens per watt. The more the lumens per watt, the higher the efficiency of the lamp.

Comparison of Lamp Efficiencies

The electric light bulb operates at a fairly low efficiency whereas the fluorescent tube operates at a much higher efficiency at least three times that of the bulb. It is because of the inherent low efficiency of the bulb that there has been so much scope for improvement.

The efficiency of an electric light bulb is in the region of 25 %; the remainder of the power consumed being emitted in heat. A bulb is really an illuminous heater and is often used as such. On the other hand, a fluorescent tube is cool in comparison; though the coolness of the glass is partly due to the fact that there is more glass in a bulb of given wattage and the heat is distributed over a wider surface area.

The luminous output of a fluorescent tube also varies with its ‘colour’; the ‘white’ tube having a light output double that of the ‘artificial daylight’ tube for the same watts consumption. However, provided a

Tube of a given wattage produces sufficient light of the right colour in a room, variation in lumens output of the different colours is of little concern. This is not so with bulbs, where you may need to have one of higher wattage to get adequate light for the purpose, and therefore consume more electricity.

Types of Electric Light Bulb

The ordinary electric light bulb is made in two principal types and in a wide range of wattages. The two types are single-coil and coiled-coil. The coiled-coil produces more light than a single-coil for a given wattage. Where possible it is therefore wise to choose a coiled-coil type.

Single-coil bulbs

These are made in about a dozen sizes ranging from 15 W to 1500 W though in the home the 150 W bulb is the largest normally used. This latter is also the largest type made with a bayonet cap to enable it to fit an ordinary lampholder. Some variants are plain, pearl and pink pearl, conventional bulb shape and mushroom shape.

Coiled-coil bulbs

The coiled-coil type is limited to five wattages: 40 W, 60 W, 75 W, 100 W and 150 W, and is available in plain and pearl versions for all four sizes. It is not made in mushroom shape nor in pink pearl ‘colour’. If, therefore, you require sizes other than those listed above you must buy single-coil lamps.

Coloured Bulbs

Coloured bulbs of conventional size and shape are made in the colours: amber, blue green, pink, white, yellow and red, and in 15 W, 25 W, 40 W, 60 W, 100 VV and 150W sizes. The 15 W and 25 W types are suitable for outdoor use, but other sizes must be enclosed for protection against the rain. Most, but not all the colours, are available in the larger wattages.

Round bulbs of 15 W and 25 W, in various colours, are available for festive purposes together with other shapes.

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