Lamps and lighting: light sources and fittings explained
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Lamps are either light fittings or the bulbs inside them, and the bulb decides most of the running cost. The US Department of Energy compares the options: an incandescent bulb loses 90% of its energy as heat, while an LED uses at least 75% less energy and lasts 25 times longer.
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Two meanings of lamp
In everyday English a lamp is a device that gives artificial light — dictionary.com’s first sense — and in British usage, as the Collins entry on the same page puts it, a device holding one or more electric bulbs, such as a table lamp. In the lighting trade the word also means the light source itself — the bulb or tube — and the UK HSE’s lighting guide uses it that way. Both meanings meet on the shelf, so a lamp light for sale may be a whole fitting or just the bulb that goes in it.
Lighting a house means choosing both: the fitting decides where light goes, the lamp inside decides how much light, of what colour and at what cost.
Light sources compared
The US Department of Energy’s Guide to Energy-Efficient Lighting sets the main household light sources side by side:
| Light source | Energy and heat | Life | Note from the source |
|---|---|---|---|
| Incandescent (filament) | wastes 90% of its energy as heat | the baseline | old technology, per the DOE |
| Compact fluorescent (CFL) | 75% less energy and 75% less heat than incandescent | up to 10 times longer | contains a small amount of mercury, so it should be recycled |
| LED | at least 75% less energy; virtually no heat | 25 times longer than incandescent, up to 4 times longer than a CFL | dimmable; cool to the touch |
| Tungsten halogen | runs at high temperature | — | the UK HSE warns of ultraviolet output at close range in desk lamps and spotlights |
The figures are the ones the DOE published in October 2010.
Lamps by where they go
Lights and lamps are named by where they sit and what they light:
- Table and floor lamps — free-standing, plugged in, for reading and working light; see table lamps.
- Wall lights — fixed to a wall, beside a bed, mirror or doorway; see wall lights.
- Ceiling lights — flush, pendant or recessed fittings that light a whole room; see ceiling lights.
- Outdoor fittings — bulkheads, lanterns and floodlights sealed against water and dust.
- Emergency lamps — battery fittings that switch on by themselves when the mains fails; see emergency lamps.
Reading a fitting’s label
A fitting’s label tells you which lamp it takes and where it can go. The bulkhead lights in Legrand’s Tanzania lighting catalogue are a clear example, each described by a short string of codes:
| Legrand bulkhead | IP | IK | Lamp |
|---|---|---|---|
| oval, plastic grid | IP 44 | IK 06 | E27, 60 W |
| round, glass or polycarbonate diffuser | IP 44 | IK 07 | E27 |
| oval or round, for tough environments | IP 55 | IK 04 | E27, 75 W or 100 W |
| Plexo, rectangular | IP 54 | IK 08 | 55 W incandescent |
Read left to right: the IP code rates the seal against dust and water, the IK code rates resistance to knocks (the higher the number, the harder the blow), and the last column gives the cap and the most powerful lamp the fitting is built to take. Fitting a lower-wattage LED lamp with the same cap keeps well inside that limit.