Table lamps

Faulty table lamps, desk lamps and floor-standing lamps, often cherished items, are usually quite easy to repair and spare parts are available. Owners are often confused, though, by the range of different types of bulb that are available.

Summary

We often see table lamps and the like at Restart Parties. Often, these are quite old - maybe the owner has had them for many years and has a personal attachment to them, or maybe they simply took a fancy to them in a second hand shop. Others are relatively new and have just stopped working. Some may have frayed wires and be positively dangerous. Whatever the history there is a good chance they can be given a new lease of life.

Safety

An electrical safety test is highly recommended, including a visual check, both before and after a repair, especially for an older item.

As with any mains operated item, it's a good idea to have the plug on the bench in front of you before starting to work, so you can be certain you didn't forget to unplug it.

Fault finding

The first and most important task is to inspect the electrics. A frayed lead, cracked plug or cracked or faulty switch must be replaced. Check the fuse with a multimeter on a low resistance range.

If the lamp uses a filament bulb, check this too with a multimeter. A faulty low energy (compact fluorescent or LED) bulb can only be positively identified by substitution.

If the lamp uses a mains voltage bulb (of whatever sort), test continuity between the plug and the bulb holder with a multimeter on a low resistance range. To do this, touch one probe on one of the pins of the plug (but not the big earth pin) and see if you can get a zero reading by touching the other probe on one of the contacts in the bulb holder. The switch may be off. Try it in the other position. Now repeat with the probe on the other pin of the plug. If you can't get a zero reading in either case then there is a break in the wire, or the switch is faulty.

Lamps using a low voltage halogen or LED bulb have a transformer or an electronic equivalent in the base. This is harder to test but you should still be able to test for continuity between the plug and the transformer and between the other side of the transformer and the bulb. Check for any signs of overheating, or for a bulging or leaking electrolytic capacitor.

Some such lamps have touch controls for on/off or for dimming. These too are harder to diagnose beyond smple continuity checks and a visual inspection for obvious faults.

Repair

A wide range of spare parts for lamps is available online, including brass or plastic lamp holders and fittings, switches and decorative or fabric-covered flex for an authentic restoration of a vintage lamp. Simply search online for "lamp parts" or "lamp fittings".

Getting inside a table lamp with a decorative base such as glazed porcelain is sometimes a little tricky. A porcelain base may have a paper and felt bottom to prevent it scratching a polished surface, and you may need to remove this to get inside. Sometimes you may have to unscrew the top. You may have to pull the lead from the plug into the base in order for it not to get impossibly twisted in the process.

The lamp holder may need replacing. This may be plastic or brass, and with or without an integral switch. Other brass fittings such as threaded tubes and nuts to fit them may also need to be replaced.

A brass lamp holder should have a screw terminal for the attachment of an earth wire. It's very important that this is connected as otherwise a fault could be lethal.

Types of bulb

Filament, florescent or LED

There are 3 kinds of bulb:

• Filament or incandescent bulbs. These contain a thin wire which glows white hot when a current passes through it. They are very inefficient and have a relatively short life. Standard "tungsten" types can no longer be legally sold.
  • Halogen bulbs are a newer type of filament bulb, somewhat more efficient and with a longer life. They contain a halogen gas which helps preserve the life of the filament (still made of tungsten) and so can be run hotter and hence more efficiently. The envelope is made of quartz so as to withstand the higher temperature rather than standard glass, often mounted inside a standard glass bulb.
  • "Vintage" or "antique" bulbs are available for decorative use, often rated at 25W, 40W or 60W. These generally have a large glass envelope and a filament in a large coil or strung between a number of supports. They give a warm amber glow. However, they are extremely energy inefficient. (Some LED filament bulbs have a very similar appearance but much lower wattage - don't be fooled.)
• Compact florescent bulbs are basically just a standard florescent tube bent into a compact shape. Both their life and their efficiency are several times greater than a filament bulb. A florescent tube cannot be connected directly to the mains but needs a ballast and a starter, and a compact florescent, instead, has an electronic circuit in its base. They tend to be bulkier than their filament equivalents and so don't always fit an existing lamp. They may take a minute or so to reach full brightness.
• LED bulbs are the newest, most expensive, but also much the most efficient type. In theory, they could be made to convert nearly all the electrical energy into light. They can be made smaller than compact florescent, so are often made in shapes similar to traditional filament bulbs. Consequently, they are more likely to fit an existing lamp or light fitting.
  • Some are now made with the LEDs arranged in "filaments" to resemble a traditional bulb. The more spread-out light source may be less likely to give you spots before your eyes if you should look directly at them.
  • "Vintage" or "Virtual filament" LED bulbs are designed to mimic "vintage" bulbs. Some are actually LED filament bulbs (as above) some with a flexible LED filament wound into a spiral. In others, the light is directed into a piece of transparent plastic and escapes through its edges and through etchings on its surface, giving a similar decorative effect.

Dimmable?

All filament bulbs are dimmable though they become even more inefficient as they are dimmed. If you want to use a compact florescent or a LED bulb on a dimmer switch you must choose one which is marked as "dimmable", and ensure that your dimmer switch is a modern one designed for low energy bulbs.

What kind of base?

File:Lamp bases.jpg

LED lamps with different bases: from left to right, BC, SES and ES. The middle one is a LED filament lamp.

When replacing a bulb, be sure to check which sort of base it has. Mains bulbs have either a bayonet cap (BC) or Edison Screw (ES). There are different sizes of ES and less often different sizes of BC. It's a good idea to replace an old filament bulb with a much more efficient compact florescent or LED equivalent, which will also run much cooler. However, compact florescents don't always fit an existing bulb holder or shade. If a compact florescent won't fit and you find the LED equivalent too expensive, at least go for a halogen.

Linear bulbs have been used for many years, for example over a shaving mirror, in a cupboard, or over a work surface. These were either filament or florescent. LED equivalents are now available for the linear filament bulbs and also for standard florescent tubes.

How long will it last?

Halogen bulbs are generally designed to last 2,000 hours, roughly double the lifetime of an older tungsten type. A compact florescent might last 10 - 20,000 hours but will grow dimmer as it ages. A LED bulb should last 50,000 hours. Its life is limited more by the electronics in its base than the LEDs themselves.

Premature failures are far from unknown on compact florescent and LED bulbs, often due to poor quality electronic components in the base in cheap Far-Eastern examples. You may wish to keep the receipt if you decide to buy a relatively expensive bulb so you can claim in the case of an early life failure.