Find the right bulb

Replacing a bulb should be straightforward. If the codes and fittings have you puzzled, start with the lamp you already have and work through this checklist before ordering.

1. Keep the old lamp’s details

Photograph the markings on the lamp and any label on the fitting. Look for the manufacturer, product reference, voltage, wattage and colour information. If the markings are faint, keep the old lamp safely until you have identified a suitable replacement.

2. Match the cap and connections

Check how the lamp connects to the fitting: screw, bayonet, pins or another connector. Compare the exact cap code where available, not just its appearance. For pin-based lamps, check the pin number, spacing and layout. A similar-looking base is not enough to establish compatibility.

3. Check the size and shape

Measure the lamp’s overall length and widest point, and compare these with the replacement’s listed dimensions. Make sure there is enough space inside any shade, cover or enclosure.

4. Check electrical compatibility

Compare the replacement’s specifications with the fitting’s requirements and the manufacturer’s instructions. Check the voltage, permitted lamp type and any wattage limit. For lamps used with a ballast, starter, transformer or driver, confirm that the replacement is explicitly suitable for that equipment. Do not assume that an LED lamp is a direct replacement simply because it fits.

5. Choose brightness and light colour

Lumens describe light output, while watts describe power consumption. When comparing different lighting technologies, use the stated lumen output as a starting point for brightness rather than matching watts alone.

Colour temperature is expressed in kelvin (K). Lower values generally give a warmer appearance, while higher values give a cooler appearance. Match the colour designation or kelvin value of nearby lamps if you want a consistent look.

6. Check dimming and special requirements

If the fitting is dimmed, check that the lamp is dimmable and suitable for the dimmer and any control equipment. Also check the product instructions for restrictions on enclosed fittings, operating conditions and intended use. Use only replacements explicitly suitable for specialist applications.

Why an old dimmer can struggle with LED bulbs

Many older dimmers were designed for higher-wattage incandescent or halogen lamps. LED lamps use much less power, so the total load can fall below the dimmer’s minimum operating load. It is not simply that the dimmer cannot recognise the bulb: its electronics may not operate correctly with the lower load or with that particular LED driver.

Symptoms can include flickering, buzzing, an uneven dimming range, lamps cutting out at low settings, or lamps failing to switch on reliably. These symptoms can have other causes too, so they do not automatically mean the bulb is faulty.

A bulb marked “dimmable” is not guaranteed to work with every dimmer. Check the lamp manufacturer’s compatibility guidance and the dimmer’s LED-specific minimum and maximum loads and permitted lamp count. Use the lamps’ actual wattage, not their advertised incandescent-equivalent wattage. A dimmer’s halogen rating is not automatically its LED rating.

An LED-compatible dimmer may be needed. Some combinations use trailing-edge dimming, but do not assume that any trailing-edge dimmer will suit every lamp: follow the manufacturers’ recommendations for the exact models. Where supported, an installer may also need to set the minimum dimming level.

Do not add extra lamps or resistors just to increase the load. If compatibility is unclear, or the dimmer needs replacing or adjusting internally, ask a qualified electrician to check the installation.

Buying a fluorescent or pin-based replacement?

Write down the full lamp reference rather than relying on wattage or pin count alone. For an LED conversion, check the exact fitting and control-gear compatibility and whether installation changes are required. Where a conversion requires rewiring, leave that work to a qualified electrician.

Replace the starter when replacing a fluorescent tube

When replacing a traditional fluorescent tube in a fitting with a separate starter, it is good practice to replace the starter at the same time, using the correct type for the lamp and fitting. An ageing starter can cause starting problems and shorten lamp life. Some fittings use electronic control gear and have no separate starter.

If you are changing to an LED tube, follow that tube manufacturer’s instructions instead. A compatible fitting may require a specified LED starter replacement, not a conventional fluorescent starter. Other LED tubes require different control gear or professional rewiring, so never assume they are interchangeable.

Still unsure? Have these details ready

  • A clear photograph of the lamp’s markings.
  • A photograph of the cap or pins.
  • The lamp’s length and diameter.
  • The fitting’s make, model and label details, if accessible safely.
  • Whether the light is dimmed, and the dimmer’s make and model if known without removing it.

Email us for help finding your replacement

If you have any problems identifying a lamp or choosing a replacement, email sales@4thehome.co.uk with clear images attached. Include photos of the whole lamp, its markings and its cap or pins, along with the details listed above. Tell us about any issues you are experiencing, and we will help you narrow down a suitable replacement.

These details make it easier to narrow down a replacement. Photographs alone cannot confirm electrical compatibility, so check the product specifications and fitting instructions before buying.

Safety first: Switch off the power and let the lamp cool before handling it. Do not open fittings or touch wiring to obtain information. If the lamp is broken, the fitting is damaged, or you are unsure what is safe, stop and ask a qualified electrician.