The LED replacement bulb market in the UK is full of products described in watts. This is a problem, because watts measure energy consumption, not brightness. When you replace an old 60W incandescent with a 10W LED, the 10W tells you what it costs to run. The lumen figure on the same box tells you how bright it will be. Buyers who do not know this read "10W" and assume the replacement will be noticeably dimmer than the old 60W. It will not, if the lumen figure is right. This guide gives you the conversion table and the other things to check before you buy.
Key Takeaways
- A 60W incandescent produced around 800 lumens; its LED equivalent uses 6-10W for the same output
- A 100W incandescent produced around 1,400 lumens; a good LED produces this at 12-15W
- The lumen figure, not the watt figure, determines how bright the replacement will be
- Check the cap type (GU10, E27, B22, E14, G9) before ordering; a wrong cap type will not fit
- Dimmable LED bulbs require a compatible LED dimmer switch; not all dimmers are compatible
The quick answer: To replace a 60W incandescent, look for an LED with 800 lumens output. To replace a 40W, look for 450 lumens. To replace a 100W, look for 1,400 lumens. The wattage of the LED replacement is irrelevant to brightness; it will be roughly 6-14W depending on the quality of the bulb. Check the cap type matches your fitting (GU10, E27, B22, or E14 are the most common UK types) and whether you need a dimmable bulb. The full conversion table is below.
The LED Bulb Replacement Chart: 25W to 150W Equivalents
| Old Incandescent Wattage | Lumen Output | LED Replacement Wattage (approx) | Typical LED Type |
|---|---|---|---|
| 25W | 230 lm | 2-4W | E14 candle, G9 capsule |
| 40W | 450 lm | 4-6W | E27 GLS, B22 GLS, E14 candle |
| 60W | 800 lm | 6-10W | E27 GLS, B22 GLS, GU10 spotlight |
| 75W | 1,000 lm | 8-12W | E27 GLS, B22 GLS |
| 100W | 1,400 lm | 12-15W | E27 GLS, B22 GLS, large spotlight |
| 150W | 2,000 lm | 18-22W | E27 large GLS, R7s linear |
These are approximate figures. LED quality varies significantly between manufacturers. A cheap 8W LED may produce 600 lumens. A well-engineered 8W LED may produce 900 lumens. When buying LED replacements for rooms where brightness matters, check the lumen figure on the packaging, not the wattage.
Why LED Wattage Is Not a Reliable Brightness Indicator
LED technology converts electricity to light more efficiently than any other domestic light source. But efficiency varies by product. The metric that measures this is luminous efficacy: lumens per watt (lm/W). A good LED bulb achieves 90-120 lm/W. A poor one may achieve only 60-70 lm/W. Two 10W LED bulbs from different manufacturers can produce meaningfully different amounts of light.
This is why the equivalent wattage figure printed on LED packaging ("replaces 60W") is a marketing statement, not a technical guarantee. The actual brightness guarantee is the lumen figure. A bulb that claims to replace 60W but only produces 600 lumens (instead of 800) is under-delivering. Check the lumen figure. If a bulb does not state its lumen output, do not buy it.
Choosing the Right LED Bulb Cap Type
The cap type is the physical fitting that connects the bulb to the lamp holder. A GU10 will not fit an E27 holder. An E14 will not fit a B22. Before ordering any LED replacement, confirm the cap type of your existing fitting.
| Cap Type | How to Identify It | Common Fitting |
|---|---|---|
| GU10 | Two small pins that rotate to lock (twist-and-lock) | Recessed downlights, surface spotlights |
| E27 | Large screw thread, 27mm diameter | Pendants, floor lamps, table lamps, decorative fittings |
| E14 | Small screw thread, 14mm diameter | Chandelier arms, candelabra fittings, small decorative pendants |
| B22 | Two pins that push and twist to lock (bayonet) | Traditional UK pendants, older table lamps |
| G9 | Two small looped pins, push-in | Wall lights, small decorative fittings, some undercabinet |
| G4 | Two fine pins, 4mm apart, push-in | Very small decorative fittings, some undercabinet |
GU10 and E27 cover the majority of residential lighting in UK new-build and renovated properties. B22 is the classic UK fitting still found in many older homes. E14 and G9 are common in wall lights and chandelier-style fittings.
Dimmable LED Bulbs: What to Check Before You Buy
Not all LED bulbs are dimmable. A non-dimmable LED connected to a dimmer switch will flicker, buzz, or fail prematurely. A dimmable LED connected to an incompatible dimmer switch will do the same. There are two things to check:
First: the bulb must be explicitly labelled as dimmable. "Dimmable" on the packaging is the required statement. If it is not there, the bulb is not dimmable.
Second: the dimmer switch must be LED-compatible. Older TRIAC (leading-edge) dimmers were designed for halogen and incandescent loads. They do not work well with most LED bulbs. A trailing-edge (MOSFET) LED dimmer is the compatible type. Many dimmer switches have a wiring label inside the backplate that identifies the type. If the dimmer is more than five years old and was installed with halogen fittings, replace it with an LED-compatible trailing-edge dimmer when you upgrade to LED.
Minimum load is the other variable. LED dimmers have a minimum load rating. A room with four 6W LED downlights (24W total) on a dimmer rated 40W minimum will not dim correctly. The total wattage of the LEDs must exceed the dimmer's minimum load. Check both the minimum and maximum load on the dimmer specification before buying dimmable LEDs for a circuit with an existing dimmer.
For GU10, E27, and B22 LED replacement bulbs, check the lighting accessories section. For fittings that accept GU10 bulbs, see recessed spotlights and indoor spotlights. For pendant and table lamp fittings using E27, browse pendant lights and table lamps.
Frequently Asked Questions About LED Bulb Replacement
What LED bulb replaces a 60W incandescent?
An LED producing 800 lumens. In wattage terms, expect a quality LED to achieve this at 6-10W. The exact wattage depends on the LED quality and efficiency. Always check the lumen figure rather than relying on the equivalent wattage claim on the box.
Do LED bulbs fit in old light fittings?
Yes, as long as the cap type matches. GU10 LEDs fit GU10 holders. E27 LEDs fit E27 holders. E14 fits E14, B22 fits B22. LED bulbs are designed as direct replacements for the same cap type in existing fittings. No adaptor is required for like-for-like replacement.
Can I use any LED bulb in a dimmable fitting?
No. You need an LED that is explicitly labelled dimmable, used with a compatible LED dimmer switch. A non-dimmable LED in a dimmer circuit will flicker or fail. A dimmable LED with an incompatible (TRIAC) dimmer will also perform poorly. Replace old TRIAC dimmers with trailing-edge LED dimmers when upgrading to dimmable LED.
Why does my LED bulb flicker after replacement?
The most common cause is an incompatible dimmer switch. Replace the dimmer with an LED-compatible trailing-edge dimmer. The second cause is total load below the dimmer's minimum: if the combined LED wattage is below the dimmer's minimum load, the circuit does not function correctly. Check both the dimmer minimum and maximum load ratings against the LED wattage total.
Do LED bulbs get hot?
Much less than halogen. A GU10 halogen at 50W generates significant heat. A 6W GU10 LED produces minimal heat at the light-emitting surface. The LED driver (the electronics inside) does generate some heat and should not be enclosed in an airtight fitting without a rated fire-proof downlight cover. Standard lamp shades and open pendants present no heat issue with LED at 10W or below.
