Light Bulb Finder: Bulb Fittings, Lumens and Colour
Not sure which bulb you need? Tap the fitting on your old bulb to see what it's called and how to spot it, then find the LED to replace it: the lumens to look for, its wattage, warm or cool white, and what you'll save. Keep a list of every bulb in your home or building, with spares, and export it.
No sign-up required. Free to use, with every figure explained on this page. Last reviewed October 2026.
Find your bulb
Light Bulb Finder
Tap the fitting on your old bulb, say what it was, and get the LED to buy: brightness in lumens, watts and colour. Add each one to My bulbs to keep a list of every bulb in your home or building.
1 Which fitting?
Look at the end of the old bulb, where it goes into the light.
Bulb shape
2 What was in it?
Old bulb type
3 Colour and extras
Light colour
Beam angle
Where it goes
On a dimmer?
The bulb to buy
E27 LED
Brightness
806 lm
LED power
6–10 W
Saving a year
0 €
About this fitting
My bulbs 0
Saved in this browser only; nothing is sent anywhere. Export a CSV to keep a copy or move the list to another device.
Stock list: the same bulbs added together
| Bulb | Fitted | Spares |
|---|
How it works: brightness is in lumens (lm), not watts. Old bulbs are converted with the equivalence figures from the EU lighting rules (60 W = 806 lm, 100 W = 1,521 lm), which makers still print on the box; spotlights, capsules, energy-saving bulbs and tubes use typical figures for their type. LED watts assume a typical efficiency for that kind of bulb (about 100 lumens per watt for a standard bulb), shown as a range. The saving is the difference in watts × hours a day × 365 × your price per kWh.
A guide only. Light output and wattage vary by make, so check the box. Switch off at the wall or the fuse box before changing a bulb, and let halogen bulbs cool first. Changing transformers or converting fluorescent fittings is a job for an electrician. Actual savings vary.
How it works
Fitting, brightness, colour
Three things decide which bulb to buy. Get them right and the new bulb fits, gives the same light and looks the same as the ones around it.
The fitting
The cap is the end that goes into the light. Screw caps are E plus their width in mm (E27, E14) and bayonets are B (B22 in the UK and Ireland). A G means pins: GU10 spots have pins 10 mm apart, G9 capsules 9 mm. Some, like MR16 spots and G4 capsules, run on 12 V.
Lumens, not watts
Watts are the power a bulb uses; lumens are the light it gives. An old 60 W bulb gives 806 lumens, and an LED gives the same from about 8 W. For a standard LED bulb, the watts are roughly the lumens ÷ 100; spotlights need a little more.
Colour in kelvin
2700 K is the warm white of old bulbs, 3000 K is like halogen, 4000 K is a cooler, neutral white and 6500 K is daylight. On tubes and some bulbs the colour is a code: 830 means good colour rendering (the 8) and 3000 K (the 30).
Examples
Old bulbs and the LEDs that replace them
Common bulbs, the LED brightness and power to look for, and what one bulb saves a year, worked out with the finder above.
Saving per bulb, used 3 hours a day at 26p a kWh. Ordinary bulbs use the EU equivalence figures; tubes and PL lamps need fewer lumens as LEDs because they shine one way only. LED wattage varies by make, so check the lumens on the box.
Tips
Buying and keeping track of bulbs
A few checks save a wasted trip to the shop, and a list saves a lot more if you look after many lights.
Keep a list
In a hotel, holiday let, office or a large home, add each light to My bulbs with where it is and the exact spec. The stock list adds up the same bulbs so you know what spares to keep, and replacements match: no more 4000 K next to 2700 K in one corridor.
Check the catch
Dimmers need dimmable LEDs and an LED dimmer. 12 V spots depend on their transformer. Closed or fire-rated downlights need LEDs made for enclosed fittings. LED tubes must match the fitting's ballast, or the fitting is rewired.
Count the saving
Swapping a 50 W halogen spot for a 5 W LED cuts its running cost by about 90%, and an LED lasts 15 to 25 times longer. See what your other appliances cost to run with the Electricity Cost Calculator.
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Common questions
Frequently asked questions about light bulbs
Common questions about bulb fittings, lumens, colour and changing to LED.
What are the different types of light bulb fittings?
The most common are screw caps (E27 and the smaller E14), bayonet caps (B22 and the smaller B15, standard in the UK and Ireland), GU10 spotlights with two thick pins, 12 V MR16 (GU5.3) spots with two thin pins, small G9 and G4 capsules, R7s linear halogens, and fluorescent tubes (T8 and T5) and PL lamps. The finder above draws each one and shows how to spot it.
What is the difference between E27 and B22?
Both are full-size mains fittings about the same width. An E27 screws in, and is the standard across mainland Europe. A B22 (bayonet) pushes in and twists, with two small pins on the side, and is the standard in the UK and Ireland. LED bulbs are sold in both, and adapters exist if you need to use one in the other.
How many lumens is a 60 W bulb?
An ordinary 60 W bulb gives about 806 lumens, the figure from the EU lighting rules that makers still print on the box. An LED bulb gives that from about 8 W (6 to 10 W, depending on the make). A 40 W bulb is about 470 lumens and a 100 W bulb about 1,521.
How do I convert watts to lumens?
It depends on the type of bulb. Ordinary bulbs give about 12 to 15 lumens per watt (40 W = 470 lm, 60 W = 806 lm, 100 W = 1,521 lm), halogen about 15, energy-saving bulbs about 60, and LEDs about 100. To find an LED's watts, divide the lumens you want by about 100, or 75 for spotlights.
Should I choose warm white or cool white?
Warm white (2700 to 3000 K) gives the cosy, yellowish light of old bulbs and suits living rooms, bedrooms and hotel rooms. Cool white (4000 K) is brighter and more neutral, good for kitchens, garages, workrooms and back-of-house areas. Daylight (6500 K) is very white and suits workshops. Keep one colour within a room.
What do the numbers 830 or 840 on a bulb mean?
The first digit is the colour rendering (CRI): 8 means 80 or more, which is good and the usual for homes, and 9 means 90 or more, where colours look natural. The last two digits are the colour temperature divided by 100: 830 is 3000 K warm white, 840 is 4000 K cool white and 865 is 6500 K daylight.
Can I replace a halogen spotlight with an LED?
Yes. A mains GU10 is a straight swap. A 12 V MR16 (GU5.3) runs from a transformer, and old ones built for halogen can make LEDs flicker or not light at all, so buy LEDs listed as compatible with electronic transformers, or have the transformer replaced with an LED driver. In a closed or fire-rated downlight, use an LED made for enclosed fittings.