If you've ever stood in a shop with a bulb in your hand, scanning a box covered in numbers and acronyms — 2700K, 800lm, GU10, IP44, CRI 90, dimmable — and wished someone would just explain it, this is for you.
Home lighting got more technical than it needed to. Energy regulations changed, LED took over, bulbs are now labelled with seven things instead of one. Most of it matters. Some of it really matters. None of it is hard to understand once someone walks you through it.
This is that walkthrough. The complete guide to home lighting, the way we wish someone had explained it to us when we started. By the end you'll know which numbers to care about, which to ignore, and how to make confident decisions for every room in your home.
The seven things you'll see on every bulb box
Every modern LED bulb box gives you a set of specifications. The order varies, the labelling varies, but the same seven things appear on every single one. Once you know what they mean, the choice gets simple.
- Colour temperature — warm or cool light (measured in Kelvin)
- Lumens — how bright the bulb actually is
- Wattage — how much electricity it draws
- Fitting type — how it attaches to your light (GU10, E27, E14, B22)
- CRI — how accurately it shows colours
- Dimmable — whether you can use it with a dimmer switch
- Lifespan — how many hours it should last
The first four are the ones that determine whether a bulb is right for your fitting and your room. The other three are quality markers — important, but secondary. Let's go through each in order.
1. Colour temperature — the most important decision
The K on the box stands for Kelvin, and it tells you how warm or cool the light from the bulb will look. Lower numbers are warmer (yellower); higher numbers are cooler (whiter, then bluer).
The three numbers you'll see most often:
- 2700K — warm white. Cosy, candlelit feel. Best for living rooms, bedrooms, dining rooms.
- 3000K — clean warm. Slightly brighter and clearer. Best for kitchens, bathrooms, home offices.
- 4000K — cool white. Closer to daylight. Best for utility rooms, workshops, walk-in wardrobes.
The single biggest mistake people make is choosing too cool. A 4000K bulb in a living room reads as institutional. When in doubt, go warmer.
The other common mistake: mixing temperatures within one room. A 2700K pendant alongside 4000K downlights creates a visually unsettled space. Pick one temperature for each room and stick to it.
We've written about this in proper depth — read the full guide to bulb colour temperature here.
2. Lumens — how bright is bright?
Wattage used to tell you how bright a bulb was. A 60-watt incandescent was brighter than a 40-watt incandescent. Simple.
LEDs broke that. A 9-watt LED can be as bright as a 60-watt incandescent. So the industry shifted to lumens — a direct measurement of light output, regardless of how much energy the bulb uses to produce it.
Rough lumen guide, per fitting:
| Old incandescent | Equivalent lumens | Typical use |
|---|---|---|
| 40W | 400–500lm | Bedside lamp, ambient mood |
| 60W | 700–800lm | Living room lamp, pendant |
| 75W | 1000–1100lm | Kitchen pendant, bright task |
| 100W | 1500–1600lm | Workshop, garage, utility |
How many lumens per room is a different question — it depends on room size, ceiling height, wall colour, and how many fittings you have. A small dim cosy room might be perfectly lit with 1,500 total lumens. A large kitchen needs more like 5,000–8,000 lumens across all fittings.
Rough guide: aim for around 250–400 lumens per square metre for a living room, 400–600 for a kitchen, 100–200 for a bedroom (you don't want it bright before bed). For a much deeper look at the maths and how to plan room-by-room, see our companion guide on lumens vs watts.
3. Wattage — for energy, not brightness
Wattage is now what it always should have been — a measure of energy consumption. Lower wattage means lower running cost. An 8W LED uses about an eighth of the electricity of a 60W incandescent, for the same light output. Over a year of daily use, that's a real saving — the Energy Saving Trust estimates around £55 a year for a typical UK household switching every bulb to LED.
Don't pick a bulb on wattage alone. Pick on lumens (how bright) and let the wattage be whatever it ends up being. A good modern LED produces roughly 100 lumens per watt — anything less efficient than that is using more electricity than it needs to.
4. Fitting type — the bit that actually has to match your light
This is the only spec that absolutely has to match. The wrong fitting and the bulb won't physically screw into your light.
The four common types in UK homes:
- GU10 — twist-and-lock fitting with two prongs. Used for downlights, spotlights, and many modern pendants. Compact, mains voltage, very common.
- E27 — the standard Edison screw, large. The classic "lightbulb" shape. Used in most table lamps, floor lamps, larger pendants.
- E14 — small Edison screw. Used in chandeliers, smaller pendants, fancier fittings.
- B22 — bayonet cap, the older British standard. Two pins, push-and-turn. Found in older houses and many traditional fittings.
Your existing light fitting will have a specific cap type. Look at the dead bulb or check the fitting's box. Match exactly — there's no flexibility here. The naming follows international standards: the "E" in E27 refers to Edison, with 27 being the diameter in millimetres; "GU10" is the formal designation from the International Electrotechnical Commission, which sets bulb cap standards worldwide.
5. CRI — the spec most people ignore that they shouldn't
CRI stands for Colour Rendering Index. It measures how accurately a bulb reveals the true colours of the things it lights up. The scale runs 0–100, where 100 means perfect daylight rendering. The standard is defined by the International Commission on Illumination (CIE).
- CRI 80 — the bare minimum for residential use. Colours look roughly right, but slightly washed out. Adequate, not great.
- CRI 90+ — significantly better. Reds look red, blues look blue, skin tones look healthy.
- CRI 95+ — premium. Worth it for living rooms, dining rooms, bathroom mirrors (anywhere you care about how things or people look).
Most cheap supermarket LEDs are 80 CRI. The price difference between 80 CRI and 90 CRI is typically a couple of pounds per bulb. In any room where you care about how it feels — and the colours of your food, your fabrics, your face — the upgrade is worth every penny.
6. Dimmable — and why this matters more than people think
Not every LED bulb is dimmable. Look for "dimmable" clearly labelled on the box. A non-dimmable LED on a dimmer circuit will flicker, hum, or just refuse to work.
Three things need to be dimmer-compatible: the bulb, the dimmer switch on your wall, and (sometimes) the fitting itself. Older trailing-edge dimmers can struggle with modern LEDs — if you've fitted dimmable LEDs and they're flickering, the dimmer is the most common culprit, not the bulb.
Why does this matter so much? Because lighting that's the right brightness for cooking is too bright for sitting. Lighting that's right for sitting in the evening is too dim for cleaning. A dimmer fixes that problem entirely. It's the single most underrated upgrade in a British home.
7. Lifespan — and why the numbers are slightly oversold
LED bulb boxes claim 15,000, 25,000, even 50,000 hours of life. At 3 hours of use per day, that's 13–45 years.
In reality? Domestic LEDs typically last 8–15 years of real-world use before fading or failing — still hugely better than the 1,000 hours an incandescent gave you, but not the multi-decade life the box promises. Heat, dimmer compatibility, and switching frequency all shorten lifespan.
Worth knowing: bulbs in enclosed fittings (sealed glass shades, recessed cans without ventilation) run hotter and die sooner. If your fitting is enclosed, look for an LED bulb specifically rated for enclosed fittings.
The IP rating — for bathrooms and outdoors only
If you're choosing a fitting for a bathroom or for outside, you'll see another spec: the IP rating. It tells you how much water and dust the fitting can handle.
- IP20 — indoor only, no water exposure. Most living-room fittings.
- IP44 — splash-resistant. Suitable for bathroom zone 2 (the area around but not directly over a bath or shower).
- IP65 — water-jet resistant. Suitable for bathroom zone 1 (directly over the bath/shower) and outdoor wall lights.
- IP67 — submersible to 1m. For outdoor in-ground fittings and exposed garden lights.
For UK bathrooms, the regulations are strict and grounded in BS 7671 (the IET Wiring Regulations) — the wrong IP rating in the wrong zone is a regulatory and safety issue, not just a preference. Guidance is published by Electrical Safety First. We'd recommend reading our forthcoming bathroom IP zones guide if you're planning bathroom lighting yourself. For outdoor pieces, browse our outdoor lighting — every fitting is rated for the British weather it'll meet.
The three-layer principle — light isn't just one thing
The most overlooked truth in home lighting: a room should be lit by at least three different sources at different heights. The technical term is "layered lighting", and it's the difference between a room that feels alive and one that feels flat.
The three layers:
Ambient
The overall fill of the room — usually the ceiling light, or a combination of ceiling fittings and downlights. Provides general visibility. Our ceiling lights cover this role.
Task
Specific, brighter light for a specific activity — the pendant over a kitchen island, the reading lamp next to a sofa, the wall light over a bathroom mirror. Pendant lights and table lamps are the workhorses here.
Accent
Lower, decorative light — a table lamp, a wall light at sofa height, a low pendant in a hallway. This is what makes the room feel inhabited rather than just illuminated. Wall sconces are the natural accent layer.
A room with only ceiling light feels institutional, no matter what bulb temperature you pick. A room with three or more sources, ideally on different switches, feels considered. Get this principle right and most other lighting questions answer themselves.
If you forget everything else from this guide: aim for three different light sources at three different heights in every room, and put the ones that need to set mood on a dimmer.
The order to fix a room you're not happy with
If you've inherited a room you don't like the feel of, here's the order to address it:
- Check the bulb temperature. If everything's currently 4000K or higher, that's almost certainly the problem. Swap for 2700–3000K and re-judge.
- Add a second source. If there's only a ceiling fitting, add a table lamp or floor lamp. Single-source lighting always feels harsh.
- Fit a dimmer. If you don't have one already, this is usually the biggest atmospheric upgrade available for under £50.
- Reconsider the brightness. Most rooms are over-lit, not under-lit. Try lower-lumen bulbs if dimming alone doesn't soften it enough.
- Then think about new fittings. Often unnecessary if the first four are right.
This order matters because fittings are the most expensive change to make. Fix the bulbs and the dimmer first; new fittings only second.
When you need an electrician
Most UK lighting changes — swapping bulbs, replacing a light fitting on an existing wired circuit, adding plug-in lamps — are within the law for a competent homeowner to do safely.
You need a Part P-registered electrician for: adding new lighting circuits, fitting lights in bathrooms or outdoors, anything involving new wiring beyond the existing fitting. This is both for safety and to comply with UK Building Regulations. Bodies like NICEIC certify electricians to the current standards.
If in doubt, call one. Lighting is one of the most cost-effective places to use professional help — a good electrician can often complete a whole-house lighting upgrade in a day.
Putting it all together — a room you'd want to spend time in
If you're starting a lighting project from scratch, or fixing a room you've inherited, here's the order of decisions:
- Pick the colour temperature (warmth) for the room.
- Calculate roughly how many lumens you need across all fittings.
- Plan three sources at three heights — ambient, task, accent.
- Pick pieces — see living room lighting, kitchen lighting, bedroom lighting for room-specific edits.
- Wire each layer to a dimmer-compatible circuit if possible.
- Choose dimmable LED bulbs with 90+ CRI.
- Live in it for a week. Adjust.
The Enso take
Good lighting is the most transformative — and most underrated — thing you can do to a home. New paint, new furniture, new floors: all marginal compared to changing the way a room is lit. And the principles aren't complicated. Once you understand colour temperature, lumens, and the three-layer principle, the rest follows.
If you're planning a lighting project — a single room or a whole house — and want a second opinion on what you've chosen, drop us a line. We've spent years thinking about this, and we'd rather help you get it right than have you buy something that doesn't work.
