How Many Lumens and What Colour Temperature Does Each Room Need?

The three numbers on a bulb box

Most people pick bulbs by wattage out of habit, then wonder why a room feels gloomy or harsh. Three numbers on the pack tell you what the light will actually do: lumens (how much light), Kelvin (how warm or cool it looks) and Ra or CRI (how faithfully it shows colour).

This guide gives you a method for each room: measure, pick a lumen target, split it across several lamps, choose a Kelvin, and check the Ra. It is deliberately separate from our guides on layering light in a living room (where lamps go) and choosing a bulb for a plaster wall light (fittings, caps and heat). Here we deal only with the numbers.

What you need: a tape measure, the floor dimensions of the room, the packs of the bulbs you already own, and a notebook or phone. The sums take about ten minutes.

Lumens, lux and watts: what is what

A lumen (lm) measures the amount of visible light a source gives out, weighted to the sensitivity of the human eye.^[1] A lux (lx) measures how much of that light lands on a surface: one lux is one lumen spread over one square metre.^[2] A watt (W) measures electrical power, not brightness.^[3]

That is why a bigger room needs more lumens. A 1,000 lumen source puts 1,000 lux on one square metre, but only 100 lux when the same light spreads over ten.^[2] Watch the animation: the lamp never changes, only the area it has to cover.

With old filament bulbs, wattage was a proxy for brightness. LEDs broke that link. The Energy Saving Trust gives these approximate equivalents: a 40 W filament bulb is about 470 lumens, 60 W about 800, 75 W about 1,050 and 100 W about 1,520.^[3] An LED giving 800 lumens uses roughly 8 to 12 W, against 60 W for the filament bulb it replaces.^[1] Buy by lumens and you will not go wrong.

What UK standards actually say (and do not)

Many guides quote “recommended lux levels for a living room” as though they were official. They are not. We checked.

• Building regulations cover the efficiency of fixed lighting, not how bright a room must be. In England, Approved Document L (2021 edition incorporating 2023 amendments) expects new fixed lighting in a dwelling to give at least 75 light-source lumens per circuit-watt.^[4][5] The Lighting Industry Association’s summary adds that the document asks only for fixed lighting levels suited to the activity in each space.^[4] Wales and Scotland publish their own versions, and Northern Ireland’s rules differ.^[4]
• CIBSE LG9 is a real lighting guide, but its scope is communal residential buildings such as shared halls and corridors, not the rooms inside a home.^[6]
• CIBSE’s general guidance says typical illuminance in buildings runs from 100 to 1,000 lux and leaves building-by-building values to a separate code.^[7]

So there is no statutory lux figure for a living room. Any per-room number you meet, including ours below, is a rule of thumb. For comparison, Wikipedia’s illustrative table puts “family living room lights” at around 50 lux.^[2] Our rule-of-thumb figures below are higher because they count lumens leaving the bulb, and shades, dark walls and furniture absorb a good share before light reaches the floor. That last point is our reading, not a measured result.

Rule-of-thumb lumens per room

These are the figures lighting designers and retailers commonly use. They are not standards: use them as a starting range, then adjust.

Adjust the range: go to the top for dark walls, dark floors or high ceilings; go to the bottom for pale walls and lots of daylight. The totals are for general light only. Accent lamps (a picture light, a candle-bulb sconce) sit on top and are about mood, not coverage.

Worked example: a 4 m × 5 m living room

Take a typical living room, 4 m by 5 m.

1. Area: 4 × 5 = 20 m².
2. Target: 150 lumens per m² for general light (rule of thumb, top of the range because the walls are mid-tone).
3. Total: 20 × 150 = 3,000 lumens.
4. Split it across at least four sources so no single lamp does all the work: two wall lights at 400 lumens each (800), a floor lamp at 800, a table lamp at 470 and a pendant at 1,050. The total is 3,120 lumens, about 156 per m².
5. Dim it. Dimmable bulbs on a dimmer let you run the room at a third in the evening, about 1,000 lumens, which feels softer without changing a bulb.

Notice what the method avoids: one 3,000 lumen ceiling light. A single overhead source makes shadows under the eyes and flattens the room. The mix above is the layering idea from our layered lighting guide, now with numbers.

Colour temperature (Kelvin) by room

Colour temperature describes the colour of the light itself, in Kelvin (K). Lower numbers are warmer and more orange; higher numbers are whiter and bluer. A candle flame is about 1,850 K and daylight roughly 5,000 to 6,500 K.^[8]

The Energy Saving Trust advises about 2700 K, which it calls very warm, for living areas and bedrooms, and 2700 K to 3000 K warm white for general lighting. It describes 4000 K to 4500 K cool white as a little harsh, but possibly suitable for bathrooms and perhaps kitchens.^[3]

The 2700 K, 2700 to 3000 K and 4000 to 4500 K bands come from the Energy Saving Trust; the room-by-room table is our rule of thumb built on them. One practical rule: keep bulbs within a room within about 300 K of each other, otherwise one lamp looks yellow beside another.

Ra (CRI): will colours look right?

The colour rendering index scores how naturally a light shows colours compared with a reference source; the maximum is 100. Incandescent and halogen lamps score close to 100, a typical white LED scores 80 or more, and high-CRI LEDs reach about 95.^[9] Ra can miss problems with saturated red, which is why some packs also quote R9.^[9]

Rule of thumb: Ra 80 is fine for hallways and landings; look for Ra 90 or more where you judge colour or want warm skin tones and wood to look rich: kitchens, dressing tables, rooms with art, and anywhere with plaster details you have painted a considered colour. It costs a little more per bulb and is one of the cheapest upgrades.

Bulbs and plaster wall lights

If you are lighting from a plaster wall light, the numbers above still apply: pick the lumens first, then check the fitting takes that bulb. Our guide to choosing a bulb for a plaster wall light covers caps, shapes and heat, and wall light height and spacing covers where to hang them. As a rule of thumb, a pair of wall lights at 300 to 450 lumens each gives a living room a soft wash without glare, and the rest comes from lamps.

Common mistakes

• Buying by watts. An LED of 5 to 8 W can match a 40 W filament bulb at about 450 lumens.^[1] Read the lumens.
• One big light. Three or four lamps at lower output beat one bright centre light.
• Mixing Kelvin. A 2700 K lamp beside a 4000 K lamp makes the cooler one look blue.
• Forgetting the dimmer. Check the bulb and the dimmer are compatible; the bulb pack says if it is dimmable.
• Judging by the shop display. Shop lighting is far brighter than a home needs. Use your own room’s area.
• Treating rules of thumb as law. They are a start; your eyes, your walls and your daylight decide the finish.

Quick-reference table

All figures except the 75 lumens per circuit-watt in England and the Energy Saving Trust Kelvin bands are rules of thumb.

Glossary

What to do next

Measure your room, work out your total with the table, and list the lamps you have with their lumens. Replace the worst offenders first: usually harsh cool-white bulbs in living areas. Then read how to layer lighting in a living room for placing the lamps, and see bedroom wall lights and lighting hallways and stairs for those rooms.

Keep reading

• How to layer lighting in a living room
• What bulb to use in a plaster wall light
• Wall light height and spacing
• Bedroom wall lights guide
• Lighting hallways and stairs

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Frequently asked questions

How many lumens do I need per room?

There is no UK standard for rooms in a home, so these are rules of thumb: about 100 to 150 lumens per m² for living rooms and bedrooms, 200 to 300 for kitchens and bathrooms, and 300 to 500 on a desk. Multiply by the floor area to get a total, then split it across several lamps.

How many lumens does a living room need?

As a rule of thumb, 100 to 150 lumens per square metre. A 4 m by 5 m room (20 m²) therefore needs about 2,000 to 3,000 lumens of general light, spread over wall lights, lamps and a ceiling or pendant light, ideally on a dimmer.

What colour temperature is best for a living room?

About 2700 K, which the Energy Saving Trust calls very warm and recommends for living areas and bedrooms. Warm white up to 3000 K also works for general lighting.

Is 4000K too harsh for a kitchen?

The Energy Saving Trust describes 4000 K to 4500 K cool white as a little harsh but possibly suitable for bathrooms and perhaps kitchens. Many people prefer 3000 K to 3500 K in a kitchen that is also a living space.

What is the difference between lumens and lux?

Lumens measure the total light a bulb emits. Lux measures how much of it lands on a surface: one lux is one lumen per square metre. The same lumens over a bigger area give fewer lux.

What does CRI mean on a bulb?

CRI, or Ra, scores how accurately a light shows colours, with 100 as the maximum. A typical white LED scores 80 or more and high-CRI LEDs about 95. Choose 90 or more where colour matters.

Are lumen recommendations law in the UK?

No. Building regulations in England set a minimum efficacy of 75 lumens per circuit-watt for new fixed lighting and ask for light suited to the activity, but they set no lux level for each room.

How many lumens is a 60 watt bulb?

The Energy Saving Trust gives about 800 lumens for the old 60 W filament bulb. An LED of about 800 lumens uses far less power.