How the room lighting calculator works
Pick the room, enter its size and the height of the ceiling, and say how bright you like it. There are two tabs:
- Lumens needed: how much light the room needs in total, how many bulbs that is, the LED wattage, and how to split it between general, task and accent light.
- Recessed light layout: how many recessed lights to fit, where to place them, and how bright each one should be.
Lumens, not watts
A lumen is a measure of the light a bulb gives out. A watt only tells you how much power it uses. An old 60 W bulb gave about 800 lumens, and an LED bulb gives the same light for about 9 W. So shop by lumens, and use watts to compare running costs.
| Old bulb | Lumens | LED power |
|---|---|---|
| 40 W | 450 | about 5 W |
| 60 W | 800 | about 9 W |
| 75 W | 1100 | about 12 W |
| 100 W | 1600 | about 16 W |
How many lumens does a room need?
The usual method is lumens per square foot. The calculator uses these starting figures and then adjusts them for the ceiling height, the colour of the walls and your taste.
| Room | Lumens per sq ft |
|---|---|
| Hallway or stairs | 10 |
| Bedroom | 15 |
| Living room | 20 |
| Dining room | 30 |
| Kitchen and laundry | 35 |
| Home office | 45 |
| Garage or workshop | 50 |
| Bathroom | 70 |
Adjustments: a 9 ft ceiling needs about 10% more light, 10 ft about 25% more and 12 ft about 50% more, and dark walls absorb light, so they need up to 30% more. Choose “soft” for a relaxed room and “bright” if you like a lot of light, or if you have older eyes.
Use three layers of light
- General (ambient): the overall light, from ceiling lights or a pendant.
- Task: light where you work, such as under-cabinet lights, a desk lamp or the mirror light.
- Accent: light that adds depth, such as a wall light, a picture light or a lamp in a corner.
One ceiling light gives a flat room. A mix of three layers, on different switches or dimmers, makes it feel better, and lets you change the mood.
The colour of the light
- 2700K: warm white. The cosy glow of an old bulb, good for living rooms and bedrooms.
- 3000K: soft white. A little crisper, good for kitchens, bathrooms and dining rooms.
- 4000K: neutral white. Clear and bright, for laundry rooms, home offices and garages.
- 5000K: daylight. Very white, and good for detailed work, but cold in a living space.
Use the same colour temperature in rooms that you can see at the same time. Choose a colour rendering index (CRI) of 90 or higher, so that colours, skin and food look natural.
How to space recessed lights
A simple rule is to space them about half the ceiling height apart, so an 8 ft ceiling gets a light about every 4 ft. A wider spacing gives pools of light and a softer look, and a closer spacing gives a bright, even light. Keep the outer lights about half that distance from the walls, or about 2 ft, so the walls are not washed with light unless you want it.
Check the amount of light, not only the spacing. If the layout gives too little light per fitting, add more lights, or use brighter ones.
Worked examples
A 14 × 12 ft living room, 8 ft ceiling
The room is 168 sq ft at 20 lumens per sq ft, which is 3,360 lumens. That is five 800-lumen bulbs, or about 37 W of LED. Use most of it as general light, with the rest on lamps and accent lights.
A 14 × 12 ft living room with recessed lights
With standard spacing of about 5 ft, you can fit 3 lights along the length and 2 across the width, which is 6 lights. Each one should give about 560 lumens.
An 8 × 5 ft bathroom
The room is 40 sq ft at 70 lumens per sq ft, which is 2,800 lumens, most of it at the mirror. That is four 800-lumen bulbs.
Common mistakes
- Buying by watts. Watts do not tell you how bright an LED is.
- One light in the middle. It leaves the corners dark and casts shadows.
- Mixing colour temperatures. A 2700K lamp next to a 4000K downlight looks wrong.
- No dimmer. A dimmer lets one set of lights work for both a party and a quiet evening. Check that the bulbs are dimmable.
- Forgetting the mirror. A light above the bathroom mirror only casts shadows on your face.
Tips
- Put the lights on dimmers, so you can adjust the level.
- Use lamps at eye level to make a room feel warmer.
- Choose fittings that are rated for damp areas in bathrooms and outdoors.
- Buy one bulb first and try it for a week.
