Choosing lighting and colour temperature

Brightness is lumens, not watts

In the days of incandescent bulbs, the wattage told you how bright a bulb was. But watts measure how much electricity something uses, and the power needed for a given brightness varies hugely with the efficiency of the light source. Efficient LEDs are bright at low wattage, so when choosing one, look for the lumen (lm) figure on the box. Lumens are the total amount of light a source emits. For the same lumens, the product drawing less power is the more efficient one, which feeds straight into your electricity bill. How bright your desk actually gets still depends on the beam angle and the shape of the shade.

Colour temperature puts a number on the colour of light

Colour temperature describes the colour of light in a unit called kelvin (K). Lower numbers look orange, like candlelight or a sunset; higher numbers look white to bluish, like a midday sky. Despite the name, it has nothing to do with how hot the lamp gets. In fact, lower numbers are called warm light and higher numbers cool light. Products are usually sold under labels like the ones below, but exact kelvin values vary by manufacturer, so check the number on the packaging.

• Warm white: about 2700–3000K, a cosy orange-tinged light
• Neutral white: about 4000–5000K, a natural in-between white
• Daylight: about 5700–6500K, a crisp white with a blue tinge

Match the light to the room's use

No single colour temperature is right; choose by what you do in the space. Warm light helps you unwind in a bedroom or in the living room in the evening. It is widely known that long exposure to bright, bluish light late at night can make it harder to fall asleep, so lights near the bed are best warm and dimmable. A desk for reading or studying, or a kitchen counter, is more comfortable with neutral to cool light that shows things clearly. At a dressing table or where you pick clothes, accurate colour matters, so check colour rendering too. If your lights are tunable, set them cooler during the day and warmer at night.

Colour rendering: how natural colours look

At the same brightness and colour temperature, some lights make food look less appetising and skin look dull. This difference is called colour rendering, usually shown as a CRI or Ra index. Measured against natural light, the closer it is to 100, the more natural colours appear. For general home lighting, 80 or above is generally fine, and many people choose 90 or above where colour matters, such as for make-up, painting or photography. If the box gives no colour rendering figure, try shining lamps on the back of your hand or a coloured object in the shop to compare.

Layer your light

One bright light in the middle of the ceiling gives flat shadows and makes a room look flat. It is easier to think of lighting in three layers by role: ambient light that softly lights the whole room, task light for where you work, such as a desk or counter, and accent light that picks out walls, shelves or plants to create atmosphere. In the evening you can often switch off the ambient light and use only task and accent lights, which also uses less electricity. Place a task light on the opposite side to your writing hand so your hand does not cast a shadow.

• Ambient: even light across the room
• Task: desk, worktop, basin
• Accent: walls, corners and shelves for depth

Check before you buy

Before buying a new bulb or fitting, check the socket type you have and the maximum wattage the fitting allows. If the room has a dimmer switch, the product must support dimming, otherwise it may flicker or hum. If your eyes tire easily, products described as low-flicker and fittings with a shade or diffuser to cut glare are more comfortable. Keep the colour temperature consistent within one space. Mixing orange and bluish bulbs in the same room looks messy.

Safety when replacing fittings

Swapping a bulb is usually just a matter of switching off and waiting for it to cool. Removing a ceiling fitting and installing a new one, however, means handling wiring, so always switch off the breaker at the consumer unit first. Turning off the wall switch alone can leave one side of the wiring live. It is work at height, so use a stable ladder and, if possible, have someone hold it. If the wiring is old or the setup unfamiliar, do not push it; call an electrician. If you rent, talk to your landlord before changing fittings.