Lumens, watts and colour temperature: choosing the right light

In the days of incandescent bulbs, saying 60 W or 100 W was enough to describe brightness. With LEDs we get the same light for far less energy, so brightness is measured in lumens (lm).

Lumens: how much light?

Lumens are the total amount of light a source emits. As a rule of thumb, an old 60 W incandescent bulb gave about 800 lumens. Watts describe consumption; the ratio of the two (lm/W) describes efficiency.

Colour temperature: the tone of the light

• 2700K – 3000K: warm white. Relaxing for living rooms, bedrooms and restaurants.
• 4000K: neutral white. Clear light for kitchens, bathrooms, work areas and shops.
• 5000K – 6500K: cool white. For warehouses, workshops and technical areas.

Avoiding a mix of colour temperatures in one room gives a coherent look. Tunable (CCT) fittings let you change the tone during the day.

CRI: how accurately are colours shown?

The colour rendering index (CRI or Ra) describes how accurately light shows the colours of objects compared with daylight. At home at least 80 is recommended; kitchens, dressing areas and displays benefit from 90 or higher.