Foundation 2The numbers that matter
Four numbers on a datasheet tell you most of what a light will do in a room. For the full glossary, see Technical Lighting 101.
Colour temperature (Kelvin, K) sets the mood. Lower is warmer and more relaxing; higher is cooler and more alerting.
| Colour temperature |
How it looks |
Where we use it |
| 2700K |
Warm, golden, like late-evening light |
Living rooms, bedrooms, dining, outdoors |
| 3000K |
Warm white, a little crisper |
Kitchens, bathrooms, desks in shared rooms |
| 3500K–4000K |
Neutral white |
Dedicated home offices, commercial spaces |
| 5000K and above |
Cool, bluish daylight |
Workshops and detailed task areas only |
Pick one colour temperature per room and stick to it. Mixing 2700K and 4000K in the same space makes both look wrong.
Brightness (lumens, lm) is how much light comes out. Compare lumens, not watts. As a guide, 450 lm is a soft glow (an old 40W bulb), 800 lm lights a small room (60W), and 1,600 lm suits a large space (100W).
Colour rendering (CRI) is how true colours and skin tones look, out of 100. Choose CRI 90 or higher at vanities, in kitchens and anywhere art is lit.
Dimming turns one light into several. Put your brightest layer on a dimmer, and check the fitting's dimming type matches the dimmer before installation.