The Kelvin number on a light bulb box tells you more about how a room will actually feel than the wattage does. Here's how to read it in plain numbers.
What Kelvin (K) measures
Kelvin describes the color of the light itself, from warm and yellowish at lower numbers to cool and bluish at higher numbers. It has nothing to do with brightness — that's measured separately, in lumens.
A simple guide by room
| Kelvin range | How it looks | Good for |
|---|---|---|
| 2700K–3000K | Warm white, yellowish | Bedrooms, living rooms |
| 3500K–4100K | Neutral white | Kitchens, bathrooms, garages |
| 5000K–6500K | Daylight, bluish white | Workshops, task lighting, security lights |
Why CRI matters as much as brightness
CRI (Color Rendering Index) measures how accurately a light shows true colors, on a scale up to 100. Cheap bulbs can have surprisingly low CRI even when they're plenty bright, which makes food, skin tones and paint colors look slightly off. For kitchens, bathrooms and anywhere color accuracy matters, look for a CRI of 90 or higher.
Brightness and color temperature are two different things
A bulb can be very bright and still warm-colored, or dim and cool-colored — lumens and Kelvin are independent numbers. Check both on the packaging rather than assuming one tells you the other.