The kelvin (K) number on a bulb is the color of its light, not how bright it is. Lower numbers look warmer and more yellow; higher numbers look cooler and bluer. 2700 K (soft white) is a warm, yellowish light, 3000 K (warm white) is a touch whiter, 4000 K (cool white) is white with a slight blue tint, and 5000 K (daylight) is a cool, bluish white. Which one looks right is your call.
2700 K and 3000 K sit together in ENERGY STAR’s warm band, named Soft White and Warm White, so they look alike; 3000 K is only slightly more neutral. 4000 K is in the next band, Neutral or Cool White, so going from 3000 K to 4000 K is the bigger step. 5000 K starts the Daylight band.
What the kelvin number means
Kelvin is a temperature scale. A bulb’s number is its correlated color temperature: the temperature of an ideal glowing object (a blackbody) whose light comes closest in color to the bulb’s. On the box it stands for the light’s color, or appearance.
Light colors compared
Light bulb colors by kelvin
| Kelvin | ENERGY STAR name | How it looks | ENERGY STAR’s suggestion |
|---|---|---|---|
| 2700 K | Soft white | Warm, yellowish | Most indoor uses |
| 3000 K | Warm white | Warm, a little more neutral than 2700 K | Most indoor uses |
| 3500 K | Neutral white | Neutral, between warm and cool | Kitchens and work spaces |
| 4000 or 4100 K | Cool white | White with a slight blue tint | Kitchens and work spaces |
| 5000 K | Daylight | Cool, bluish white | Reading |
| 6500 K | Daylight | The coolest and bluest of these | Reading |
ENERGY STAR’s names and suggestions are one source’s view, from before its bulb program ended on December 31, 2024. The color is your choice; makers name colors differently, so go by the kelvin number.
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Where each number sits on the Lighting Facts label
The color is the Light Appearance line on the box’s Lighting Facts label: the kelvin number, plus a marker on a scale from 2,600 K at the left end to 6,600 K at the right. The marker is placed in proportion along the scale:
Online listings only have to give the number, such as 2700 K.
The names on the box
The names in the chart are the ones ENERGY STAR recommended for packages. Makers didn’t have to use them, and their names vary:
- GE’s Relax HD bulbs come in Soft White (2700 K) and Warm White (3000 K), matching ENERGY STAR.
- Feit’s color guide calls 3000 K Bright White, and the same page lists its color-selectable bulbs as 2700 K warm white and 3000 K soft white.
- A 2009 ENERGY STAR brochure for CFLs used Bright White for the band from 3500 to 4100 K.
- Warmer still, 2200 K (amber light) and 2500 K (sunset light) were names ENERGY STAR allowed only on filament-style bulbs.
“Soft white” can mean 2700 K or 3000 K, and “bright white” can mean 3000 K or a much cooler light. Check the kelvin number.
Things to weigh
- The other bulbs in the room. Very warm and very cool bulbs together, such as 2700 K and 5000 K, can look unbalanced. Check the number on the bulbs already there.
- The look of old incandescent bulbs. ENERGY STAR described the 2700 to 3000 K band as their standard color, and 2700 K is the warmer end of it.
- How true colors look. That is a separate rating, color rendering (below): two bulbs with the same kelvin number can show colors differently.
- A dimmer. Dim-to-warm bulbs lower their color temperature as they dim, the way incandescent bulbs did. For dimming itself, see LEDs on a dimmer.
- Not sure yet. Color-selectable bulbs switch between colors. Feit’s color-selectable bulbs and fixtures switch between 2700, 3000, 4000 and 5000 K; depending on the model, the color is set by a switch or dial on the bulb, or by turning the light off and on quickly.
Color rendering (CRI)
CRI measures how much the colors of objects shift under a bulb, compared with a reference light of similar color temperature. The highest possible is 100. It isn’t on the Lighting Facts label, so it’s found in the maker’s specs: GE lists 90 for its 75 watt replacement soft white A19, and Feit lists 90 for its GU24-base soft white A19. ENERGY STAR required a CRI of at least 80 for the LED bulbs it certified.
Picked a color? Now the brightness.
Watts to lumens