Light color temperature simulator: 2700K vs 3000K vs 4000K
See a room under two lamps side by side — 2700 K against 3000 K, 3000 K against 4000 K, or any color temperature from 1800 to 6500 K. Use a sample living room or bedroom, your own photo or video, or the camera. Drag the line to compare. Everything runs on your device.
How far to trust this. It is a physics model, not a photo of a real bulb. The colors of the surfaces are guessed from the picture, the lamp is an ideal source (a black body), and brightness is not modelled. Real LED bulbs with the same kelvin number can look different from each other, and your screen changes colors too.
“Photo” shows the room as a camera set to daylight would record it; in the room your eye adapts within minutes and the tint looks much weaker — switch to “Eye” to see that.
A model, not a photo of a real lamp: each color’s reflectance is guessed from the picture, the lamp is an ideal black body, and the camera is assumed to have been set to daylight. Your screen adds its own shift.
2700K vs 3000K
Both are warm white. 2700 K is the warmer, more orange-yellow of the two; 3000 K is a little whiter, with less yellow. The step is small: a white wall on a daylight-balanced photo moves from #FFAD59 to #FFB86D, ΔE 2000 3.2, or 37 mired (370 to 333; a mired is a million divided by the kelvin number). The difference shows most when the two are side by side; after a few minutes in one room the eye adapts and it shrinks further. LEDVANCE, a lamp maker, suggests 2700 K for living rooms and bedrooms and 3000 K for offices, shops, classrooms and homes; ENERGY STAR puts both in one “soft white, warm white” band, “ideal for most indoor applications”.
- White wall#FFAD59
- Wood#913F00
- Blue fabric#31384E
- White wall#FFB86D
- Wood#914405
- Blue fabric#303C5C
As a camera set to daylight would record them; computed with the same model as the simulator, from white wall #FFFFFF, wood #96643C, blue fabric #2850C8 in daylight. After the eye adapts (“Eye” view) the walls of both look white, and the wood and the blue differ by only ΔE 2000 0.7 and 0.0.
3000K vs 4000K
This step is larger: from warm white to neutral white. A white wall on a daylight-balanced photo moves from #FFB86D to #FFD3A5, ΔE 2000 9.0 — 2.8 times the step from 2700 to 3000 K — or 83 mired (333 to 250). On such a photo wood comes out less orange and blue fabric bluer at 4000 K (swatches below). ENERGY STAR puts 3000 K in its “soft white, warm white” band, “ideal for most indoor applications”, and 4000 K in its “neutral white, cool white” band, “good for kitchens and work spaces”.
- White wall#FFB86D
- Wood#914405
- Blue fabric#303C5C
- White wall#FFD3A5
- Wood#93511E
- Blue fabric#2D4485
As a camera set to daylight would record them; computed with the same model as the simulator, from white wall #FFFFFF, wood #96643C, blue fabric #2850C8 in daylight. After the eye adapts (“Eye” view) the walls of both look white, and the wood and the blue differ by only ΔE 2000 1.3 and 0.5.
White under common bulb temperatures
A white wall on a photo taken with daylight white balance, at the nominal color temperatures of LED lamps in ANSI C78.377-2024. Computed, not photographed.
- 1800 K#FF7E00
- 2000 K#FF8B16
- 2200 K#FF962F
- 2500 K#FFA449
- 2700 K#FFAD59
- 3000 K#FFB86D
- 3500 K#FFC78B
- 4000 K#FFD3A5
- 4500 K#FFDEBC
- 5000 K#FFE6D0
- 5700 K#FFF0E7
- 6500 K#FFF8FE
How the simulation works
The picture is taken to be shot in daylight with the camera balanced for daylight, so a white wall is white. For each color the page guesses a reflectance spectrum from 380 to 750 nm with spectral.js, lights it with a black body at the chosen temperature (Planck’s law), and turns the result into a screen color through the CIE 1931 observer. In the “Eye” view a Bradford chromatic adaptation then moves the light’s white back to the screen’s white, the way the eye adjusts. For speed the result is fitted to one 3×3 matrix per temperature and applied on the graphics chip. In our test on more than 500,000 colors the fit stays within ΔE 2000 2.6 of the full calculation from 2500 K up, 3.7 at 2200 K and 6.8 at 1800 K, where the most saturated colors leave what a screen can show.
The sample rooms
Living room: photo “Living room” by Jarosław Ceborski (2017). Bedroom: photo “NY loft bedroom” by Gabriel Beaudry (2016). Both are released into the public domain under CC0 and come from Wikimedia Commons (living room, bedroom). They were chosen as references: daylight from a window, white walls, wood, and a few saturated colors, so warm and cool light both show clearly. Both are daytime photos on purpose: a photo taken at night is already lit by a lamp of unknown color, and the model would add a second lamp on top of it.
Light color temperature: questions
- 2700K vs 3000K: what is the difference?
- A small one. 2700 K is a little more orange; 3000 K a little more yellow-white. On a photo taken with daylight white balance a white wall comes out about #FFAD59 at 2700 K and #FFB86D at 3000 K, a difference of ΔE 2000 3.2. Between 3000 K and 4000 K it is 9.0, and between 4000 K and 5000 K 8.4: the 300 K step from 2700 to 3000 K is much smaller than the 1000 K steps above it.
- 3000K vs 4000K: what is the difference?
- A larger one than between 2700 K and 3000 K. 3000 K is a warm white, 4000 K a neutral white. A white wall on a daylight-balanced photo is about #FFB86D at 3000 K and #FFD3A5 at 4000 K, ΔE 2000 9.0 — 2.8 times the step from 2700 to 3000 K. ENERGY STAR’s bulb guide puts 3000 K in its “soft white, warm white” band and 4000 K in its “neutral white, cool white” band.
- Which rooms suit 2700K, 3000K and 4000K?
- It is largely taste, but the published advice is consistent. ENERGY STAR calls 2200–3000 K (soft and warm white) “ideal for most indoor applications” and 3500–4100 K (neutral and cool white) “good for kitchens and work spaces”. LEDVANCE, a lamp maker, suggests 2700 K for living rooms and bedrooms and 3000 K for offices, shops, classrooms and homes. Try your own room in the simulator before you buy.
- Why does the room look so orange?
- The “Photo” view shows the room as a camera locked to daylight white balance would record it, the way warm light looks in a photo next to a window. Your eye does not stay like that: after a few minutes in the room it adapts and white looks almost white again. The “Eye” view shows that adapted state, taking the adaptation as complete.
- Why does the “Eye” view hardly change?
- Because adaptation removes most of the tint. What is left is how the light renders colors: under warm light blues and violets lose some saturation and reds and woods gain some. The lamp here is an ideal black body, which renders colors very well; many real LED lamps, especially with a low CRI, change colors more than this.
- Can I see my own room?
- Yes. Press “Photo or video” and pick a picture of your room, or use the camera. For the closest result take the photo in daylight with the lamps off and the phone on automatic white balance. The picture stays on your device and is not uploaded.
- Is this exactly how my bulb will look?
- No. It is a model. The spectrum of each surface is guessed from its color in the picture, the lamp is an ideal black body at the chosen temperature rather than a real LED, brightness is not modelled, daylight mixing with lamplight is ignored, and your screen and the original photo add their own color shifts. Use it to compare temperatures with each other, not to predict one exact color.
Sources
- International Commission on Illumination (CIE) (2019). Colour-matching functions of CIE 1931 standard colorimetric observer (dataset), 360–830 nm in 1 nm steps, from CIE 018:2019. Licence CC BY-SA 4.0. DOI
- NIST, CODATA 2022 recommended values: second radiation constant c₂ = 1.438 776 877… × 10⁻² m K (exact). Link
- spectral.js: Kubelka-Munk paint mixing in JavaScript (MIT licence). Link
- Bradford chromatic adaptation transform, linear form: the cone matrix CAT_BRADFORD of the colour-science library, which cites Lindbloom B. (2009), Chromatic Adaptation. Link
- Livingston J. (3 Feb 2025). ANSI C78.377 adds two new CCTs. Designing Light. On the 2024 edition of ANSI C78.377 (chromaticity of solid-state lighting products): nominal CCTs 2200–6500 K, plus 1800 and 2000 K added in 2024. A trade article; the standard itself is a paid document. Link
- US EPA, ENERGY STAR (2020). LED Bulbs Made Easy: light bulb purchasing guide. Color/appearance scale: 2200–3000 K soft white, warm white, “ideal for most indoor applications”; 3500–4100 K neutral white, cool white, “good for kitchens and work spaces”; 5000–6500 K daylight, “good for reading”. Link
- LEDVANCE. 2700K vs. 3000K — What’s the Difference? (lighting basics blog, undated). 2700 K: “warm yellow light”, for living rooms, bedrooms, restaurants and hospitality; 3000 K: “warm white light” with fewer yellow and orange tones, for retail, offices, classrooms and residential spaces. A lamp maker’s article. Link