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Interactive simulator

Blackbody Color Temperature Simulator

Move temperature and watch the spectrum peak shift from infrared toward visible wavelengths while radiated power rises steeply.

Parameters
Color temperature T
K

Absolute temperature of the blackbody — the only quantity that sets the color.

Sweep (auto ping-pong)

While playing, the temperature sweeps automatically between 1000K and 12000K. Moving the slider pauses it.

Common light-source presets
Results
—
Color temperature
—
CIE x, y chromaticity
—
sRGB approx. color
—
Descriptor
Blackbody glow color & spectrum tint
Top: the actual apparent color of the blackbody lamp. Bottom strip: the visible spectrum (380–700nm), with brightness weighted by the Planck radiance at this temperature. As temperature rises the peak shifts toward shorter (bluer) wavelengths.
CIE chromaticity diagram & Planckian locus
The horseshoe is the CIE 1931 chromaticity diagram. The black curve is the Planckian locus; the white dot is the current operating point. Reference sources are marked with circles.
Planck spectral distribution
Planck’s law $B_\lambda(T)$ plotted versus wavelength. The shaded band is the visible range (380–700nm). The peak wavelength follows Wien’s displacement law $\lambda_{max}=b/T$.
Theory & Key Formulas

$$B_\lambda(\lambda,T)=\frac{2hc^2}{\lambda^5}\frac{1}{e^{hc/\lambda k T}-1}$$

Planck’s law: the spectral radiance of a blackbody at wavelength $\lambda$ and temperature $T$. $h$ Planck constant, $c$ speed of light, $k$ Boltzmann constant.

$$X=\int B_\lambda\,\bar x(\lambda)\,d\lambda,\quad Y=\int B_\lambda\,\bar y\,d\lambda,\quad Z=\int B_\lambda\,\bar z\,d\lambda$$

Integrate the spectrum against the CIE color-matching functions $\bar x,\bar y,\bar z$ to obtain the XYZ tristimulus values. Chromaticity is $x=X/(X{+}Y{+}Z)$, $y=Y/(X{+}Y{+}Z)$. An XYZ→sRGB transform yields the on-screen color.

$$\lambda_{max}=\frac{b}{T},\quad b=2.898\times10^{-3}\,\mathrm{m\cdot K}$$

Wien’s displacement law: the higher the temperature, the shorter (bluer) the peak wavelength. Joining these points over temperature traces the Planckian locus.

How to read it

The spectrum plot shows the peak moving to shorter wavelength as temperature rises.

The color patch shows the transition from red glow toward white.

The power curve highlights the fourth-power temperature dependence.

Learn Blackbody Color Temperature by dialogue

🙋
When reading Blackbody Color Temperature, where should I look first? Moving Blackbody temperature T changes both the plots and the result cards.
🎓
Start with Peak wavelength, but do not treat the number as the whole answer. Use Blackbody spectrum to confirm the assumed state, then read Color temperature patch for the distribution or trend. The spectrum plot shows the peak moving to shorter wavelength as temperature rises.
🙋
I can see why Blackbody temperature T changes Peak wavelength. How should I judge the influence of Emissivity ε?
🎓
Move Emissivity ε in small steps and watch Radiated power. That reveals which term is controlling the result. Ideal blackbody spectrum is determined by temperature alone. Real materials have wavelength-dependent emissivity, surface effects, transmission, and reflection. A single operating point is not enough; sweep the realistic scatter range.
🙋
What is Radiated power curve for? It feels like the ordinary curve already tells the story.
🎓
Radiated power curve is for finding boundaries where the condition becomes risky or margin collapses quickly. The color patch shows the transition from red glow toward white. In First-pass understanding of radiative heating and furnaces, the important question is often what happens after a small change, not only the nominal value.
🙋
So if Peak wavelength is within the target, can I accept the condition?
🎓
Treat this as a first-pass review. It helps with Comparing light-source color temperature and Teaching temperature dependence in thermal imaging or infrared radiation, but final decisions still need standards, measured data, detailed analysis, and vendor limits. The power curve highlights the fourth-power temperature dependence.

Practical use

First-pass understanding of radiative heating and furnaces.

Comparing light-source color temperature.

Teaching temperature dependence in thermal imaging or infrared radiation.

FAQ

Start with Peak wavelength and Radiated power. Then use Blackbody spectrum to confirm the assumed state and Color temperature patch to read distribution or bias. The spectrum plot shows the peak moving to shorter wavelength as temperature rises
Move Blackbody temperature T alone, then move Emissivity ε by a comparable amount and compare the change in Peak wavelength. Radiated power curve shows combinations where margin or performance changes quickly.
Use it for First-pass understanding of radiative heating and furnaces. Instead of trusting a single point, widen the input range and check whether Peak wavelength keeps enough margin before moving to detailed analysis.
Ideal blackbody spectrum is determined by temperature alone. Real materials have wavelength-dependent emissivity, surface effects, transmission, and reflection. Final decisions still require standards, measured data, detailed analysis, and vendor limits.

How to Use

  1. Enter absolute temperature in Kelvin (range 300–6000 K) using the tempVal slider or text field
  2. Set emissivity (0.0–1.0) to account for material absorptivity; polished steel ≈0.1, oxidized steel ≈0.8, blackbody =1.0
  3. Specify radiating surface area in m² to calculate total radiated power via Stefan–Boltzmann law
  4. Read peak wavelength from Wien's displacement law output and spectral radiance curve
  5. Observe visible-band intensity (400–700 nm) and infrared bias shift as temperature changes

Worked Example

A tungsten filament lamp operates at 2850 K with emissivity 0.35 and radiating area 0.0008 m². Peak wavelength = 2850 nm / 2850 = 1.01 μm (deep infrared). Radiated power = 0.35 × 5.670374×10⁻⁸ × (2850)⁴ × 0.0008 ≈ 1047 W. Visible-band index registers a low warm-glow value, infrared bias dominates (heat waste). Increasing to 3200 K shifts peak to 0.90 μm and power to ≈ 1665 W.

Practical Notes

  1. Ceramic kiln walls at 1400 K emit primarily mid-infrared (2.07 μm peak); low visible output explains dark appearance despite extreme heat
  2. Precision thermometry: pyrometers measure 8–14 μm band; match emissivity table (polished aluminum 0.04, anodized 0.9) to avoid 100+ K reading error
  3. LED color temp (6500 K "daylight") requires phosphor blend—pure blackbody spectrum cannot replicate; use visible-band index only as reference
  4. Industrial furnace design: higher emissivity coatings (0.85+) improve radiant efficiency but increase temperature uniformity challenges

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🎬 Watch it in motion

Why hot things glow red to white to blue — black-body radiation #Shorts
Why hot things glow red to white to blue — black-body radiation #Shorts