Hotter light shifts toward blue.
An ideal black body absorbs all incident radiation and emits a temperature-dependent continuous spectrum. As temperature rises, total emitted power increases and the spectral peak shifts to shorter wavelengths. The classical prediction failed at short wavelengths; quantised energy exchange helped resolve the discrepancy.
Wien’s law gives the wavelength of the peak for a wavelength-based spectrum. Photon energy is hf = hc/λ. A shorter-wavelength photon carries more energy, but brightness also depends on the number of photons arriving each second.
Hotter means a shorter peak
Explore the relationship
Wien’s law for an ideal black body. Multiply the horizontal temperature by the selected factor.
Tap or focus a plotted point to read its values.
View plotted data as a table
| Series | Temperature / K | Peak wavelength / nm |
|---|---|---|
| Peak wavelength / nm | 2000 | 1449 |
| Peak wavelength / nm | 2133.33 | 1358.44 |
| Peak wavelength / nm | 2266.67 | 1278.53 |
| Peak wavelength / nm | 2400 | 1207.5 |
| Peak wavelength / nm | 2533.33 | 1143.95 |
| Peak wavelength / nm | 2666.67 | 1086.75 |
| Peak wavelength / nm | 2800 | 1035 |
| Peak wavelength / nm | 2933.33 | 987.955 |
| Peak wavelength / nm | 3066.67 | 945 |
| Peak wavelength / nm | 3200 | 905.625 |
| Peak wavelength / nm | 3333.33 | 869.4 |
| Peak wavelength / nm | 3466.67 | 835.962 |
| Peak wavelength / nm | 3600 | 805 |
| Peak wavelength / nm | 3733.33 | 776.25 |
| Peak wavelength / nm | 3866.67 | 749.483 |
| Peak wavelength / nm | 4000 | 724.5 |
| Peak wavelength / nm | 4133.33 | 701.129 |
| Peak wavelength / nm | 4266.67 | 679.219 |
| Peak wavelength / nm | 4400 | 658.636 |
| Peak wavelength / nm | 4533.33 | 639.265 |
| Peak wavelength / nm | 4666.67 | 621 |
| Peak wavelength / nm | 4800 | 603.75 |
| Peak wavelength / nm | 4933.33 | 587.432 |
| Peak wavelength / nm | 5066.67 | 571.974 |
| Peak wavelength / nm | 5200 | 557.308 |
| Peak wavelength / nm | 5333.33 | 543.375 |
| Peak wavelength / nm | 5466.67 | 530.122 |
| Peak wavelength / nm | 5600 | 517.5 |
| Peak wavelength / nm | 5733.33 | 505.465 |
| Peak wavelength / nm | 5866.67 | 493.977 |
| Peak wavelength / nm | 6000 | 483 |
| Peak wavelength / nm | 6133.33 | 472.5 |
| Peak wavelength / nm | 6266.67 | 462.447 |
| Peak wavelength / nm | 6400 | 452.813 |
| Peak wavelength / nm | 6533.33 | 443.571 |
| Peak wavelength / nm | 6666.67 | 434.7 |
| Peak wavelength / nm | 6800 | 426.176 |
| Peak wavelength / nm | 6933.33 | 417.981 |
| Peak wavelength / nm | 7066.67 | 410.094 |
| Peak wavelength / nm | 7200 | 402.5 |
| Peak wavelength / nm | 7333.33 | 395.182 |
| Peak wavelength / nm | 7466.67 | 388.125 |
| Peak wavelength / nm | 7600 | 381.316 |
| Peak wavelength / nm | 7733.33 | 374.741 |
| Peak wavelength / nm | 7866.67 | 368.39 |
| Peak wavelength / nm | 8000 | 362.25 |
| Peak wavelength / nm | 8133.33 | 356.311 |
| Peak wavelength / nm | 8266.67 | 350.565 |
| Peak wavelength / nm | 8400 | 345 |
| Peak wavelength / nm | 8533.33 | 339.609 |
| Peak wavelength / nm | 8666.67 | 334.385 |
| Peak wavelength / nm | 8800 | 329.318 |
| Peak wavelength / nm | 8933.33 | 324.403 |
| Peak wavelength / nm | 9066.67 | 319.632 |
| Peak wavelength / nm | 9200 | 315 |
| Peak wavelength / nm | 9333.33 | 310.5 |
| Peak wavelength / nm | 9466.67 | 306.127 |
| Peak wavelength / nm | 9600 | 301.875 |
| Peak wavelength / nm | 9733.33 | 297.74 |
| Peak wavelength / nm | 9866.67 | 293.716 |
| Peak wavelength / nm | 10000 | 289.8 |
Explore: Double absolute temperature and compare the peak wavelength.
A black body at 5800 K has b = 2.898 × m K.
- λmax = b/T ≈ 5.00 × m.
- The peak is approximately 500 nm.
Assumed knowledge
SI prefixes and scientific notation.
Learning checkpoints & source
YOUR LEARNING CHECKPOINT- Interpret black-body radiation.
- Use Wien’s law and photon energy.